Gce Model Questions Vol1 2022 Chemistry Question 13

Practice objective / multiple choice question 13 from the 2022 Gce Model Questions Vol1 Chemistry examination.

Gce Model Questions Vol1 2022 Chemistry Objective / Multiple Choice Hard Difficulty
Question 13 GCE_MODEL_QUESTIONS_VOL1 • 2022 • CHEMISTRY • objective

A solution contains 0.050 mol of benzoic acid \( \mathrm{C_6H_5COOH} \) and 0.075 mol of sodium benzoate in 1.00 L of water. The solution is titrated with 0.200 mol dm⁻³ \( \mathrm{HCl} \) until the pH drops to 3.00. (a) Calculate the pH of the original buffer solution (use \(pK_a = 4.20\) for benzoic acid). (b) Determine the volume of \( \mathrm{HCl} \) required to reach pH 3.00. (c) After the addition, calculate the new concentrations of benzoic acid and benzoate, and state which species is now in excess.

Answer Options

A. Original pH = 4.10; HCl volume = 250 mL; [HA] ≈ 0.075 M, [A⁻] ≈ 0.018 M (benzoate in excess)
B. Original pH = 4.55; HCl volume = 400 mL; [HA] ≈ 0.095 M, [A⁻] ≈ 0.0040 M (benzoic acid in excess)
Correct Answer C. Original pH = 4.38; HCl volume = 338 mL; [HA] ≈ 0.088 M, [A⁻] ≈ 0.0055 M (benzoic acid in excess)
D. Original pH = 3.90; HCl volume = 150 mL; [HA] ≈ 0.060 M, [A⁻] ≈ 0.012 M (benzoate in excess)
Correct Answer
C
Correct Option:
Original pH = 4.38; HCl volume = 338 mL; [HA] ≈ 0.088 M, [A⁻] ≈ 0.0055 M (benzoic acid in excess)

About This Question

This is Gce Model Questions Vol1 2022 Chemistry Question 13. It is one of the objective questions from the 2022 Gce Model Questions Vol1 Chemistry examination.

Difficulty level: Hard .

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