Gce Model Questions Vol1 2020 Chemistry Question 26

Practice objective / multiple choice question 26 from the 2020 Gce Model Questions Vol1 Chemistry examination.

Gce Model Questions Vol1 2020 Chemistry Objective / Multiple Choice Hard Difficulty
Question 26 GCE_MODEL_QUESTIONS_VOL1 • 2020 • CHEMISTRY • objective

Acid A is a monoprotic carboxylic acid with molecular formula \(\mathrm{C_3H_6O_2}\). A \(0.020\ \text{M}\) aqueous solution of acid A has a measured \(pH\) of \(2.90\) at \(25^{\circ}\text{C}\). Acid B is another monoprotic carboxylic acid, \(\mathrm{C_4H_8O_2}\), with a known \(pK_a\) of \(4.80\). Both acids are reacted separately with excess ethanol in the presence of a catalytic amount of concentrated \(\mathrm{H_2SO_4}\) under identical conditions. Assuming that the rate‑determining step is the protonation of the carbonyl oxygen, which acid will give the faster initial rate of ester formation? Provide a brief justification based on the calculated \(K_a\) values.

Answer Options

A. Both acids give the same initial rate since their \(K_a\) values are equal (~8.5\times10⁻⁵).
Correct Answer B. Acid A (the \(\mathrm{C_3H_6O_2}\) acid) gives the faster initial rate because its \(K_a\) (~8.5×10⁻⁵) is larger than that of acid B.
C. Acid B (the \(\mathrm{C_4H_8O_2}\) acid) gives the faster initial rate because its \(K_a\) (~8.5\times10⁻⁵) is larger than that of acid A.
D. Acid A gives the faster initial rate because its \(K_a\) (~4.8\times10⁻⁵) is larger than that of acid B.
Correct Answer
B
Correct Option:
Acid A (the \(\mathrm{C_3H_6O_2}\) acid) gives the faster initial rate because its \(K_a\) (~8.5×10⁻⁵) is larger than that of acid B.

About This Question

This is Gce Model Questions Vol1 2020 Chemistry Question 26. It is one of the objective questions from the 2020 Gce Model Questions Vol1 Chemistry examination.

Difficulty level: Hard .

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