acid and base experiment litmus paper

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Acid or alkali? Acidic or alkaline?

In association with Nuffield Foundation

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This simple experiment involves testing a variety of substances to see if they are acidic or alkaline. Litmus paper is used as the indicator

This experiment is most suitable for introductory level chemistry and could be done as a circus with pairs/small groups of students moving from one station to another.

A discussion of the meaning of the words acid, alkali and neutral could be a good way to introduce the experiment. The idea of an indicator should be introduced as a means of distinguishing between the three possibilities, using litmus as the indicator.

• Eye protection
• Watch glasses, 1 per sample (note 1)
• White tiles, 1 per sample (note 1)
• Red and blue litmus paper, 3 pieces of each per working group
• fizzy drinks
• de-ionised/distilled water
• lemon juice

Health, safety and technical notes

• Read our standard health and safety guidance
• Wear eye protection. 
• Provide small amounts of the samples on watch glasses. The watch glasses can be placed on a white tile marked with the name of the substance (use a waterproof marker). The samples can be arranged around the room so that the students visit each in turn. If any solid sample is used, moisten it with a little de-ionised water.
• Check hazard labels on any household substances provided. If this activitiy is set as homework, especially on substances not listed above, pupils should be warned that there are many hazardous chemicals in the home. It is recommended that if chemicals such as bleach, drain clear, or scale remover are to be investigated that this is done by the teacher in school. Thick rubber gloves should be worn if planning to do this due to their hazards.
• Tear each piece of litmus paper into three smaller pieces so that you can test at least nine substances.
• Take one small piece of red litmus paper. Dip it into one of the substances to be tested. Repeat with a small piece of the blue litmus paper.
• Record all observations in a suitable table. Then dispose of the pieces of litmus paper in the waste bin.

Teaching notes

The substance is acidic when:

• the blue Litmus paper turns red and the red Litmus paper is unaffected 

The substance is alkaline when:

• the red Litmus paper turns blue and the blue Litmus paper is unaffected 

If neither red nor the blue paper changes colour, the substance is neutral.

Students should make three lists of substances under the headings ‘acidic’, ‘alkaline’, ‘neutral’.

Encourage the students to use the terms correctly. ‘Acid’ and ‘alkali’ are nouns; the words ‘acidic’ and ‘alkaline’ are adjectives ie ‘A solution of vinegar is acidic. Vinegar is an acid.’

Primary science teaching notes

Skill development.

Children will develop their working scientifically skills by:

• grouping and classifying things
• Recording data and results using scientific diagrams, labels, classification keys and tables
• Using appropriate scientific language and ideas to explain, evaluate and communicate their methods and findings

Learning outcomes

Children will:

• Make predictions and test a variety of substances to determine if they are acidic, alkaline or neutral

Concepts supported

Children will learn:

• Substances can be acidic, alkaline or neutral
• Substances can be grouped according to their properties including whether they are acidic, alkaline or neutral

Suggested activity use

You could carry out this activity as a carousel of different stations, allowing the children to work in pairs or threes to make predictions and then test a range of common everyday substances to see if they are acidic or alkaline. Children can then decide how to record this information and discuss their findings as a plenary activity.

Practical considerations

Various equipment and resources are needed for this practical, including litmus paper and watch glasses.

To get the most out of the activity, children will need some simple understanding of the terms acid (noun), acidic (adjective), alkali (noun), alkaline (adjective), neutral (adjective) and indicator.

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

Health and safety checked, 2016

• 11-14 years
• 14-16 years
• 16-18 years
• Practical experiments
• Acids and bases

Specification

• 8. Investigate reactions between acids and bases; use indicators and the pH scale
• 4. Classify substances as elements, compounds, mixtures, metals, non-metals, solids, liquids, gases and solutions.
• Household acids and bases (two examples of each).
• Self-ionisation of water, Kw;
• The pH scale, from 0 to 14, is a measure of the acidity or alkalinity of a solution, and can be measured using universal indicator or a pH probe.
• A solution with pH 7 is neutral. Aqueous solutions of acids have pH values of less than 7 and aqueous solutions of alkalis have pH values greater than 7.
• Recall that relative acidity and alkalinity are measured by pH.
• 3.3 Recall the effect of acids and alkalis on indicators, including litmus, methyl orange and phenolphthalein
• C6.1.4 recall that relative acidity and alkalinity are measured by pH including the use of universal indicator and pH meters
• C3.3h recall that relative acidity and alkalinity are measured by pH
• pH less than 7
• The pH scale is an indication of the hydrogen ion concentration and runs from below 0 to above 14.
• Acidic solutions have a higher concentration of H⁺(aq) ions than OH⁻(aq) and have a pH below 7.
• Alkaline solutions have a higher concentration of OH⁻(aq) ions than H⁺(aq) ions and have a pH above 7.
• (a) substances as acidic, alkaline or neutral in terms of the pH scale, including acid/alkali strength
• 1.8.2 describe the effects of acidic, alkaline and neutral solutions on indicator papers (red and blue litmus papers and universal indicator paper) and the use of a pH meter to give pH data to at least one decimal place;
• 1.8.1 describe the effects of acidic, alkaline and neutral solutions on indicator papers (red and blue litmus papers and universal indicator paper) and the use of a pH meter to give pH data to at least one decimal place;

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Litmus Paper and the Litmus Test

Litmus paper is pH indicator made by treating filter paper with a solution of litmus. Litmus, in turn, is mixture of dyes made from lichens that changes color in response to acids (red) or bases (blue).

Take a look at the colors litmus paper turns, how to perform and interpret the litmus test, how to make litmus paper, and how the color change works.

Litmus paper is pH paper treated with litmus dye. It can be blue, red, or purple and only changes to those colors. Sometimes people call all pH paper “litmus paper.” But, this is not correct. Many indicators find use as dyes in pH paper and they can change to other colors.

Litmus Paper Colors

There are three varieties of litmus paper: purple, blue, and red. Purple litmus paper contains the dyes used in both blue and red litmus paper.

• Purple Litmus Paper : Purple at neutral pH, red below pH 4.5, blue above pH 8.3
• Blue Litmus Paper : Unchanged blue or sometimes purple at neutral pH, red below pH 4.5, blue above pH 8.3. Blue paper that doesn’t change color indicates the sample is a base.
• Red Litmus Paper : Unchanged red or sometimes purple at neutral pH, red below pH 4.5, blue above pH 8.3. Red litmus paper that doesn’t change color indicates the sample is an acid.

Red litmus paper actually appears more coral-colored than red when dry. It looks deeper red when wet. Blue and purple litmus paper looks slightly darker when wet, but it’s not a big change. Red and blue litmus paper may appear unchanged at neutral pH, but sometimes they lean purple. Red and blue litmus paper don’t necessarily indicate neutral pH.

So, purple litmus paper indicates whether a sample is acidic, neutral, or alkaline. Blue litmus paper indicates whether or not a sample is acidic. Red litmus paper indicates whether a sample is basic.

How to Perform the Litmus Test

The litmus test tells whether a liquid or gas is acidic, neutral, or basic. It indicates whether the substance is pH 4.5 or lower, between 4.5 and 8.3, or 8.3 or higher. The litmus test does not accurately gauge pH — it only tells if the sample is acidic, neutral, or basic.

Litmus Test for Liquids

• Collect liquid sample using a clean dropper or pipette.
• Place a drop of sample on one end of litmus paper test strip. Don’t dip litmus paper into a sample because the dye spreads into it.
• Interpreting the test result depends on the color of litmus paper. In general: red indicates acid, purple is neutral, and blue is basic or alkaline.

Litmus paper that has changed from red to blue may be used as blue litmus paper. Litmus paper that has changed from blue to red may be used as red litmus paper. Used litmus paper isn’t as reliable as a fresh test strip because some residue may remain from the previous test and interfere with results. But, it works fine in most settings and is less wasteful.

Litmus Test for Gases

• Lightly dampen a litmus paper test strip with distilled water. Do not use tap water because it may not have a neutral pH.
• Expose the test strip to the gas.
• If a color change occurs, it affects the entire test strip. Neutral gases, such as nitrogen and oxygen, don’t change the color of litmus paper. Acidic gases turn the paper red, while alkaline gases turn it blue.

Only test water, aqueous samples, or gases using litmus paper. Oil-based samples won’t react with the indicator.

Limitations of the Litmus Test

The biggest limitation of the litmus test is that it gives a rough estimate of pH and not a numerical value. Another limitation is that litmus sometimes changes colors from reactions beside an acid-base reaction. For example, chlorine gas turns blue litmus paper irreversibly white. Basically, it bleaches the dye.

History and Preparation

The word “litmus” comes from an old Norse word for “color” or “dye.” Litmus came into use around 1300 CE by Spanish alchemistry and physician Arnaldus de Villa Nova.

Lichens have been a source of litmus from the 16th century into modern times. Currently, the main sources of litmus are the species Roccella montagnei and Dendrographa leucophoea . Other species producing the pigment include Roccella tinctoria , Roccella fuciformis , Roccella phycopsis , Rocella pygmaea , Ochrolechia parella , Parmotrema tinctorum , Variolaria dealbata , and Parmelia sp . The lichens contain between 10 and 15 indicator compounds. Some of these are separated to act on their own, such as azolitmin and erythrotmin.

The lichens require treatment before becoming litmus. Historically, they were mixed with urine, lime, and potash. After the mixture has fermented, it’s mixed with chalk or plastic of Paris to make blue powder, which can be molded into cakes. Dissolving the dye in water and treating filter paper produces litmus paper.

How the Litmus Test Works

Red litmus is a weak diprotic acid. When exposed to a base, hydrogen ions from litmus react with the base to form the blue conjugate base. The mechanism works in reverse for blue litmus. The blue conjugate base accepts protons from the acid in the test sample, producing the red litmus. At a neutral pH, the process is at equilibrium. Both the red diprotic acid and its blue conjugate base are present, blending to make purple.

Alternatives to Litmus Paper

Coating filter paper with orcein dye or azolitmin dye results in filter paper that behaves much like litmus paper. However, you can coat filter paper with any pH indicator . Universal indicator yields a rainbow of color changes that correspond to numerical pH values. Red cabbage juice is another good choice because it displays a range of colors and is much easier to find at the store than lichens or universal indicator.

• Beecken, H.; E-M. Gottschalk; U. v Gizycki; H. Krämer; D. Maassen; H-G. Matthies; H. Musso; C. Rathjen; Ul. Zdhorszky (2003). “Orcein and Litmus”.  Biotechnic & Histochemistry .  78  (6): 289–302. doi: 10.1080/10520290410001671362
• Musso, H.; Rathjen, C. (1959). “Orcein dyes. X. Light absorption and chromophore of litmus”. Chem. Ber . 92 (3): 751–3. doi:10.1002/cber.19590920331

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Science Projects > Chemistry Projects > Acid Base Reactions & pH Experiments  

Acid Base Reactions & pH Experiments

Experimenting with acids and bases can make for exciting chemistry projects!

Acidic solutions have a higher concentration of hydrogen ions (H+).

These are hydrogen atoms that have lost an electron and now have just a proton, giving them a positive electrical charge.

Basic solutions, on the other hand, contain hydroxide ions (OH-). One of the simplest activities to show how acids and bases react with each other (and to demonstrate their different properties) is to make a vinegar and baking soda volcano .

For another reaction experiment , put an Alka-Seltzer tablet in the bottom of a clear plastic film canister (the kind where the cap fits inside instead of closing over the outside).

Fill the canister with warm water and then quickly put the cap on and watch the acid-base reaction!

The pH scale is used to measure how acidic or basic a solution is. Acids have a pH below 7; bases have a pH above.

Neutral solutions (like distilled water) with a balanced number of H+ and OH- ions have a pH of 7. Do the following projects to explore the cool effects of pH.

Litmus is a natural acid-base indicator extracted from a type of lichen. If you have red and blue litmus paper , you can test different solutions for whether they are acids or bases.

Blue litmus paper turns red when a solution is acidic; red litmus paper turns blue in basic solutions.

Try testing window cleaner, toilet bowl cleaner, orange juice, and apple juice—pour a little of each into separate test tubes or small glasses or jars.

Use the litmus paper to determine which are acids and which are bases. Here are the pH levels of some other substances that you might test:

• Lemon juice (2)
• Vinegar (3)
• Egg whites (8)
• Baking soda (9)
• Ammonia (10)

Human blood has an ideal pH of 7.4; even slight fluctuations can seriously affect our bodies.

You can also make your own pH indicator —use a blender to mix one part chopped red cabbage with two parts boiling water and use the juice to test different solutions.

Acids will turn the pigments in the indicator to a reddish color; bases will turn the pigments bluish or yellow-green.

Mystery Pitcher

Make ordinary water turn bright pink and then back to clear! This makes a great “magic trick” to impress your friends – just be careful no one mistakes it for fruit punch and drinks any!

>> Check out our project video to see this trick in action!

What You Need:

• Phenolphthalein solution
• Sodium carbonate
• 5 glasses and a non-see-through pitcher of water

What You Do:

1. In the first glass put a little less than 1/8 teaspoon of sodium carbonate, in the second put 6 drops of phenolphthalein solution, and in the third put three droppers-full of vinegar.

2. Add a few drops of water to the first glass and stir to dissolve the sodium carbonate.

3. Fill all the glasses with water from the pitcher, then pour all of them back in the pitcher except for the glass with vinegar.

4. Refill the remaining four glasses – the water will be red!

5. Now pour all five glasses back in the pitcher. Refill the glasses one last time—the liquid will be colorless again!

What Happened:

Phenolphthalein is a pH indicator, but it only turns colors in reaction to bases. When you poured the four glasses back into the pitcher, the phenolphthalein reacted to the sodium carbonate, a base, and turned the solution to bright pink “kool-aid.” To change it back to “water,” all you had to do was add the acidic vinegar, which turned the phenolphthalein colorless again.

Rainbow Reaction Tube

Amaze your friends by mixing two solutions to make a rainbow!

Watch as purple sinks to the bottom and red floats to the top, and they mix together to form every color in between.

• 10ml graduated cylinder
• Universal indicator
• Distilled white vinegar

2. Add 3 drops of vinegar to the solution in the graduated cylinder, and it should turn red.

3. In a beaker, put two scoops of sodium carbonate and then add about 30 ml of water. Mix together with the stirring rod until the sodium carbonate dissolves. The solution should be clear.

4. To start the reaction, fill one dropper full with sodium carbonate solution. Squeeze the dropper into the graduated cylinder quickly, rather than drop by drop. The clear solution should instantly turn dark purple, and slowly sink to the bottom, swirling around to make the rainbow.

5. Let the contents of the cylinder settle, until you can see each color from bluish-purple to red. To make the rainbow disappear, pour it into an empty beaker, and it should turn yellow or yellowish green.

Universal indicator changes colors to show the pH level of a substance. In this case, when you mixed an acidic solution (vinegar) with a basic one (sodium carbonate), the indicator made a colorful spectrum — from dark blue to red. Interestingly, if you had added the solutions in the opposite order, you would not have seen a rainbow. To get the rainbow effect, another scientific principle is at work— density . The sodium carbonate solution you made is denser than the indicator solution, so it sinks to the bottom. As the sodium carbonate solution makes its way to the bottom, some of its molecules mix with vinegar molecules, making a new solution, which shows up as a color of the pH scale.

If you don’t turn the graduated cylinder upside down, the rainbow will last several days. Over time the colors will mix together through the process of diffusion. The molecules of each solution will mix throughout the graduated cylinder, rather than staying concentrated at the top or bottom. Once you mix the acid and base solutions together, the solution will be pH neutral, and look yellow or slightly green.

To make a different kind of rainbow tube, try making this rainbow density column with all household materials.

More Chemistry pH Projects:

• Green Eggs & Ham
• Fizzy Bath Bombs
• Acid & Apples
• Copper-Plated Nails

Welcome! Read other Chemistry articles or explore the rest of the Resource Center, which consists of hundreds of free science articles!

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Litmus Paper and the Litmus Test

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You can make paper test strips to determine the pH of an aqueous solution by treating filter paper with any of the common pH indicators. Litmus was one of the first indicators used for this purpose.

Litmus paper is paper that has been treated with a specific indicator—a mixture of 10 to 15 natural dyes obtained from lichens (mainly Roccella tinctoria ) that turns red in response to acidic conditions and blue in response to basic conditions. Pure water shows a neutral pH on litmus paper—it doesn't change the paper's color.

The first known use of litmus was around 1300 AD by Spanish alchemist Arnaldus de Villa Nova. The blue dye on some litmus paper has been extracted from lichens since the 16th century. The word "litmus" comes from the old Norse word for "dye" or "color."

While all litmus paper acts as pH paper, the opposite isn't true. It's incorrect to refer to all pH paper as "litmus paper."

Fast Facts: Litmus Paper

• Litmus paper is a type of pH paper made by treating the paper with natural dyes from lichens.
• The litmus test is performed by placing a small drop of sample onto the colored paper.
• Usually, litmus paper is either red or blue. Red paper turns blue when the pH is basic (alkaline), while blue paper turns red when the pH is acidic.
• While litmus paper is most often used to test the pH of liquids, it can also be used to test gases if the paper is dampened with distilled water before exposure to the gas.

Litmus Test

To perform the test, place a drop of liquid sample on a small strip of paper or dip a piece of litmus paper in a small specimen of the sample. Ideally, don't dip litmus paper in an entire container of a chemical—the dye could contaminate a potentially valuable sample.

The litmus test is a quick method of determining whether a liquid or gaseous solution is acidic or basic (alkaline). The test can be performed using litmus paper or an aqueous solution containing litmus dye.

Initially, litmus paper is either red or blue. The blue paper changes to red, indicating acidity somewhere between the pH range of 4.5 to 8.3 (note that 8.3 is alkaline). Red litmus paper can indicate alkalinity with a change to blue. In general, litmus paper is red below a pH of 4.5 and blue above a pH of 8.3.

If the paper turns purple, this indicates the pH is near neutral. Red paper that does not change color indicates the sample is an acid. Blue paper that does not change color indicates the sample is a base.

Remember, acids and bases refer only to aqueous (water-based) solutions, so pH paper won't change color in non-aqueous liquids such as vegetable oil.

Litmus paper may be dampened with distilled water to give a color change for a gaseous sample. Gases change the color of the entire litmus strip since the whole surface is exposed. Neutral gases, such as oxygen and nitrogen, do not change the color of the pH paper.

Litmus paper that has changed from red to blue can be reused as blue litmus paper. Paper that has changed from blue to red can be reused as red litmus paper.

Limitations

The litmus test is quick and simple, but it suffers from a few limitations. First, it's not an accurate indicator of pH; it doesn't yield a numerical pH value. Instead, it roughly indicates whether a sample is an acid or a base. Second, the paper can change colors for other reasons besides an acid-base reaction.

For example, blue litmus paper turns white in chlorine gas. This color change is due to the bleaching of the dye from hypochlorite ions, not basicity (acidity).

Alternatives to Litmus Paper

Litmus paper is handy as a general acid-base indicator , but you can get much more specific results if you use an indicator that has a narrower test range or that offers a wider color range.

Red cabbage juice , for example, changes color in response to pH from red (pH = 2) through blue (neutral pH) to greenish-yellow (pH = 12). And, while an effective base, you're more likely to find cabbage at the local grocery store than lichen. The dyes orcein and azolitmin yield results comparable to those of litmus paper.

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Litmus Paper Test: Important Acid-Base Indicator

Several plants contain indicators, the most common of which is litmus, which is collected from lichens. It is one of the most basic and earliest pH indicators. In the litmus paper test, if the substance is acidic, blue litmus paper turns red. If the substance is basic or alkaline, red litmus paper becomes blue. In acidic solutions, litmus turns red, and in basic solutions, it turns blue.

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Interesting Science Videos

What Is Litmus Paper?

Litmus Paper is a type of paper that changes color in reaction to the acidity of the solution in which it is dipped and can thus be used to assess acidity. It is a filter paper that has been coated with a natural-soluble color derived from lichen.

Litmus paper is a type of paper that generates a result that may be used to determine the pH of a solution . It is frequently absorbed into filter paper to make one of the oldest kinds of pH indicator, which is used to assess the acidity of materials. Blue litmus paper turns red in an acidic condition, while blue litmus paper turns blue in a basic or alkaline medium.

The color change happens over a pH range of 4.5-8.3 at 25 degrees Celsius (77 degrees Fahrenheit). Under acidic conditions, light blue litmus paper turns red, while red litmus paper turns blue under basic or alkaline conditions. The neutral indication is purple litmus paper.

Arnaldus de Villa Nova, a Spanish alchemist, used litmus for the first time around 1300 CE. Since the 16th century, blue dye has been extracted from lichens. The term “litmus” is derived from the Norse word for “dye” or “color.”

While all litmus paper behaves similarly to pH paper, the contrary is not true. All pH paper should not be referred to as “litmus paper.”

Litmus is mostly obtained from the species Roccella montagnei and Dendrographa leucophoea . Roccella tinctoria, Roccella fuciformis, Roccella phycopsis, Rocella pygmaea, Ochrolechia parella, Parmotrema tinctorum, Variolaria dealbata, and Parmelia sp. are among the other species that produce the pigment. The lichens contain anywhere from 10 to 15 indicator chemicals. Some of these, such as azolitmin and erythrotmin , are separable and act on their own.

Colors of Litmus Paper

Litmus paper comes in three colors: purple, blue, and red. The dyes used in both blue and red litmus paper are present in purple litmus paper.

Purple Litmus Paper: Purple litmus paper remains purple in neutral pH solutions, turns red in acidic pH solutions, and turns blue in basic pH solutions.

Blue Litmus Paper: Blue litmus paper remains unchanging blue or sometimes purple in neutral pH solutions, turns red in acidic pH solutions, and dark blue in solutions with pH greater than 8.3.

Red Litmus Paper: Red litmus paper remains red or sometimes purple in solutions with neutral pH, blue in solutions with basic pH, and dark red in solutions with pH less than 4.5.

When dry, red litmus paper appears more coral-colored than red. When wet, it turns a darker red. When wet, blue and purple litmus paper appear slightly darker, but the difference is minor. At neutral pH, red and blue litmus paper appear unchanged, but they occasionally lean purple. Red and blue litmus paper may not always indicate a neutral pH.

Experiment with Litmus Paper

It is feasible to tell whether a solution is basic or acidic using red and blue test strips or litmus paper, but it is impossible to tell how strong the solution is.

Each number on the pH scale is represented by a different color.

The paper turns green when neutral solutions are employed. Litmus paper is used to determine if a solution is acidic or basic. The litmus paper’s acid or base power is not accurately represented on the paper. Litmus paper is a form of filter paper that has been treated with lichen-derived natural water-soluble pigment.

• Litmus test must be immersed in one of the substances to be tested for contamination. Perform the method a second time using a little piece of blue litmus paper.
• The material tested is acidic if the blue Litmus paper does not change color and the red Litmus paper does not change color.
• This signifies that the material is alkaline if the red Litmus paper turns blue but the blue Litmus paper does not.

Because acids and bases only apply to aqueous (water-based) solutions, pH paper will not change color in non-aqueous liquids like vegetable oil.

To modify the color of a gaseous sample, dampen litmus paper with distilled water. Because the entire surface is exposed, gases alter the color of the litmus strip. The pH paper’s color is unaffected by neutral gases such as oxygen and nitrogen.

Tests for Acids with Litmus Paper

Litmus paper is a natural indication that can be used to assess whether an acidic solution is present. The following actions have to be taken to test the acids with litmus paper:

Step 1: Place the unidentified solution in the beaker.

Step 2: Cut a strip of purple or blue litmus paper, whichever you want.

Step 3: Dip the tip of the purple or blue litmus paper into the appropriate solution.

When the  blue litmus paper turns red, the given solution is acidic.

Tests for Bases with Litmus Paper

Litmus paper is a natural indicator that can be used to determine whether or not a particular answer is fundamental. The following actions have to be taken in order to test the bases with litmus paper:

Step 1: Put the unidentified solution in the beaker.

Step 2: Cut a strip of purple or red litmus paper, whichever you want.

Step 3: Dip the tip of the litmus paper into the appropriate solution.

If the purple or red litmus paper turns blue, the stated solution is simple.

Litmus Paper Use in Chemistry Lab

Litmus paper is a low-cost, portable chemical lab device for testing acidity and alkalinity using only a small volume of solution. The pH of the compounds must be determined.

Other chemical processes beyond acid-base can induce a color shift in litmus paper. For example, chlorine gas turns blue litmus paper white; the litmus dye is bleached due to the presence of hypochlorite ions. Because this reaction is irreversible, the litmus does not serve as an indicator in this situation.

The pH of the material must be tested since most living forms can only live in a narrow pH range, making pH a significant biological indicator. One of the delicate balances is the acid-base balance in the human body. Even a minor change in the pH value of the blood in the body might result in death. Little pH changes in the soil effect not just humans and animals, but also plants.

Limitations

This is why too-acidic soil is tempered with calcium carbonate. The litmus test is quick and easy to use, but it has a few drawbacks. Secondly, it is not an exact pH indicator; it does not produce a numerical pH value. Instead, it tells whether a sample is acidic or basic. Second, the paper’s color can vary for causes other than an acid-base reaction.

Blue litmus paper, for example, turns white when exposed to chlorine gas. This color change is caused by hypochlorite ion bleaching, not acidity/basicity. A base is a fertilizer.

• Beecken, H.; E-M. Gottschalk; U. v Gizycki; H. Krämer; D. Maassen; H-G. Matthies; H. Musso; C. Rathjen; Ul. Zdhorszky (2003). “Orcein and Litmus”.  Biotechnic & Histochemistry .  78  (6): 289–302. doi:10.1080/10520290410001671362
• Musso, H.; Rathjen, C. (1959). “Orcein dyes. X. Light absorption and chromophore of litmus”.  Chem. Ber .  92  (3): 751–3. doi:10.1002/cber.19590920331
• https://unacademy.com/content/ neet-ug/study-material/chemistry/litmus-paper/
• https://tutormate.in/ cbse-class-10-chemistry/indicators-for-testing-acids-and-bases/’
• https://www. scienceequip.com.au/ blogs/news/litmus-paper-everything- you-need-to-know
• https://www.thoughtco.com/what-is-litmus- paper-3976018
• https://byjus.com/ chemistry/litmus-paper/
• Beecken, H.; E-M. Gottschalk; U. v Gizycki; H. Krämer; D. Maassen; H-G. Matthies; H. Musso; C. Rathjen; Ul. Zdhorszky (2003). “Orcein and Litmus”.  Biotechnic & Histochemistry
• https://www.toppr.com/guides/chemistry/solutions/litmus-paper-and-litmus-test/#Litmus_Paper

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• Chemistry Practicals
• CBSE Class 10 Chemistry Practical
• Experiments On Properties Of Acids And Bases

Experiments on Properties of Acids and Base

Table of contents.

• Reaction of Acid and Base
• Reaction of Base with a Metal

Experiment 2A – Reaction of Acid and Base

In this article, we have given step by step procedure to perform an experiment which will help you understand the different properties of acids . Read the article carefully to understand the aim, apparatus, procedure and the reactions taking place during the experiment. You can conduct the experiment and try to match the result with this.

To study the properties of acids (dilute HCl) and bases (dilute NaOH) by their reactions with the following:

• Litmus solution (red/blue)
• Solid sodium carbonate

Materials required:

• Test tube stand
• Test tube holder
• Boiling tube
• Flat bottom flask
• Thistle funnel
• Litmus paper/solution
• Fresh lime water
• Dilute NaOH
• Zinc granules

What is acid?

Chemical species which donate protons or release H + ions when dissolved in water are called acid. They turn blue litmus solution to red colour.

Hydrochloric acid reacts with zinc metal to produce zinc chloride and hydrogen gas. The reaction is given below:

Zn(s) + 2HCl(aq) → ZnCl 2 (aq) + H 2 (g)

Hydrochloric acid reacts with Na 2 CO 3 to produce carbon dioxide and turns the lime water milky as it forms calcium carbonate. The milkiness formed disappears when more than necessary carbon dioxide is passed through the solution. The reaction is as follows:

Na 2 CO 3 (s/aq) + 2HCl(aq) → 2NaCl(aq) + H 2 O(l) + CO 2 (g)

Ca(OH) 2 (aq) + CO 2 (g) → CaCO 3 (s) + H 2 O(l)

CaCO 3 (s) + H 2 O(l) + CO 2 (g) → Ca(HCO 3 ) 2 (aq)

Experimental Setup for Litmus Test Procedure:

• Take a test tube stand and place two test tubes in it.
• Label the test tube as test tube 1 and test tube 2.
• Add 5 ml of blue litmus solution to test tube 1.
• Add 5 ml of red litmus solution to test tube 2.
• Use a dropper and add equal drops of hydrochloric acid in the both test tubes.
• Wait and observe the colour change.

Experimental Setup for Reaction with Zinc metal:

• Take a clean and dry test tube.
• Add zinc granules to it.
• Submerge the zinc granules in the test tube by adding hydrochloric acid to it.
• Close the mouth of the test tube with cork which has a glass delivery.
• A robust explosion takes place between 2-3 minutes liberating colourless and odourless gas.
• When a burning match stick is got near the glass tube mouth the gas burns with a pale blue flame with a pop sound.

2HCl(aq) + Zn(s) → ZnCl 2 (aq) + H 2 ↑

Experimental Setup for Reaction with solid sodium carbonate:

• Take a flat bottom flask with 1 gm of solid sodium carbonate and some distilled water.
• Take a clean and dry double bore cork and thistle funnel which has a delivery tube fitted to it.
• Close the mouth of the flat flask with the double bore cork.
• Add 2 mL of dilute hydrochloric acid.
• Colourless and odourless gas is liberated which is passed through the lime water using the delivery tube.
• The colour of the lime water changes to milky.

Na 2 CO 3 (s/aq) + 2HCl(aq) –→ 2NaCl(aq) + CO 2 ↑+ H 2 O(l)

Ca(OH) 2 (aq) + CO 2 ↑ –→ CaCO 3 (s) + H 2 O(l)

CaCO 3 (s) + H 2 O(l) + CO 2 (g) –→ Ca(HCO 3 ) 2 (aq)

Observation:

Result and Conclusion:

• In the litmus test experiment the blue litmus solution turns red when hydrochloric is added. Therefore, acids such as HCl show acidic character.
• Hydrochloric acid reacts with active metals such as zinc to form zinc chloride and liberate hydrogen gas.
• HCl reacts with sodium carbonate to liberate carbon dioxide gas.

Therefore, from the above three points we can conclude that HCl (Hydrochloric acid) is acidic in nature.

Precautions to be taken during the experiment:

• Conduct the experiment in clean test tubes.
• HCl is corrosive in nature and should be handled with great care.
• Take a small amount of chemicals to perform the experiments.
• While shaking the solution and reaction mixture do not spill.
• Whenever you conduct a test for hydrogen, conduct it with the least amount of gas.
• To get quick results for lime water test, pass carbon dioxide gas through the solution and shake the test tube by placing your thumb on its mouth.

Recommended Videos

Acids and bases.

Neutralization Of Acids And Bases

• When bases dissolve in water which ion do they release?Ans: OH – ions.
• Can you name a metal that reacts with base as well as acid and liberates H 2 gas?. Ans: Zinc metal.
• X releases OH – ions when it dissolves in water. Then X is?Ans: Base.
• Can you write the chemical formula for Zinc chloride?Ans: ZnCl 2 .
• What is the colour of zinc granules when it reacts with HCl?Ans: Black.

Experiment 2B – Reaction of Base with a Metal

What is base.

Chemical species which release OH – ions when dissolved in water are called bases. Sodium hydroxide is a powerful base and has a pH value greater than 7. Therefore, it turns the red litmus solution into the blue.

Sodium chloride reacts with zinc metal to produce sodium zincate and hydrogen gas. The reaction is given below:

Zn(s) + 2NaOH(aq) → Na 2 ZnO 2 (aq) + H 2 (g)

Sodium hydroxide does not react with solid sodium carbonate as both are basic in characteristic.

Na 2 CO 3 (s) + NaOH(aq) → no reaction

Sodium hydroxide neutralizes hydrochloric acid to produce salt (sodium chloride)

NaOH(aq) + HCl(aq) → NaCl(aq) + H 2 O(l)

Experimental Setup for NaOH in Litmus Test:

• Add 3 mL of blue litmus solution to test tube 1.
• Add 3 mL of red litmus solution to test tube 2.
• Use a dropper and add equal drops of sodium hydroxide in both the test tubes.

Experimental Setup for NaOH with Zinc metal:

• Submerge the zinc granules in the test tube by adding sodium hydroxide to it.
• Close the test tube with cork which has a glass delivery tube.
• A robust explosion takes place between 2-3 minutes liberating odourless and colourless gas.
• When a burning match stick is in brought near the glass tube mouth the gas burns with a pale blue flame with a pop sound.

2NaOH(aq) + Zn(s) → Na 2 ZnO 2 (aq) + H 2 ↑

• Take 1 gm of solid sodium carbonate in a test tube.
• With the help of a dropper, put a few drops of NaOH in the test tube.
• No reactions are observed.

• In the litmus test experiment the red litmus solution turns into blue when sodium hydroxide is added. Therefore, bases such as NaOH show basic character.
• Sodium hydroxide reacts with active metals such as zinc to form sodium zincate and liberate hydrogen gas.
• NaOH does not react with sodium carbonate.

Therefore, from the above three points we can conclude that NaOH (sodium hydroxide) is basic in nature.

• NaOH is corrosive in nature and do not heat the mixture of zinc and NaOH to boiling point.
• Take a small amount of chemicals to perform the experiments to get the best results.
• Wash the droppers and test tubes with distilled water before and after using them in the experiment.
• Wash your hands thoroughly after the experiment.
• What happens NaOH comes in contact with red litmus solution?Ans: The red litmus solution turns into blue.
• Which metal other than aluminium reacts with NaOH to produce hydrogen gas?Ans: Zinc metal.
• When CO 2 is passed through the lime water it turns it milky. Why?Ans: The insoluble calcium carbonate makes the solution appear milky..
• Can you write the chemical formula for sodium zincate?Ans: Na 2 ZnO 2 .
• Give examples of strong bases.Ans: KOH. NaOH, etc.

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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What is pH | Acid and base experiment at home | Red and blue litmus paper experiment | pH Paper Test

                  define ph, what is ph, definition of ph, acid and base experiment at home.

Red and Blue Litmus Paper Experiment

Acid and base experiment with litmus paper is the most common tests for acids, bases and neutral solutions or chemicals. These tests can be even performed at home. Litmus paper tests are also known as red and blue litmus paper test. The litmus papers are the chemical indicators used to test the nature of the solution. 

Dip one end of litmus paper in the chemical solution, litmus paper changes its colour as per pH of the solution. Red litmus papers are used to identify basic solution. While, blue litmus papers are used to identify acidic solution.

pH Paper Test

Another most common test for acid and bases is pH paper test. PH papers are used to identify the pH of the chemical substance using pH paper. 

Dip one end of PH paper in the chemical solution, PH paper changes its colour as per pH of the solution.  After 2-3 seconds, remove the paper and compare the colour of the pH paper with the colour chart provided with pH paper kit.

pH Acid Base Test Animation with Litmus Paper Video

Formula for pH Calculation-

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• Student Lab Activities

Using Litmus Paper to Test Acids and Bases

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Litmus paper is commonly used to determine if a solution is acidic or basic. Follow this simple procedure to determine the pH of household chemicals.

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• Litmus Paper

Litmus Paper: An Introduction

As we have learned previously that acids are sour substances and turn blue litmus solution into red litmus solution, whereas, bases are bitter substances and turn red litmus solution into blue litmus solution. But do you know what litmus paper is? How does it turn blue to red or red to blue in colour? How does it respond with acids and bases? In this article, we are going to learn about the litmus paper, its functions, its uses and how it responds with acids and bases.

What is Litmus Paper?

Litmus paper is basically an indicator which is used to distinguish acids from bases as we cannot taste everything to identify if it is an acid or a base . As it indicates the presence of acid or base in a solution, it is also called an acid-base indicator. A litmus paper is made up of wood cellulose paper and litmus. Litmus is a purple dye and it is extracted from lichen plants which belong to the division Thallophyta.

Purple and Blue Litmus Paper

Litmus Paper Colours

Litmus paper is made up of using litmus which is a purple dye but it is available in three different colour varieties which are red litmus paper, blue litmus paper and purple litmus paper.

Red, Blue and Purple Litmus Paper

Purple Litmus Paper:- Purple litmus paper remains purple with the solution having neutral pH, turns red with the solution having acidic pH and turns blue with the solution having basic pH.

Blue Litmus Paper:- Blue litmus paper remains unchanged blue or sometimes purple with the solution having neutral pH, turns red with the solution having acidic pH and turns dark blue with the solution having pH above 8.3.

Red Litmus Paper:- Red litmus paper remains unchanged red or sometimes purple with the solution having neutral pH, turns blue with the solution having basic pH and turns dark red with the solution having pH below 4.5.

Litmus Paper Tests for Acids

Litmus paper is a natural indicator and it can be used to determine whether the given solution is acidic or not. In order to test the acids with the help of litmus paper, the followings steps needed to be followed:

Step-1: Take the unknown solution in the beaker.

Step-2: Take a strip of purple litmus paper or blue litmus paper both are suitable.

Step-3: Now, dip the tip of the purple or blue litmus paper in the respective solution.

If the purple litmus paper or blue litmus paper turns red, then the given solution is acidic.

Blue Litmus Paper Dipped in Acid

Litmus Paper Tests for Bases

Litmus paper is a natural indicator and it can be used to determine whether the given solution is basic or not. In order to test the bases with the help of litmus paper, the followings steps needed to be followed:

Step-2: Take a strip of purple litmus paper or red litmus paper both are suitable.

Step-3: Now, dip the tip of the litmus paper in the respective solution.

If the purple litmus paper or red litmus paper turns blue, then the given solution is basic.

Red Litmus Paper Dipped in Base

Use of Litmus Paper

The main use of a litmus paper is to determine the nature of the given solution. Litmus paper is used to test the acidity or basicity of a solution but, in order to determine the nature of gases, wet litmus powder is used. All litmus paper can act as a pH paper, but all pH paper cannot act as a litmus paper.

Litmus paper is a natural indicator which is used to distinguish acids from bases. It is made up of purple dye which is extracted from lichen plants. Litmus paper is available in three different colours which are purple, red and blue. A purple litmus paper turns red if the given solution is acidic and turns blue if the given solution is basic in nature. In order to test whether the given solution is acidic or basic using litmus paper, take the respective solution in the beaker and dip the tip of the litmus paper in the solution. If the litmus paper turns red, then the solution is acidic, if it turns blue then the solution is basic and if it remains unchanged, then the solution is neutral. The main use of a litmus paper is to distinguish an acid solution from a basic solution.

FAQs on Litmus Paper

1. What are the limitations of a litmus paper?

Although litmus paper is an easy and quick method to test the nature of the substance, it has several limitations and thus, does not fulfil the requirements of a good indicator. Litmus paper can only indicate the nature of the substance i.e. whether it is an acid or a base and does not show the pH which is one of the important factors.

2. Can the litmus paper be reused?

A litmus paper can be reused again. When a litmus paper turns red it can be used as a red litmus paper and when it turns blue, it can be used as a blue litmus paper for testing the substances only when it is completely dried.

3. Is there any substitute for litmus paper?

As a substitute for litmus paper, red cabbage juice can be used to detect the presence of acids or bases. Also, dyes such as orcein and azolitmin are good substitutes for litmus paper.