presence of starch experiment

Experiment to Test the Presence of Starch in the Given Food Sample

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Experiment to Test the Presence of Starch in the Given Food Sample !

Experiment 3.1:

Objective :.

To test the presence of starch in the given food sample.

Apparatus and materials required :

Test tubes, test-tube stand, test-tube holder, spirit lamp, dropper, filter paper, iodine solution, distilled water, and foodstuff (potato, rice, wheat or maize grains).

Starch, a complex carbohydrate, is composed of 15%-20% amylose and 80%-85% amylopectin. It is found in different kinds of cereals such as rice, wheat, maize, etc. After reacting with iodine solution starch forms a dark, blue-black compound. The appearance of blue-black colour is due to the presence of amylase in starch.

Procedure :

1. Take a few small, freshly cut pieces of potato or a few grains of rice or wheat or maize in a clean test tube.

2. Pour 10 mL distilled water into the test tube.

3. Now, boil the contents of the test tube for about 5 minutes.

4. Allow the test tube to cool.

5. Filter the contents of the test tube through a filter paper.

6. Test the obtained filtrate for the presence of starch by the following method.

Precautions :

1. Use test-tube holder for holding the test tubes and keep the mouth of the test tube away from yourself while heating.

2. Use clean test tubes.

3. Do not use too much of iodine solution.

Experiment 3. 2:

To test the presence of the adulterant metanil yellow in dal (pulse)

Test tubes, test-tube stand, test-tube holder, conc. HCl, mortar-pestle, filter paper, distilled water and a sample of dal

Metanil is a cheap dye which is commonly used in colouring non-food items like clothes. Government of India has introduced “Prevention of Food Adulteration Act” to prevent the use of harmful chemicals such as this dye in foodstuffs.

1. Grind 3-5 g of dal in a mortar-pestle.

2. Take this powdered dal in a clean test tube.

3. Pour 10 mL distilled water into the test tube and shake it well.

4. Filter the contents of the test tube through a filter paper and use the filtrate to test for metanil yellow by the following method.

Observation:

1. Always use clean test tubes.

2. Use test-tube holder at the time of adding conc. HCI and keep the mouth of the test tube away from yourself.

3. Do not add excess conc. HCI.

4. Handle the bottle of conc. HCI carefully.

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Iodine Test: Description, Principle, Procedure And Result Interpretation

What is iodine test.

The iodine test was first described by J.J Colin and H.F Gaultier de Claubry and independently by F. Stromeyer in 1884. The iodine test is used to test for the presence of starch in a given analyte. The test can be qualitative or quantitative.

Objective Of Iodine Test

• To test for the presence of starch in biological molecules.

Principle Of Iodine Test

This test depends upon the property of adsorption possessed by the large polysaccharide molecules. Starch contains alpha-amylose, helical saccharide polymer and amylopectin. Triiodide anion instantly produces an intense blue-black color upon contact with starch. This reaction is as a result of the formation of polyiodide chains from the reaction of starch and iodine. The amylose or straight chain portion of starch, forms helices where iodine molecules assemble, forming a dark-blue/black color. The amylopectic or branched portion of starch forms much shorter helices and iodine molecules are unable to assemble, leading the color to be of an orange/yellow hue.

Generally amylopectin, glycogen and cellulose do not form alpha-helices, they do not complex well with iodine, therefore, they do not show the blue-black color; instead they show a purple or brown color. Monosaccharides on the other hand do not interact with the iodine, therefore no color is produced.

The color obtained depends upon the length of the unbranched or linear chain available for complex formation. Also, the intensity of the color produced decreases with increasing temperature and with the presence of water-miscible organic solvents such as ethanol. Iodine test cannot be performed at very low PH due to the hydrolysis of the starch under these conditions.

Reagent And Material Required

• Iodine Reagent: 0.5 ml iodine diluted in 5 ml distilled water and mixed with 10% potassium iodide to form Iodine solution (Lugol’s iodine)
• Dropper or pipette
• Test sample or solution

Iodine Test Procedure

• Take 1 ml of the test sample in a clean, dry test tube.
• Similarly, take another 1 ml of distilled water in another tube.
• Add about 2-3 drops of Iodine solution to both test tubes and mix thoroughly.
• Observe the appearance of color in the test tubes.
• Heat the test tubes in the water bath until the color disappears.
• Take the test tubes out for cooling.
• Note down the appearance of color seen in the test tubes.

Iodine Test Result Interpretation

• Positive Test : A positive test is indicated by presence of a blue-black or purple color in the test tube. This confirms presence of starch.
• Negative Test: A negative test is indicated by no change in color of iodine solution. This confirms absence of starch.

Limitations Of Iodine Test

• This test cannot be done under acidic conditions as the starch hydrolyses under such circumstances.
• This test is a qualitative test and doesn’t signify the concentration of starch.

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Microbe Notes

Leaf Starch Test: Principle, Procedure, Results, Uses

Starch in a leaf can be easily detected in a lab with the help of iodine solution. This test is called the ‘Leaf Starch Test’ or ‘Iodine Test for Starch’.

Green leaves are the food factory of plants. Green leaves have abundant chloroplasts – special organelles where the photosynthesis process takes place – so, a large portion of photosynthesis occurs in the leaves of a plant. The glucose produced during photosynthesis is stored as an energy reserve in the form of starch in the leaf, stem, branches, roots, and fruits of a plant. Starch is one of the abundant natural carbohydrates consumed in the diet by humans and other animals as an energy source.

Starch is a complex polymeric carbohydrate (polysaccharide) stored as a reserve food material in plants. It is formed of glucose monomers joined together by a glycosidic bond. The glucose units exist in two forms in natural starch; amylose and amylopectin . Amylose is water insoluble straight-chain polymer of D-glucose subunits linked together by α-1,4 glycosidic bond. Amylopectin is a water-soluble branched chain polymer of D-glucose subunits linked together by α-1,6 glycosidic bond.

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Objectives of Leaf Starch Test

• To detect the presence of starch in a leaf
• To assess the extent of photosynthesis occurring in the leaf

Principle of Leaf Starch Test

Iodine is insoluble in water; but when potassium iodide is added, it dissociates into K + and I -, and the resulting I – reacts with molecular iodine (I 2 ) to form a triiodide complex (I 3 – ). The triiodide complex can further associate with molecular iodine and form pentaiodide complex (I 5 – ) and so on.

The amylose component of starch is arranged in the form of helical coils. When the iodine-iodide solution is added over starch molecules, the negatively charged polyiodide (mainly triiodide, I 3 – ) slips inside the helices of the amylose chain forming a charge transfer complex. Electrons in this charge transfer complex absorb light energy and get excited. This phenomenon is perceived by the human eye as intense blue-black color.

Hence, in the presence of starch, a blue-black colored complex is formed when the iodine-iodide solution is added over the starch. The intensity of the blue-black color is proportional to the quantity of amylose (or starch) but doesn’t give an exact quantitative (concentration) value. Hence, the test is a qualitative type test.

Requirements for Leaf Starch Test

Procedure of Leaf Starch Test

• Pluck a green leaf of any outdoor plant. A medium size leaf, preferably, a leaf recently exposed to sunlight is better for this test. 
• Boil about 250 mL water in a beaker and put the leaf in the beaker and let it boil for a few minutes (2 to 5 minutes) till its waxy coat got off and it gets soft.
• Using forceps, take out the leaf and spread it on a petri plate. 
• Place the leaf in a test tube and pour ethanol (90% or more v/v) till the leaf submerses. 
• Place the test tube in the beaker with boiling water (or in a water bath) and let the ethanol boil till the leaf decolorizes. Take out the leaf after 5 to 10 minutes if it doesn’t decolorize completely. 
• Place the leaf on a petri plate and spread it properly and rinse with cold water. 
• Using a dropper, add a few drops of iodine solution over the leaf to cover it. 
• Examine the color of the leaf after 2 minutes of the addition of iodine solution.

Observation of Leaf Starch Test

• The leaf will decolorize and become whitish after boiling in an ethanol solution. 
• The leaf will turn dark blue-black color after the addition of iodine solution. 

Result and Interpretation of Leaf Starch Test

The development of a blue-black color over the surface of the leaf indicates the presence of starch in the leaf. It suggests that the leaf was undergoing a photosynthesis process and had starch within it. 

Precautions

• Use forceps to place a leaf in and out of the boiling water and ethanol solution. 
• Always use green leaves exposed to sunlight for better results. 
• Do not direct the mouth of the test tube with ethanol towards your face while boiling it. 

Uses of Leaf Starch Test

• In the assessment of the photosynthetic activity in leaves.
• It is used to study photosynthesis patterns, starch accumulation, and depletion patterns in leaves, and assessment of environmental factors influencing photosynthesis and starch accumulation. 
• It is used as a teaching tool for basic-level students to introduce them photosynthesis process in leaves and carbohydrate storage. 

Limitations of Leaf Starch Test

• It is a qualitative test and hence only indicates the presence or absence of starch but doesn’t represent the quantity of starch present. 
• This test can be easily influenced by exposure of the leaf to sunlight, condition of the leaf, and quality and quantity of iodine solution. 
• https://www.bbc.co.uk/bitesize/guides/zpcvbk7/revision/3
• https://practicalbiology.org/standard-techniques/testing-leaves-for-starch-the-technique
• https://www.wikihow.com/Test-for-Starch
• https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Supplemental_Modules_(Biological_Chemistry)/Carbohydrates/Case_Studies/Starch_and_Iodine
• https://www.biologyonline.com/dictionary/iodine-test
• https://microbiologynote.com/iodine-test/
• https://learning-center.homesciencetools.com/article/test-for-starch-photosynthesis/
• https://science.cleapss.org.uk/resource-info/pp088-testing-leaves-for-starch.aspx

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Science Projects > Life Science Projects > Test for Starch in Plants  

Test for Starch in Plants

Photosynthesis is the process in which green plants (primarily) convert energy from the sun’s light into usable, chemical energy. Plants require energy for growth, reproduction, and defense. Excess energy, created from photosynthesis, is stored in plant tissue as starch. Starch is a white and powdery substance. It houses glucose, which plants use for food. The presence of starch in a leaf is reliable evidence of photosynthesis. That’s because starch formation requires photosynthesis.

( Adult supervision required. )

Starch Testing Experiment

What you need:.

• Beaker or glass jar
• Saucepan on the stove
• Ethyl alcohol
• Iodine solution

Test for starch in plants:

1. Place one of the plants in a dark room for 24 hours; place the other one on a sunny windowsill.

2. Wait 24 hours.

3. Fill the beaker or jar with ethyl alcohol.

4. Place the beaker or jar in a saucepan full of water.

5. Heat the pan until the ethyl alcohol begins to boil.

6. Remove from the heat.

7. Dip each of the leaves in the hot water for 60 seconds, using tweezers.

8. Drop the leaves in the beaker or jar of ethyl alcohol for two minutes (or until they turn almost white).

9. Set them each in a shallow dish.

10. Cover the leaves with some iodine solution and watch.

What Happened:

The hot water kills the leaf and the alcohol breaks down the chlorophyll, taking the green color out of the leaf. When you put iodine on the leaves, one of them will turn blue-black and the other will be a reddish-brown. Iodine is an indicator that turns blue-black in the presence of starch. The leaf that was in the light turns blue-black, which demonstrates that the leaf has been performing photosynthesis and producing starch.

Try the test again with a variegated leaf (one with both green and white) that has been in the sunlight. A leaf needs chlorophyll to perform photosynthesis — based on that information, where on the variegated leaf do you think you would find starch?

Buy Testing For Starch Experiment Kit

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How to Test for Starch

Last Updated: August 11, 2023 Fact Checked

This article was co-authored by Bess Ruff, MA . Bess Ruff is a Geography PhD student at Florida State University. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group. There are 8 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 114,946 times.

Starch tests are used to detect the presence of starch in leaves, foods, and liquids. The process is easy and can quickly tell you if a leaf has undergone photosynthesis by its starch levels or if a food or liquid contains starch. Using iodine to test for starch is a simple way to engage your students in a classroom experiment or create an educational afternoon at home.

Testing Leaves for Starch

• Although you can use any green leaf for this experiment, hibiscus leaves tend to produce better results. [2] X Research source

• A Bunsen burner is a type of gas burner that heats liquids and solids in chemical experiments.
• Your leaf will be done boiling when it has become completely soft. [5] X Research source
• Boiling your leaf will remove the waxy covering or cuticle that may prevent the entry of the iodine. [6] X Research source
• It is not necessary to turn off hot plates or electric water baths at this time. [8] X Research source

• A boiling tube is a cylinder tube of thin glass. It will be open on one end and will be able to withstand extreme temperatures. A test tube is suitable for this experiment.
• It is better to use a hot plate or water bath for this step as ethanol is extremely flammable.
• You may need to replenish your ethanol levels if the ethanol is no longer covering your leaf completely. [11] X Research source
• Your leaf is done boiling when all of the green coloring is transferred to the ethanol, leaving your leaf colorless. [12] X Research source
• Boiling your leaf in ethanol will cause it to become brittle. By adding a small amount of cold water, it will help the leaf regain a soft texture.
• You can also place your leaf in a petri dish, rather than placing it directly on the white tile. [15] X Research source
• Soaking your leaf is not necessary, but it will increase the accuracy of your results. [17] X Research source

Searching for Starch in Foods

• Lighter colored foods will work best for this experiment. [20] X Research source
• Control samples are not required but can be very useful when analyzing your results.
• You can add the iodine directly to your samples or place the iodine in the bottom of a cup, lay your sample on a paper towel, and place it on top of the iodine. [24] X Research source
• If you are unable to find an iodine solution you can also use Betadine (povidone-iodine mix), Lugol’s (a mixture of iodine and potassium), or a tincture (where the iodine is dissolved in water or alcohol). [25] X Research source

Conducting a Liquid Starch Test

• If you opted to place your liquid on a tile, add the drop of iodine directly to the liquid.

Expert Q&A

• Never allow your children to conduct this experiment unsupervised. Thanks Helpful 0 Not Helpful 1
• Always keep ethanol away from open flames, unless it is held in a test tube. [31] X Research source Thanks Helpful 0 Not Helpful 1
• Wash your hands immediately after using iodine as it can stain skin and clothing. Stains on the skin are temporary. Thanks Helpful 1 Not Helpful 0
• Always wear eye protection while handling chemicals and around boiling liquids. [32] X Research source Thanks Helpful 0 Not Helpful 1
• Always use heat-resistant gloves when dealing with open flames and hot plates. Thanks Helpful 0 Not Helpful 1

Things You'll Need

• Bunsen burner or hot plate
• 250 mL (8.5  fl oz) beaker
• Boiling tube
• Test tube rack
• A leaf to be tested
• 90% ethanol
• Iodine Solution
• Eye protection goggles
• Heat resistant gloves
• Dropping pipette
• A starchy food such as a raw potato, pasta, or bread
• A non-starchy food such as apples, cucumbers, or pure sugar.
• Small, disposable, plastic cups
• Newspaper to cover your work area
• A light-colored liquid
• Glass Rod to stir
• Eye protection

You Might Also Like

• ↑ https://practicalbiology.org/standard-techniques/testing-leaves-for-starch-the-technique
• ↑ https://www.youtube.com/watch?v=E9CSyXS3pXc
• ↑ http://www.preproom.org/practicals/pr.aspx?prID=1037
• ↑ http://brilliantbiologystudent.weebly.com/testing-a-leaf-for-the-presence-of-starch.html
• ↑ http://www.nuffieldfoundation.org/practical-biology/testing-leaves-starch-technique
• ↑ http://kitchenpantryscientist.com/starch-test/
• ↑ http://www.webexhibits.org/causesofcolor/6AC.html
• ↑ http://brilliantbiologystudent.weebly.com/iodine-test-for-starch.html

About This Article

Medical Disclaimer

The content of this article is not intended to be a substitute for professional medical advice, examination, diagnosis, or treatment. You should always contact your doctor or other qualified healthcare professional before starting, changing, or stopping any kind of health treatment.

Read More...

To test foods for starch, start by cutting your food into small slices and placing them in disposable plastic cups to keep your samples clean. Once your test foods are ready, add 1 drop of water to the cup that contains your control sample. After you control sample is ready, add 1 to 2 drops of iodine to the sample being tested, putting the iodine directly onto your sample or placing it in the bottom of the cup. Notice if your iodine has turned blue-black in color, which indicates that starch is present. If, on the other hand, your sample looks brown, there’s no starch present. For more tips from our Science co-author, including how to test for starch in liquids, keep reading! Did this summary help you? Yes No

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Iodine test for Starch- Its Principle, Reagents, Procedure etc

October 2, 2016 by Admin Leave a Comment

What is Starch Iodine test?

The Iodine Test for Starch is utilized to decide the presence of starch in natural materials. The test can be subjective or quantitative. The iodine test is utilized to test for the presence of starch. At the point when treated with IKI solution, iodine broke up in a watery arrangement of potassium iodide the tri-iodide-anion edifices with starch, creating a serious blue/purple coloring. The coloring can be differentiated outwardly with centralizations of iodine as low as 2×10-5 M at 20 °C. Be that as it may, the force of the colors reduces with expanding temperature and with the presence of water-miscible natural solvents, for example, ethanol. The test can’t be performed at low pH because of the hydrolysis of the starch under these conditions.

Starch Indicator:

Starch is frequently utilized as a part of science as a pointer for redox titrations where tri-iodide is available. Starch shapes an extremely dull blue-dark complex with tri-iodide which can be made by blending iodine with iodide (regularly from potassium iodide). The shade of the starch complex is deep to the point, that it can be recognized outwardly when the grouping of the iodine is as low as 0.00002 M at 20 °C. The shading affectability reduces with expanding temperature (ten times less delicate at 50 °C), and upon the expansion of natural solvents, for example, ethanol. Between iodine titrations, concentrated iodine arrangements must be reacted with some titrant, frequently thiosulfate, to uproot the greater part of the iodine before the starch is included. This is because of the insolubility of the starch-iodine complex which might keep a percentage of the iodine reacting with the titrant. Near the end-point, the starch is included, and the titration procedure is continued considering the measure of thiosulfate included before including the starch.

Principle of Iodine test for Starch:

You will be trying for the presence of this unpredictable starch or in leaves as a major aspect of a photosynthesis experiment being a Biology student. These are subjective tests. If you think about science too, you ought to focus guideline of the test, as it clarifies how starch goes about as a marker for Redox Titrations or in the ‘Iodine Clock Reaction’. These expansions of the Starch Iodine test yield subjective results. The sole reagent required for the test is basic iodine arrangement (0.1 M potassium tri-iodide arrangement).

Procedure of Starch Iodine test:

Note: Before going down to perform the procedure for this test, you need to know that it depends on certain conditions. These conditions are whether sample used in the test is solid or a liquid. Now to make it easier for you, I am going to perform the tests in two different headings presenting for both solid and liquid. Now whether your sample is liquid or a solid, you can go for either of the test procedures.

If the sample is Solid:

• Take two fruits or vegetables because to start you will need to peel off their skin. You can take different fruits or in vegetables, Potato could be a great agent. Once you have chosen your thing, peel off their skin and get ready for the test.
• Next thing you will need to do is to remove the powdered food samples. You must do this by using a neat and clean spatula otherwise your test could be a disaster.
• Now take basic iodine solution potassium and add 2 to 3 drops of it on the food sample. Doing this on a white tile will help the purpose better because visuals are better on a white tile.
• Once being done with that, observe the results carefully and you are done.

If the sample is Liquid:

Now in the case of liquid, the test goes whole different. It still remains simple so just follow the procedure below to get positive results for the presence of starch in the case of liquid.

• Take a test tube. In the test tube, you will have to put 10 cm3 of the liquid sample of the test. Make sure that you do it carefully and nothing spills out.
• Now again in the test tube, you will have to pour down exact five drops of iodine solution and make sure that you don’t the exceed the number 5.
• Once being done with the above two steps, note down if there are any color changes appearing because this concerns the results.

Precautions before performing:

Before you perform the Iodine test for starch, here is a list of precautions that you need to take care of before and while performing.

• Make sure that amount you’re taking of samples and liquid drops are the same as mentioned in the procedure.
• Also, make sure that the test tube you are using must be cleaned and washed very neatly. There must not remain any impurity other than the natural stuff in the test tube.
• Observe colors at the end of the tests very carefully and note down results on a notepad to avoid future inconvenience.

Once taken these precautions, I am sure that your test should be 100% positive.

Results of Starch Iodine Test:

When the starch is present:.

In the case of presence of starch, the color of the solution changes. The color change should be a blue-black color which appears only in the case if positive results which are that the starch is present in the solution.

When the starch is not present:

After performing the whole experiment when you are observing and no color change appears in the solution then it means that starch is not present in the solution. The result could also be negative if the experiment was not performed properly but if performed carefully and the color change doesn’t appear then it means starch is not present in the solution.

Final Words:

So this was all from a very easy test to check the vicinity of starch with the help of Iodine test. Was this article helpful in your science study? Please us your feedback and also mention if I missed something. Keep visiting our site for more amazing medical sciences tests.

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Why Does Iodine Turn Starch Blue?

Author: Catharina Goedecke

Iodine Test

Using iodine to test for the presence of starch is a common experiment. A solution of iodine (I 2 ) and potassium iodide (KI) in water has a light orange-brown color. If it is added to a sample that contains starch, such as the bread pictured above, the color changes to a deep blue. But how does this color change work?

Starch is a carbohydrate found in plants. It consists of two different types of polysaccharides that are made up of glucose units which are connected in two different ways. One is the linear amylose and the other is the branched amylopectin (pictured below).

Amylose is the compound that is responsible for the blue color. Its chain forms a helix shape, and iodine can be bound inside this helix (pictured below).

Charge-Transfer Complexes

The colors are caused by so-called charge transfer (CT) complexes. Molecular iodine (I 2 ) is not easily soluble in water, which is why potassium iodide is added. Together, they form polyiodide ions of the type I n – , for example,  I 3 – , I 5 – , or I 7 – . The negatively charged iodide in these compounds acts as charge donor, the neutral iodine as a charge acceptor. Electrons in such charge-transfer complexes are easy to excite to a higher energy level by light. The light is absorbed in the process and its complementary color is observed by the human eye.

In the case of the aqueous solution of polyiodides, the absorptions of the different species lead to an overall brownish color. Once amylose is added, it forms another CT complex, Here, the amylose acts as a charge donor and the polyiodide as an acceptor. This complex absorbs light of a different wavelength than polyiodide, and the color turns dark blue.

Polyiodide Chains

The exact structure of the polyiodides inside the amyloid helix is not clear. The amylose-iodine complex is amorphous (i.e., it does not form ordered crystals), which has made it difficult to determine its structure. It has been proposed that the species inside the helix are repeated  I 3 – or I 5 – units.

However, Ram Seshadri, Fred Wudl, and colleagues, University of California, Santa Barbara, USA, have found evidence that infinite polyiodide chains I n x– are contained in the amylose-iodine complex [1]. The team investigated a related system, a pyrroloperylene–iodine complex, to study its properties as an organic electronic conductor. The material is crystalline, and therefore, the team was able to determine its structure using X-ray crystallography. They found nearly linear polyiodide chains in-between stacks of pyrroloperylene. It turned out that the material containing these chains absorbs light at very similar wavelengths to the amylose-iodine complex, which supports the hypothesis that similar polymeric chains form in the iodine test for starch.

[1] Sheri Madhu, Hayden A. Evans, Vicky V. T. Doan-Nguyen, John G. Labram, Guang Wu, Michael L. Chabinyc, Ram Seshadri, Fred Wudl, Infinite Polyiodide Chains in the Pyrroloperylene-Iodine Complex: Insights into the Starch-Iodine and Perylene-Iodine Complexes , Angew. Chem. Int. Ed. 2016 , 55 , 8032–8035. DOI: 10.1002/anie.201601585

• Der Iod-Stärke-Komplex (in German), www.chemieunterricht.de 2006 . (accessed November 24, 2016)
• The structure of the blue starch-iodine complex , Wolfram Saenger, Naturwissenschaften 1984 , 71 , 31–36. DOI: 10.1007/bf00365977

this article is quite helpful .. thank you ✨

Thank you guys

where the h*** is the volume and page number to cite this

Dear Reader, We do not have volumes or page numbers. You can cite the article as: C. Goedecke, Why Does Iodine Turn Starch Blue?, ChemistryViews 2016 . https://doi.org/10.1002/chemv.201600103 Best regards, Your ChemistryViews Team

Interesting light absorbing properties

Nice informative post

Very informative thank you very much

Who is the publisher?

Dear Reader, You can cite the article as: C. Goedecke, Why Does Iodine Turn Starch Blue?, ChemistryViews 2016. https://doi.org/10.1002/chemv.201600103 Best regards, Your ChemistryViews Team

Very interesting and helpful

Very helpful imformation, thank you

Wow that’s awesome

this is awesome

really cool but no words

would iodiDE alone form the same reaction? or is iodiNE specifically needed to react with the glycogen

Thanks for this.. very helpful

What does it mean, when the water become crystal clear after you added iodine into the water?

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• Biology Article
• Test For The Presence Of Sugar Starch Proteins And Fats Detection In Suitable Plant And Animal Materials

Test For The Presence Of Sugar, Starch, Proteins, And Fats - Detection In Suitable Plant And Animal Materials

Table of Contents

Test for Sucrose

Test for starch, test for proteins, test for fats.

To detect the presence of sugar(sucrose), starch, proteins, and fats in suitable animal and plant materials.

Nutrition is a source through which living entities obtain food for the body to get fueled with energy. Therefore the food we eat must be well-balanced with all the substances that are required by our body to perform daily activities, these substances are known as nutrients.

Nutrients nourish the body by releasing the energy required for the body’s growth. Some of the nutrients found in food are:

• Carbohydrates
• Dietary fibres

What are proteins?

They are body-building nutrients which aid in the repair of damaged body parts and also in the growth of the body.

What are vitamins and minerals?

These nutrients are reflected to be protective food. They protect us from diseases by providing resistance against germs that are known to cause diseases.

What are carbohydrates?

Carbohydrates are nutrients that provide energy to the body instantly. Fats are also energy-giving foods and store energy.

Carbohydrates contain starch, sugars, and fibres which consist of sugar molecules containing hydrogen, carbon, and oxygen. Carbohydrates can be categorized into:

• Simple carbohydrates – They are composed of 1 or 2 units of sugar, hence can be broken down and absorbed easily. Simple carbohydrates are further divided into:
• Monosaccharides – Composed of one sugar unit
• Disaccharides – Consists of 2 chemically-associated monosaccharide units. Example – Lactose, Maltose, Sucrose, etc.
• Oligosaccharides – Composed of less than 10 monosaccharides parts
• Polysaccharides – composed of a large number of polysaccharides. Example – Glycogen, starch, and cellulose

The presence of sucrose can be tested in a sample using Benedict’s test.

Material Required

• Benedict’s Reagent
• Sugar cane extract
• Concentrated HCl
• NaOH solution
• Test tube holder
• Take a clean and dried test tube and add sugar cane extract into it.
• Now carefully add a few drops of concentrated HCl using a dropper to the test tube.
• Hold the test tube securely with the help of a test tube holder.
• Place the test tube near the Bunsen burner and allow the solution to boil for two minutes.
• While boiling, the hydrolysis of sucrose occurs and the fructose converts to glucose.
• With the help of a dropper, add a few drops of NaOH solution to the test tube so that the solution turns alkaline.
• Now add a few drops of Benedict’s reagent with the help of a dropper into the test tube.
• With the help of a test tube holder, place the test tube near the Bunsen burner and allow the solution to boil for a few minutes.
• Observe the changes.

Observation

The colour of the solution colour from blue colour to green colour. From green colour, it finally changes to brick red or orange colour. This indicates that the solution contains glucose.

• Potato extract
• Iodine solution
• Take a clean and dried test tube and add potato extract into it.
• Add five to six drops of iodine solution with the help of a dropper into the test tube.
• Keep the test tube undisturbed and allow the mixtures to stand for a few seconds.

The presence of starch in the potato extract is indicated when the colour changes to a blue-black colour.

The presence of proteins in a sample can be detected by the following tests:

• Biuret Test
• Xanthoproteic Test
• Million’s Test

1. Biuret Test

• 40% NaOH solution
• Egg Albumin
• Take a clean and dried test tube and add egg albumin into it.
• Now add a few drops of 40% NaOH solution with the help of a dropper into the test tube containing the egg albumin.
• With the help of a dropper, add 2 to 3 drops of 1% CuSO4 solution into the same test tube contained in the egg albumin.
• Now shake the test tube slowly in order to mix the solution present in it completely.
• Keep the test tube undisturbed and allow the mixtures to stand for 5 minutes. After a few minutes, observe the changes.

The solution in the test tube appears to be violet in colour. This indicates that the sample that is tested contains proteins.

2. Xanthoproteic Test

• Ammonia solution
• Concentrated HNO3
• Egg albumin
• Add five drops of concentrated HNO3 with the help of a dropper into the test tube containing the egg albumin.
• Holding the test tube securely with a test tube holder, bring the sample to a boil over a burner.
• As the solution starts to boil, a yellow precipitate is formed.
• Now add a few drops of ammonia solution into the test tube slowly.
• Stir the test tube continuously in order to mix the solution completely. After a few minutes, observe the changes.

The sample contained in the test tube, which appeared to have yellow precipitate changed its colour to orange. This indicates that the sample contains proteins.

3. Million’s Test

Materials Required

• Million’s Reagent
• With the help of a dropper, add a few drops of Million’s reagent into the test tube containing the egg albumin.
• Keep the test tube undisturbed and allow the mixtures to stand for 5 minutes.
• After a few minutes, observe the changes.

The sample indicates the presence of proteins when the colour changes to pink.

The presence of fats in a sample can be detected by the following tests:

• Sudan III Test
• Paper Spot Test

1. Sudan III Test

• Sudan III Solution
• Take a clean and dried test tube and add a few drops of oil into it.
• Now into the same test tube, add five to six drops of the Sudan III reagent with the help of a dropper.
• Stir the test tube continuously and allow the solution to stand for a while.
• After a few seconds, observe the changes.

The presence of fat in the sample is indicated when pink colour droplets appear on the test tube.

2. Paper Spot Test

• A piece of white paper
• Peanut seeds
• Watch glass
• On the piece of white paper, place the fresh peanut seeds.
• Crush and rub the peanut seeds on the white paper.
• Remove the peanut seed remaining on the watch glass.
• Observe the changes on the piece of white paper.

The spot where the peanut seeds are rubbed turns translucent. This indicates the presence of fats in the sample.

Viva Questions

Q.1. List examples of simple carbohydrates.

A.1. Simple carbohydrates are present in the form of fructose in fruits, in the form of lactose in milk and in the form of sucrose in table sugar.

Q.2. What are stachyose and raffinose?

A.2. They are examples of oligosaccharides and are categorized under complex carbohydrates.

Q.3. What are peptide linkages?

A.3. Proteins are made up of a large number of amino acids that are linked together by specific linkages known as peptide linkages. The amino acids comprise both carboxylic acids and an amino group.

Q.4. What is the xanthoproteic test?

A.4. It is used to detect the presence of proteins that contain aromatic amino acid units.

The benzene ring present in the amino acid , upon heating, is nitrated to form a yellow nitro compound. It switches to orange colour with the presence of an alkali.

Q.5. What do fats contain?

A.5. They are complex molecules. Fats contain glycerol and fatty acids.

Q.6. What is a Fehling’s Test used for?

A.6. It is used to detect the presence of aldehydes and reducing sugars. Fehling’s solution is a deep blue-coloured solution. This test is performed with glucose, fructose, sucrose, and maltose.

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• Why We’re Unique

Test fruits or fruit juices for starch

Introduction: (initial observation).

While learning about plant growth and photosynthesis, we learned that green plants use the energy from the sunlight, water from the ground and carbon dioxide gas from the air to make starch. Starch is the reservoir of food for plants. In this project you will test the presence of starch in edible plant parts, specially fruits. For better results, you must make your own juice. Processed juice sold in stores may have gone through stages to lose their starch content.

Try green fruits as well as ripe fruits. Also try corn, potato, carrot, broccoli, cantaloupe, cucumber, eggplant. Do not restrict yourself to the sweet fruit juices that you usually drink. Most such juice have no starch at all.

By selecting variations of green and ripe plants, you can also determine if the amount of starch changes as the fruit ripen.

Dear This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “ Ask Question ” button on the top of this page to send me a message.

If you are new in doing science project, click on “ How to Start ” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about starch and how it can be tested. Read books, magazines or ask professionals who might know in order to learn about the sources of starch. Keep track of where you got your information from.

Find out about starch and how it is made. Read books, magazines or ask professionals who might know in order to learn about the factors affecting the production of starch. Keep track of where you got your information from.

How to make 1% Cornstarch solution?

• Measure 10 grams of starch and dissolve it in about 100ml of water. Mix it to get a milky solution.
• In a glass beaker or cooking pot that is graduated or marked for one liter, heat up about 600 ml water to boil.
• Slowly add the milky solution that you have made to the hot water and continue stirring until the solution is clear (as much as possible).
• Add water to the solution to bring it up to one liter. That will make a 1% solution of starch.

Estimate all the measurements if you don’t have scales or measuring cups. A 1% solution of starch is a solution that contains one part starch and 99 parts of water (by weight). Starch does not dissolve in hot water. That is why you initially mix it with cold water.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement. Starch in food is hazardous for people with disease such as diabetes. In order to avoid starch, patients need to know which foods or fruits contain starch. In this project you will identify some of the fruits, vegetables and foods that contain large amounts of starch.

Some of the questions related to starch are:

• What foods contain starch?
• What vegetables contain starch?
• What industrial products contains starch (Paper, Envelop, Stamp, Glue, Fabric)
• How do starch molecules break down to sugar molecules?
• What papers contain starch?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

The type of food that we test is a manipulated or independent variable for our investigation. (In other words we choose different variations of food to test). The dependent variable is Starch presence (Yes, No).

I n other words presence of starch in food depends on the type of food.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Following are some samples of Hypothesis for some sample Questions.

Q: What foods contain starch?

H: Among the carrot, broccoli and corn, the corn contains starch but broccoli and carrot don’t. My hypothesis is based on my observation of products in grocery stores. I have seen packs of corn starch but I have not seen packs of broccoli starch or carrot starch.

Q: What papers contain starch?

H: Among copy paper, currency paper, and newspaper paper, copy paper contains starch. My hypothesis is based on my observation of the color of starch that is white, so gray or brown papers are most likely starch free papers.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Testing Fruit juices for presence of starch

Introduction:

Starch is a substance produced by green plants during the process of photosynthesis. In our body, starch will be converted to sugar which is a high energy food.

Starch can be identified using iodine solution. A solution of iodine added to starch will form a dark blue compound. This method is used to identify starch.

All plants have some type of fruit. Certain fruits are edible and are used as food. Depending on the type of fruit, we may be able to eat it raw or not. For example Cucumber is fruit that we eat it raw while egg plant is a fruit that we eat after cooking.

In this experiment we will test all fruits in raw form. Cooking may modify the composition of fruit material or change the amount of starch.

To test a fruit, cut it in peaces, filter the extract and test the clear extract/ juice. Do not try berries or fruits with a deep color. Fruit color can prevent observation and determination of test results. Discoloration of fruits is not possible with simple methods.

The reason that we will test both immature and well developed fruits is that other reports have shown that fruits gradually lose their starch as they mature. A ripe fruit may have no starch at all.

• Collect samples of fresh fruits that you want to test.
• Wash the fruits and peel the skin off only if you have to.
• Use a juicer to make the juice. If you don’t have a juicer, first use a grinder to shred the fruit; this will create some juice. Additional juice may be obtained by squeezing the shredded fruit in a clean cotton cloth. Make sure the juice is as clear as possible.
• Transfer the extracted juice to a test tube and label the tube with the name and type of the fruit. For example you may use labels such as “ripe apple” or “unripe apple”. For best results, all the test tubes must have the same amount of juice. About 5 milliliter of juice in each tube is a good amount.
• In a separate cup make a 1% solution of corn starch. Get two test tubes and to each test tube add 5 milliliter of the starch solution you just made. Label one tube as starch; label the other tube as control.
• Do nothing with the control tube; but, to all other tubes add five drops of iodine solution each.
• Swirl each tube and look for any color change to blue or black.Change of color to blue, dark blue or black indicate the presence of starch.Record the results in your results table. If your fruit juice is yellow, then the blue color may appear as green.

This is a sample results table:

Place only one X in each row (for each sample) according to your observation.

• The actual number of rows in your results table depend on the number of fruits you choose to test.
• No color change means no starch.
• 5 milliliter is about one spoonful liquid.

Warning: Be sure to throw away the things you test, to be sure that no one accidentally eats any of the iodine.

Experiment 2:

Testing fruits for starch

Introduction: Often farmers and producers of fruits need to test the fruit for presence of starch. Unripe fruits often have a high amount of starch, so they don’t taste good and they are not acceptable to the market. Farmers check the amount of starch in a few samples of fruits and then use the results to estimate when their produce will be ready for market. This is important because farmers need to plan in advance for their harvest time. They need to find customers, rent trucks, hire workers and reserve cold storage space for their produce. In this experiment we will test the fruits the same way as the farmers do. This test is very popular for apple. The following is a chart for testing apple for starch.

Farmers use a chart like this to test the fruit maturity, ripening and determining harvest date. To get the best results for this experiment, you must have access to unripe fruits. (Fruits lose their starch as they ripen.)

Use a shallow glass pan. Pour some iodine solution into this pan to a depth of 5-8 mm. Cut each fruit sample in half. Soak the cut surface of the fruit in the iodine solution for one minute. Remove the fruit from the test solution and place them cut surface up to drain. Score each fruit by the ratio of the cut surface changed to blue or black. For example score 0 if you have no blue or black. Score 10 if all the cut surface is blue or black. Score 5 if about half of the cut surface is changed to blue or black. Note: This experiment is great if you have access to an apple tree or any other tree and can get samples and repeat this test as the fruits grow towards maturity. By recording the test dates you can determine how long does it take for the fruit to lose all its starch.

More information (for higher grades):

The single best measure of determining apple maturity for storing apples is the starch pattern that develops in the fruit. Fruit firmness, soluble solids (sugar) levels, and skin color are all important factors in determining the eating quality and/or salability of apples. When the apple goes toward maturity, the starch molecules break down to sugar molecules.

A solution of iodine and potassium iodide (Iodine Solution) is used to make the starch turn black, and this pattern is the basis for the test. Over the years charts have been developed for many varieties of apple.

Predicting Harvest Date Windows for Apples Full-color plates show how to use and interpret the starch-iodine test for determining maturity and the best harvest dates for quality; especially important for apples going into storage.

Iodine is a very poisonous chemical. The iodine solution should be properly labeled and kept away from children and pets. Apples used in the test should not be fed to any animals or used in composting. In case of ingestion of either iodine or iodine-treated apples, induce vomiting and consult a physician immediately.

Starch is a polymer of glucose, also known as dextrose. The standard test for the presence of starch in juice is the iodine test. In the presence of starch, iodine will form a characteristic blue-violet color. A negative test by iodine indicates that all of the starch has been reduced to a chain length of less than nine to twelve glucose units, a size sufficiently reduced that it will not produce post-bottling hazes. The starch test consists of adding a drop of I 2 KI (iodine solution) to the sample to be tested. If the iodine retains its yellow-brown color, starch is absent …

Experiment 3:

Identify Counterfeit Bills

Most stores test large bills with a special pen, to see if they are counterfeit. The ink in these pens is really the iodine solution; so, all they are doing is testing the paper for starch. The fact is that all papers used for printing or copying contain starch; but, the paper used in making currency has no starch.

You can do the same test using the iodine solution. Use a copy machine to make a copy of a dollar bill. Then test both the dollar bill and the copy that you made by a drop of iodine solution.

Material you need:

• Iodine Solution
• A dollar bill
• Bread or a cracker

Warning! Iodine is poisonous and will stain skin and clothing. Also, some people are allergic to iodine. Be safe and careful.

Use a transfer pipette or a toothpick to put a tiny bit of iodine on a piece of white paper. Notice that the paper turns black. Put a drop of iodine on a piece of bread or cracker and it will also turn black. This is an indicator test. Iodine turns black when it comes in contact with starch. Most paper contains starch and will turn black with iodine.

Now put a drop of iodine on a dollar bill. It stays a brownish color. The special paper used from printing U.S. money does not contain starch, which is one of way that you can spot a counterfeit bill.

You might also try testing different kinds of paper, to see if you can find any others that are starch-free. Any of you that are outside the U.S., can check to see if the bills from other countries are starch-free too.

If you are doing this experiment as a science project you may need to record your results in a table.

Materials and Equipment:

Get Iodine solution

The most important substance that you need for your experiments is iodine solution.

Iodine solution may be purchased online or from a local pharmacy. Following are two of the online stores you may order iodine solution:

http://shop.MiniScience.com Product code: IODINE_S29

http://www.ChemicalStore.com Product Code: IODINE_S29

If you are ordering online, don’t wait until the last minute. Shipping charges are much less when you have enough time for your order to arrive.

Other possible options for iodine solution:

To test a food or other material for presence of starch, you need an Iodine solution. Iodine solution may be available at your local pharmacy in the form of Iodine Tincture. Iodine tincture is an Iodine solution that also contains alcohol. Iodine tincture is a topical antiseptic for use on superficial cuts, insect bits and bruises. May be diluted with water. Germicide providing germicidal activity against bacteria, fungi, viruses and protozoan. Protective agent for painting baby calf and pig navels following birth.

If you have Iodine tincture, skip the next two paragraphs for preparing Iodine solution and recipe.

Preparing the Test Solution

If you frequently need to use Iodine Solution, it is better to prepare it fresh. Iodine solution is sensitive to light and if you want to keep it for a long time, it should be stored in a dark container. A dark-colored bottle or a clear bottle wrapped in aluminum foil will serve the purpose. Chemicals needed for this test are potassium iodide and iodine crystals. A pharmacist or a chemist can use the following recipe to make up the iodine solution.

1. Dissolve 8.8 grams of potassium iodide in about 30 ml of warm water. Gently stir the solution until potassium iodide is properly dissolved. 2. Add 2.2 grams of iodine crystals. Shake the mixture until the crystals are thoroughly dissolved. 3. Dilute this mixture with water to make 1.0 liter of test solution. Mix them well.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results

Calculations:

If you do any calculations in relation to your experiments, write your calculations in this section of your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find books related to photosynthesis and starch. Look for sections that discuss starch test. List such books as your references. Following are some online references:

Evaluating Maturity of Empire, Idared and Spartan Apples by starch test.

Test foods for starch

Additional Starch Experiments:

http://faculty.ntcc.edu/mhearron/photosynthesis.htm Photosynthesis

http://www.austincc.edu/microbugz/40starch.html Starch Hydrolysis test

http://www.biotopics.co.uk/plants/psfac2.html

http://www.netorder.jp/maker/rakuto/enzyme/applications.index.html

http://www.dr-sanderson.org/9N2.htm

It is always important for students, parents and teachers to know a good source for science related equipment and supplies they need for their science activities. Please note that many online stores for science supplies are managed by MiniScience.

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Lab Experiments to Test for the Presence of Starch When Using Potassium Iodine

How-to Science Experiments for Kids With Iodine and Cornstarch

Potassium iodide and iodine solutions are prime examples of indicators, chemicals used to identify the presence of various substances. Indicators change color when they react to a material -- in iodine and potassium iodide’s case, they react in the presence of starch. Because starch is incredibly common, these experiments with iodide solutions offer an interesting and easy way to learn about the use of indicators at home or in the classroom. Be careful using iodide solutions and do not eat food tested with it: the solutions can stain clothes and skin, and iodine can be poisonous.

TL;DR (Too Long; Didn't Read)

With a solution of potassium iodide, it’s possible to test for the presence of starches in liquids, in foods and in freshly-trimmed plant leaves -- where starches are naturally produced. Keep in mind that iodide solutions are only a qualitative indicator for starches and not a quantitative one: they can detect that starches are present, but cannot determine how much starch is present in a given substance.

Testing for Starches

Plants form starches, polymer chains of individual glucose sugar molecules, to store extra energy produced during photosynthesis. Starches come in two forms that both curve into spiral shapes: one long polymer chain known as amylose, or many individual chains attached in branching patterns called amylopectin. Solutions of potassium iodide and iodine form complex iodide ions that, while soluble in water, change color in the presence of starches -- the ions get stuck in the spirals of the starch polymer chains, forcing the iodide ions to become linear and change their electron arrangement. This causes a color change: in the presence of amylose, it becomes blue-black; With amylopectin it becomes a pale purple-red.

Testing in Solids

Before you complete any test for starch, make an iodide solution first. Dissolve 10 grams (0.35 ounces) of potassium iodide and 5 grams (0.18 ounces) of iodine in 100 milliliters (3.4 fluid ounces) of water, then stir. You can use this solution to determine what foods or natural substances contain starches -- place a few drops of the mixture on items such as chicken, potatoes, stones, cucumbers, wood, apples or pears, and watch to see if the solution changes color. If it does, the item contains starch.

Testing in Liquids

Because the complex iodide ions in the solution are soluble in water, use them to test for the presence of starches in liquids as well as in solid items. For this experiment, fill four cups with liquids: two with plain water and two with milk. Dissolve a spoonful of corn starch in one of the water cups and one of the milk cups, then add a few drops of iodide solution to each -- regardless of liquid, the solution will react to the corn starch if it’s present.

Testing for Photosynthesis

You can use an iodide solution to test leaves for starch, and determine whether the plant has performed photosynthesis recently. To do this, put one green-leafed plant in a dark closet, and another on the windowsill where it can receive sunlight. Wait a few days, then take a leaf from each of the two plants: Blanch them in hot water and submerge each leaf in ethyl alcohol until the leaves are colorless. Once the leaves are taken out of the alcohol and placed on dishes, you can use the indicator solution to determine which of the leaves came from the windowsill plant, as only it will turn blue-black.

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• Encyclopaedia Britannica: Starch
• Elmhurst College: Starch-Iodine
• Web Exhibits: Do It Yourself: Starch Test

About the Author

Blake Flournoy is a writer, reporter, and researcher based out of Baltimore, MD. Working independently and alongside professors at Goucher College, they have produced and taught a number of educational programs and workshops for high school and college students in the Baltimore area, finding new ways to connect students to biology, psychology, and statistics. They have never seen Seinfeld and are deathly scared of wasps.

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A collection of experiments that demonstrate biological concepts and processes.

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Testing leaves for starch: the technique, demonstration or class practical.

This procedure kills a leaf, disrupts the cell membranes and softens the cuticle and cell walls. This makes it possible to extract the chlorophyll with hot ethanol and also allows the iodine solution to penetrate the cells and react with any starch present.

Lesson organisation

You can run this as a teacher demonstration, or with students carrying out the procedure in pairs.

Apparatus and Chemicals

For each group of students:.

Eye protection

Beaker for boiling water, 250 cm 3

Boiling tube, 1 for each type of leaf used

Anti-bumping granules (optional)

For the class – set up by technician/ teacher:

Ethanol (IDA) ( Note 1 )

Kettles of boiling water ( Note 2 )

OR Electric water baths set at 90 °C containing a boiling tube rack

Iodine in potassium iodide, solution in dropper bottles ( Note 3 )

Beaker or jar (at least 250 cm 3 ), labelled ‘Waste ethanol’ ( Note 4 )

Leaves, different types, such as pelargonium (pot geranium) ( Note 5 )

Health & Safety and Technical notes

Ethanol (IDA), iodine solution and hot liquids require safety precautions to be taken. Wear eye protection.

Read our standard health & safety guidance

1 Ethanol (IDA) – refer to CLEAPSS Hazcard 40A and student safety sheet 60 – is highly flammable (flash point 13 °C) and harmful (because of the presence of methanol). The risks in this procedure are reduced by using hot water from kettles or in water baths rather than heating with a Bunsen burner flame. Some protocols recommend propanol (Hazcard 84A) in place of ethanol, as it removes chlorophyll more effectively. However, it has the additional risk of eye damage, its flashpoint is very similar to that of ethanol (IDA), and it may be more expensive.

2 Kettles are a safer source of hot water than heating with a Bunsen burner because of the presence of flammable ethanol (IDA) in this procedure. Students are familiar with the hazards of using kettles. Consider how to limit the movement of students around the laboratory with kettles or beakers of near-boiling water. Electrically-heated and thermostatically-controlled hot water baths may be a safer alternative.

3 Iodine solution – refer to CLEAPSS Hazcard 54B and Recipe card 39. A 0.01M solution is suitable for starch testing. Make this by 10-fold dilution of 0.1M solution. Once made, the solution is a low hazard but may stain skin or clothing if spilled, and may irritate the eyes.

4 Save the waste ethanol as a source of chlorophyll for future work. Make sure it cannot be tipped over and is in a safe place so it is not a fire hazard.

5 If the teacher or technician snips the leaves from the plants to give to the students, the plants are more likely to survive to be used again. Variegated Pelargonium (pot geranium) are good subjects for this experiment as are Tradescantia and Impatiens (busy lizzie).

6 Ensure that the plants have been well-illuminated for 24-48 hours. In winter, it might be worth using a halogen lamp to ensure the illumination is adequate.

Ethical issues

There are no ethical issues associated with this procedure.

SAFETY: Ensure the ethanol is kept away from naked flames. Students should wear eye protection when working with ethanol or iodine solution. Take care with hot liquids. Be aware that plant sap may irritate the skin.

Investigation a Collect leaves from the plants to be tested.

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Detecting starch in food on a microscale

In association with Nuffield Foundation

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Test different foodstuffs for the presence of starch using iodine in this microscale class practical

In this experiment, students conduct qualitative tests to find out whether different foodstuffs contain starch. Working on a microscale, students produce iodine in situ by adding potassium iodide crystals and sodium hypochlorite solution to small samples of various foods. They then note any colour change to blue-black, indicating that starch is present.

A quick and easy class experiment. It should be possible to test a range of foodstuffs in about ten minutes.

• Eye protection
• Clear plastic film (eg acetate sheet as used for an overhead projector)
• Forceps (for handling foodstuffs)
• Paper towels
• Sodium hypochlorite solution, 5% w/v of available chlorine (IRRITANT), 10 cm 3
• Potassium iodide crystals, allow 5–10 small crystals per group
• A range of foodstuffs, broken into small pieces, to include both starchy and non-starch-containing foods

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection throughout.
• Sodium chlorate(I) solution (sodium hypochlorite), NaOCl(aq), (IRRITANT at concentration used) – see CLEAPSS Hazcard HC089 . Note this is NOT sodium chlorate(V), NaClO 3 . Sodium chlorate(I) solution can be purchased as such from chemical suppliers. However domestic chlorine-containing bleach solution is quite adequate for this experiment, preferably a cheap brand containing no added detergent or perfumes. Household ‘bleaches’ based on peroxide are becoming more widely available and do not contain chlorine; they should therefore not be used. The sodium chlorate(I) solution should be provided in such a way that students can add a single drop using a plastic dropping pipette. Plastic dropper bottles of capacity 30–60 cm 3 would be suitable for this purpose.
• Potassium iodide crystals, KI(s) –  see CLEAPSS Hazcard HC047b .

It is worth pre-testing the foodstuffs to check that they test correctly – that is, the starchy foods contain enough free starch to give a clear positive test, and the non-starchy foods have not been contaminated by starch-containing material. Note that the amount of free starch present in some uncooked foods may be small, and the test may work more reliably on cooked food.

Suggestions for foodstuffs for testing:

• Place a small piece of each of the foods to be tested on the plastic sheet.
• Place a small potassium iodide crystal on top of the piece of food.
• Add one drop of bleach solution (sodium hypochlorite solution) and allow it to run over both crystal and food.
• If an intense blue-black colour is seen, the food contains starch.
• Clean the plastic sheet with a moistened paper towel.

Teaching notes

The chlorine available from the bleach solution reacts with potassium iodide to form potassium chloride and iodine. The iodine then forms an intense blue-black coloured complex with any starch present. If starch is not present, only the brown colour of iodine in the presence of iodide ions will be seen. The nature of the coloured complex is beyond the level of the students, but note that it is an unstable substance from which the iodine can be easily removed by, for example, sodium thiosulfate.

Each group can be allocated a selection from the range of available foodstuffs, perhaps two starchy foods, and two non-starchy. The class results can then be pooled.

Additional information

This is a resource from the  Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry. This collection of over 200 practical activities demonstrates a wide range of chemical concepts and processes. Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures. Practical Chemistry activities accompany  Practical Physics  and  Practical Biology .

© Nuffield Foundation and the Royal Society of Chemistry

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Practical Science

Table of Contents

Exploring Photosynthesis Variables: A Comprehensive Leaf Starch Test Experiment

Introduction:.

Delve into the fascinating world of plant biology with this comprehensive practical experiment, designed to test the effects of different variables on the rate of photosynthesis in leaves. Photosynthesis, the process by which plants convert sunlight, carbon dioxide, and water into glucose and oxygen, is vital to life on Earth. By modifying variables such as light exposure and carbon dioxide availability, we can observe how these factors impact starch production in leaves and gain a deeper understanding of the factors that influence photosynthesis. Uncover the intricacies of plant life and the essential role that photosynthesis plays in the balance of our ecosystem.

Materials and Equipment:

• Fresh green leaves from a plant exposed to sunlight for several hours (Geraniums work best)
• Aluminum foil
• Calcium oxide (quicklime)
• Test tube or boiling tube
• Forceps or tweezers
• Bunsen burner or hot plate
• Ethanol (alcohol)
• Iodine solution
• White tile or ceramic plate
• Safety goggles
• Lab coat or apron

Step-by-Step Method:

• Safety first: Put on your safety goggles and lab coat or apron to protect your eyes and clothing from potential spills.
• Choose a healthy green leaf from a plant that has been exposed to sunlight for several hours, ensuring the leaf has had ample time to undergo photosynthesis.
• Modify the variables: a. Light exposure: Cover a portion of the leaf with aluminum foil, blocking sunlight from that area and preventing photosynthesis. b. Carbon dioxide availability: Place the plant in a container filled with calcium oxide (quicklime) to absorb carbon dioxide, thereby limiting the plant’s access to this essential component of photosynthesis.
• Leave the plant under these modified conditions for a few hours.
• Boil a beaker of water on a Bunsen burner or hot plate. Use the forceps or tweezers to hold the leaf and immerse it in the boiling water for approximately 1-2 minutes. This step will soften the leaf and kill the cells, halting further photosynthesis.
• Carefully remove the leaf from the boiling water using the forceps or tweezers, and then immerse it in a test tube or boiling tube filled with ethanol (alcohol). Ensure the leaf is fully submerged.
• Place the test tube or boiling tube containing the leaf and ethanol in the beaker of hot water. The ethanol will heat up and decolorize the leaf, removing its chlorophyll. This process should take around 5 minutes. Note: Ethanol is highly flammable, so ensure there are no open flames nearby.
• Once the leaf is decolorized, carefully remove it from the ethanol using forceps or tweezers, and rinse it with cold water to remove any residual ethanol.
• Place the leaf on a white tile or ceramic plate, and add a few drops of iodine solution. The iodine will react with any starch present in the leaf, turning it a blue-black color.
• Observe the leaf for any blue-black coloration, which indicates the presence of starch. Compare the areas of the leaf that were exposed to different variables.

Safety and Troubleshooting:

• Always wear safety goggles and a lab coat or apron to protect your eyes and clothing from potential spills.
• Use caution when handling hot equipment and liquids to avoid burns.
• Ethanol is highly flammable, so ensure there are no open flames nearby when heating the ethanol.

Test Questions:

• What are the two variables being tested in this experiment, and how are they modified?
• Why is it important to cover a portion of the leaf with aluminum foil during this experiment?
• How does calcium oxide affect the rate of photosynthesis in the plant?
• What conclusions can you draw from the blue-black coloration observed in different parts of the leaf?
• Why is it important to study the effects of different variables on the rate of photosynthesis?

Answer Key:

• The two variables being tested in this experiment are light exposure and carbon dioxide availability. Light exposure is modified by covering a portion of the leaf with aluminum foil, and carbon dioxide availability is altered by placing the plant in a container filled with calcium oxide.
• Covering a portion of the leaf with aluminum foil is important because it blocks sunlight from that area, preventing photosynthesis from occurring and allowing us to observe the effects of light exposure on starch production.
• Calcium oxide absorbs carbon dioxide, limiting the plant’s access to this essential component of photosynthesis, and thus affecting the rate of photosynthesis in the plant.
• The blue-black coloration observed in different parts of the leaf indicates the presence of starch, which is a product of photosynthesis. Comparing the coloration in areas exposed to different variables helps us understand how these factors impact the rate of photosynthesis and starch production.
• Studying the effects of different variables on the rate of photosynthesis is important because it helps us understand how environmental factors can influence plant growth and productivity, which has implications for agriculture, ecosystems, and climate change.

By conducting this practical experiment, students can gain valuable insights into the factors that affect photosynthesis and explore the significance of these variables in plant biology. This hands-on approach encourages curiosity and appreciation for the natural world while reinforcing key scientific concepts.

Discovering Photosynthesis: Testing a Leaf for Starch – A Hands-On Practical Experiment

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School Science/Testing leaves for starch

Testing leaves for starch

Introduction

In a food chain, plants are usually the producers, which means they can make food by themselves. They make food by carrying out photosynthesis, then storing the food made in the form of starch.

The aim of the experiment is to compare a covered part of a leaf to an uncovered part of a leaf to see whether plants produce starch

• Water 200 ml
• Boiling water any amount that doesn't exceed 600 ml
• Ethanol 5 ml
• Iodine solution 3 drops
• Safety Goggles
• Bunsen burner
• forceps or tweezers

Safety precautions

• Wear safety goggles
• Keep ethanol away from Bunsen burner; ethanol is flammable
• Tie the hair back
• Tuck ties, files and loose material away
• Keep all bags out of the way to avoid tripping up.
• Make sure you are not wearing tight clothes
• Use the forceps to place the leaf in the boiling water
• Arrange the apparatus as shown in the figure.
• Place a beaker of hot water in the hot water bath. When the water has boiled add the leaf that had been in light.
• Wait 3 minutes for the leaf to boil (this is to get rid of the waterproof layer and break the open cells and make it soft).
• Take out the leaf using the forceps.
• soak it in the ethanol and the water.
• Put the leaf in a boiling tube and cover with ethanol.
• Put the tube of ethanol plus leaf into the beaker of hot water WITHOUT the bunsen burner on as ethanol is highly flammable.
• Dip the leaf back into the hot water, using the forceps.This is done to get the ethanol off the leaf.
• Spread the leaf out on the tile using the glass rod. Add about five drops of iodine solution on to the leaf and observe.
• Carefully draw a diagram of the leaf marking any areas that have stained black.

From this experiment, you will discover that leaves contain starch in the black parts of the leaf. But originally where the green parts of the leaf were present starch is available in lesser quantity..

• Book:School Science