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Experiment 2: Acid-Base Titration - Determination Of The Concentration Of Hydrochloric Acid Solution

Kolej matrikulasi labuan.

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Experiment 2: acid-base titration – determination of, the concentration of hydrochloric acid solution.

Objectives: i) Prepare a standard solution of oxalic acid. ii) Standardise 0 M NaOH solution. iii) Determine the concentration of HCl solution. iv) Acquire the correct techniques of titration.

Introduction

Titration is a laboratory technique used to determine the concentration of a solution using another solution with known concentration.

Standards in acid-base titrations

In the process of titration, one of the solutions involved serves as a reference standard, which can be categorized as either primary or secondary. A primary standard solution is prepared by precisely dissolving a pure solid with a known molar mass in measured volume of distilled water.

The primary standard solution is utilized to determine the molarity of another standard solution known as secondary standard. For instance, common primary standards like oxalic acid (H 2 C 2 O 4 ) and potassium hydrogen phthalate (KHC 8 H 4 O 4 ) are used to determine the concentration of secondary standards, typically bases.

When performing titrations with NaOH (Sodium hydroxide) solutions, it is necessary to standardize them due to impurities. Solid NaOH is hydroscopic, meaning it absorbs moisture, making it challenging to obtain an accurate mass. After standardization, the NaOH solution becomes the secondary standard and can be employed to determine the concentration of other acids, such as HCl acid.

Equivalence point and end point

During a titration, the equivalence point signifies the stage where the added titrant fully reacts with the electrolyte in accordance with the stoichiometry. To detect this equivalence point, a colour-changing indicator is commonly employed. This indicator’s colour changes the marks the endpoint, which ideally should coincide with the equivalence point.

Chemical equations

In this acid-base titration, the neutralisation reactions involved are:

H 2 C 2 O 4 (aq) + 2NaOH(aq) → Na 2 C 2 O 4 (aq) + 2H 2 O(l) ... (1)

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

Apparatus Chemical Reagents

Burette x M HCl Dropper 0 M NaOH Glass rod Distilled water White tile Phenolphthalein Retort stand Hydrated oxalic acid, H 2 C 2 O 4 .2H 2 O Filter funnel 50 mL beaker 25 mL pipette Analytical balance 250 mL conical flask 250 mL volumetric flask 50 mL measuring cylinder

(A) Preparation of standard solution. 1. Approximately 3 g of hydrated oxalic acid H 2 C 2 O 4 .2H 2 O, was weighted to the nearest 0 g in a 50 mL beaker. 2. About 30 mL of distilled water was added to the beaker to dissolve the oxalic acid. 3. The solution was transferred into 250 mL volumetric flask. The beaker was rinsed, and its contents were poured into the flask. Distilled water was added up to the calibrated mark of the volumetric flask. 4. The flask was stoppered and shaken to obtain homogeneous solution. 5. The concentration of the standard oxalic acid solution was calculated.

NOTE: This solution was used to standardize the NaOH solution in Part (B).

(B) Standardisation of 0 M NaOH solution. 1. The burette was rinsed with the given NaOH solution to be standardized. 2. The NaOH solution was filled into the burette, ensuring that no air bubbles were trapped at the tip. 3. The initial burette reading was recorded to two decimal places. 4. 25 mL of oxalic acid solution from Part(A) was pipetted into a 250 mL conical flask. 2 drops of phenolphthalein were added to the oxalic acid solution. 5. A white tile was placed underneath the flask to allow clear observation of any colour change. 6. The acid was titrated with the NaOH solution from the burette. During the titration, the flask was continuously swirled.

(B) Standardisation of 0 M NaOH solution

Burette reading/ mL Gross I II III

Final reading 24 25 25 24.

Initial reading 0 0 0 0.

Volume of NaOH used / mL 24 24 24 24.

Average volume of NaOH used =

!".!$%!".&$%!".!$ ' 2 8A"45#3>

Calculate the molarity of the NaOH solution.

B8C8DA=EF? # G #8HEDB=EF? # I #HE8C8DA=EF? # G #8B8D=&?#

!"

""#", %", &'(') +",&- ./,, &"",&-0(1'./,, #2 5"7:96#$.

(C) Determination of the molar concentration of HCl solution

Final reading 26 26 25 25.

Volume of NaOH used / mL 25 25 25 25.

!&.($%!&.!$%!&.&$ ' 2 8@"A4#3>

Calculate the molarity of the HCl solution.

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

"!#!

&",&-*./,, &5"7:96$,&8@"a4./,, 2 5"8557#$.

Discussion a) Possible error - Parallax error at the burette. - Air bubble trapped in the burette tip. - Misjudging the colour of the indicator near the end point.

b) Precaution - Take the bottom of the meniscus that aligns with graduated mark at eye level. - Remove air bubbles in the burette tip. - Upon reaching the end point, titrate slowly until a pale pink colour persist for more than 30 seconds.

Conclusion i) The concentration of NaOH solution is J" KLMN#O. ii) The concentration of HCl solution is J" PJJK#O"

• Multiple Choice

Course : chemistry

University : kolej matrikulasi labuan.

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SK015 Experiment 2: Acid Base Titration-Determination of The Concentration of HCl Solution

Acid Base Titration-Determination of The Concentration of HCl Solution. In this experiment, we will prepare standard solution of oxalic acid, and then carry out titration between sodium hydroxide and oxalic acid. Later on, we will carry out titration between sodium hydroxide with hydrochloric acid.

This is the observation you will observe during the end point.

Jotter Video by CraxLab KMPP

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