Purify a Given Sample of Sodium Chloride by Passing HCl Gas. (Application of common ion effect)

 Abstract

This experiment aims to purify a given sample of sodium chloride by passing hydrogen chloride (HCl) gas through it. The process involves utilizing the common ion effect to precipitate impurities, leaving behind purified sodium chloride.

Introduction

In this experiment, sodium chloride (NaCl) is purified by passing HCl gas through its solution. When HCl gas is passed through the solution, it reacts with sodium hydroxide (NaOH) and water (H₂O) present in the solution, producing hydrochloric acid (HCl) and sodium hypochlorite (NaOCl). The resulting NaOCl, in the presence of Cl^- ions from HCl, forms NaCl, which precipitates out due to the common ion effect. The precipitate is then filtered to obtain purified sodium chloride.

Experiment Details

Procedure

1. Dissolve the given sample of sodium chloride in distilled water to prepare a solution.
2. Place the solution in a suitable container.
3. Connect a delivery tube from the HCl gas generator to the container containing the NaCl solution.
4. Start passing the HCl gas through the solution slowly.
5. Observe the formation of a white precipitate, indicating the formation of purified sodium chloride.
6. Continue passing the gas until no further precipitate forms.
7. Filter the solution to separate the precipitate from the solution.
8. Wash the precipitate with distilled water to remove any impurities adhering to it.
9. Dry the purified sodium chloride in an oven.
10. Weigh the dried sodium chloride to determine the yield.

Observations and Calculations

The formation of a white precipitate (NaCl) indicates the purification process. The yield of purified NaCl can be calculated by weighing the dried precipitate obtained after filtration.

Conclusion

The purification of sodium chloride by passing HCl gas demonstrates the application of the common ion effect. The precipitation of NaCl from the solution results in the removal of impurities, leading to the isolation of purified sodium chloride.

Precautions

• Handle HCl gas with care as it is corrosive and toxic.
• Use distilled water for preparing the NaCl solution to avoid introducing impurities.
• Ensure proper ventilation in the laboratory when working with HCl gas.
• Wash hands thoroughly after handling chemicals.

Short Questions with Answers

1. What is the common ion effect?
   Answer: The common ion effect is a phenomenon where the solubility of a salt is reduced by the presence of a common ion in the solution.
2. How does the common ion effect help in purifying sodium chloride by passing HCl gas?
   Answer: The common ion effect reduces the solubility of sodium chloride by the addition of chloride ions from HCl gas, leading to the precipitation of purified sodium chloride.
3. Why is the use of distilled water important in the purification process?
   Answer: Distilled water is used to avoid introducing impurities that could interfere with the purification process of sodium chloride.
4. What precaution should be taken when handling HCl gas during the experiment?
   Answer: HCl gas should be handled with care as it is corrosive and toxic. Proper ventilation and protective equipment should be used.
5. Explain the purpose of filtering the solution after passing HCl gas.
   Answer: Filtering is done to separate the precipitated purified sodium chloride from the solution and remove any remaining impurities.
6. How is the purity of sodium chloride confirmed after the purification process?
   Answer: The purity of sodium chloride is confirmed by drying and weighing the precipitate obtained after filtration.
7. What is the role of sodium hydroxide in the reaction with HCl gas?
   Answer: Sodium hydroxide reacts with HCl gas to form sodium hypochlorite and water.
8. Why is it important to wash the precipitate with distilled water?
   Answer: Washing the precipitate removes any impurities or soluble by-products adhering to it, ensuring the purity of sodium chloride.
9. Explain how the common ion effect is utilized in other chemical processes.
   Answer: The common ion effect is used in various chemical processes, such as precipitation reactions, buffer solutions, and pH control in analytical chemistry.
10. What is the significance of drying the purified sodium chloride?
    Answer: Drying ensures the removal of residual moisture and solvents, leading to the isolation of pure sodium chloride in solid form.
11. What safety measures should be followed when working with corrosive chemicals like HCl gas?
    Answer: Safety goggles, gloves, and a lab coat should be worn to protect against splashes. Work in a well-ventilated area or fume hood to minimize exposure to vapors.
12. How does the common ion effect affect the solubility of sodium chloride in the presence of HCl?
    Answer: The presence of chloride ions from HCl reduces the solubility of sodium chloride, leading to its precipitation as a solid.
13. What is the purpose of weighing the dried sodium chloride after purification?
    Answer: Weighing allows for the determination of the yield and purity of the purified sodium chloride.
14. Why is it essential to ensure that no further precipitate forms before completing the purification process?
    Answer: Ensuring no further precipitate forms indicates that all impurities have been removed, resulting in the highest possible purity of sodium chloride.
15. How does the purification process of sodium chloride by passing HCl gas demonstrate the principles of chemical equilibrium?
    Answer: The formation of precipitated sodium chloride represents an equilibrium shift toward the solid phase due to the common ion effect.
16. What role does the concentration of HCl gas play in the purification process?
    Answer: The concentration of HCl gas affects the rate and extent of the reaction with sodium chloride, influencing the efficiency of the purification process.
17. What should be done if impurities are still present after passing HCl gas through the sodium chloride solution?
    Answer: If impurities persist, additional purification steps, such as recrystallization or further filtration, may be necessary to obtain pure sodium chloride.
18. How can the success of the purification process be confirmed visually?
    Answer: The formation of a white precipitate of sodium chloride indicates the successful purification process.
19. What happens if the sodium chloride solution is not filtered after passing HCl gas?
    Answer: Failure to filter the solution may result in the presence of undissolved impurities in the final product, reducing the purity of sodium chloride.

Multiple Choice Questions (MCQs)

1. What is the common ion effect?
   a) A phenomenon where two solutions mix together
   b) The reduction of solubility of a salt by the addition of a common ion
   c) The increase in solubility of a salt by the addition of a common ion
   d) A process to separate ions in a solution
   Answer: b) The reduction of solubility of a salt by the addition of a common ion
2. Why is it important to dry the purified sodium chloride?
   a) To increase its solubility
   b) To remove impurities
   c) To prevent contamination
   d) To reduce its reactivity
   Answer: c) To prevent contamination
3. What is the purpose of filtering the solution after passing HCl gas?
   a) To remove excess HCl gas
   b) To separate impurities from purified NaCl
   c) To increase the concentration of NaCl
   d) To prevent the formation of NaOH
   Answer: b) To separate impurities from purified NaCl
4. Which of the following should be used to weigh the dried sodium chloride?
   a) Plastic container
   b) Aluminum foil
   c) Watch glass
   d) Analytical balance
   Answer: d) Analytical balance
5. What should be done to ensure accurate results in the experiment?
   a) Use tap water
   b) Handle chemicals with bare hands
   c) Measure volumes roughly
   d) Follow the procedure carefully
   Answer: d) Follow the procedure carefully