4.2a - Titration of Hydrochloric Acid with Sodium Hydroxide to Form Sodium Chloride

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Experiment Summary

This experiment involves a titration to determine the concentration of sodium hydroxide using a standard solution of hydrochloric acid.

The neutralisation reaction between hydrochloric acid ( $HCl$ ) and sodium hydroxide ( $NaOH$ ) forms sodium chloride ( $NaCl$ ) and water.
The endpoint of the titration is detected using a methyl orange indicator, which changes from yellow to peach/pink.
After determining the endpoint, the titration is repeated without the indicator, and the resulting solution is evaporated to obtain a sample of sodium chloride (common salt).

Materials and Apparatus Required

Chemicals

Standard 0.1 M hydrochloric acid solution
Sodium hydroxide solution (unknown concentration)
Methyl orange indicator
Deionised water

Apparatus

Burette (50 cm³)
Retort stand with clamp
Pipette (25 cm³) and pipette filler
Conical flask (250 cm³)
Beakers (250 cm³)
White tile
Wash bottle
Safety glasses

Safety Precautions

Wear safety glasses throughout the experiment.
Hydrochloric acid is corrosive and can irritate the skin and lungs.
Sodium hydroxide is corrosive and can cause severe burns; handle with care.
Methyl orange is flammable due to its ethanol content; keep it away from open flames.

Method

Rinse the burette, pipette, and conical flask with deionised water.
Rinse the burette with hydrochloric acid and the pipette with sodium hydroxide solution.
Use the pipette to transfer 25 cm³ of sodium hydroxide solution into a clean conical flask.
Add 5 drops of methyl orange indicator to the sodium hydroxide solution in the conical flask.
Fill the burette with a hydrochloric acid solution, ensuring the level is at 0.00 cm³.
Perform a rough titration by adding hydrochloric acid from the burette while swirling the conical flask, until the solution changes from yellow to peach/pink.
Note the volume of hydrochloric acid used (rough titre).
Repeat the titration more accurately by adding hydrochloric acid quickly until near the endpoint, then add dropwise until the colour change is permanent.
Record the volume of acid used.
Perform a third titration to ensure two readings are within 0.1 cm³ of each other.
Calculate the concentration of sodium hydroxide.

To Obtain a Sample of Salt:

Repeat the titration without adding an indicator.
Evaporate the solution gently until all water is removed, leaving a sample of sodium chloride.

Results

Measurement	Value
Rough titre	24.2 cm³
Second titre	24.1 cm³
Third titre	24.2 cm³
Average of accurate titres	24.15 cm³
Volume of sodium hydroxide solution	25.0 cm³
Concentration of hydrochloric acid	0.1 M
Calculated concentration of NaOH	0.097 M

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Sample Calculation

Using the formula:

\text{VA} \times \text{MA} \times n_B = \text{VB} \times \text{MB} \times n_A

24.15 \times 0.1 \times 1 = 25.0 \times \text{MB} \times 1

MB = \frac{24.15 \times 0.1}{25.0} = 0.0966 \, \text{M}

Therefore, the concentration of sodium hydroxide is 0.097 M.

Example Questions with Answers

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Q1: Describe the washing/rinsing procedure for the apparatus before starting the titration.

Rinse the burette, pipette, and conical flask with deionised water.

Rinse the burette with hydrochloric acid and the pipette with sodium hydroxide solution to avoid contamination.

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Q2: Mention two other precautions to ensure accuracy when using a pipette.

Fill the pipette exactly to the calibration mark.
After releasing the contents, touch the tip of the pipette to the inside of the conical flask for a few seconds to ensure all liquid is transferred.

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Q3: Mention three operations to ensure an accurate titre during titration.

Swirl the conical flask after each addition of acid.
Wash down the sides of the conical flask with deionised water.
Take all burette readings at eye level to avoid parallax error.

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Q4: Suggest another suitable indicator for this titration.

Methyl red or phenolphthalein could also be used.

To test this, repeat the titration and see if the endpoint is clear and consistent with previous results.

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Q5: Why is it undesirable to put sodium hydroxide into the burette rather than the conical flask?

Sodium hydroxide can crystallize and block the burette tap, leading to inaccurate readings or equipment damage.

a - Titration of Hydrochloric Acid with Sodium Hydroxide to Form Sodium Chloride Simplified Revision Notes for Leaving Cert Chemistry

4.2a - Titration of Hydrochloric Acid with Sodium Hydroxide to Form Sodium Chloride

Experiment Summary

Materials and Apparatus Required

Chemicals

Apparatus

Safety Precautions

Method

To Obtain a Sample of Salt:

Results

Sample Calculation

Example Questions with Answers

Q1: Describe the washing/rinsing procedure for the apparatus before starting the titration.

Q2: Mention two other precautions to ensure accuracy when using a pipette.

Q3: Mention three operations to ensure an accurate titre during titration.

Q4: Suggest another suitable indicator for this titration.

Q5: Why is it undesirable to put sodium hydroxide into the burette rather than the conical flask?

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