Gce Model Questions Vol1 2021 Chemistry Question 35

Practice objective / multiple choice question 35 from the 2021 Gce Model Questions Vol1 Chemistry examination.

Gce Model Questions Vol1 2021 Chemistry Objective / Multiple Choice Medium Difficulty
Question 35 GCE_MODEL_QUESTIONS_VOL1 • 2021 • CHEMISTRY • objective

Three organic compounds have the following acidities (pK_a values) in water at 25 °C: phenol: pK_a = 10.0; ethanol: pK_a = 16.0; acetylene: pK_a = 25.0. When a mixture of these three compounds is treated with an excess of sodium hydride (NaH), which proton will be abstracted preferentially? Justify your answer by calculating the equilibrium constant for deprotonation of phenol relative to ethanol and of phenol relative to acetylene.

Answer Options

A. Phenol's proton is abstracted preferentially. \(K_{\text{phenol/ethanol}} = 10^{3}\) and \(K_{\text{phenol/acetylene}} = 10^{12}\), so phenol is deprotonated more readily than ethanol or acetylene.
B. Acetylene's proton is abstracted preferentially. \(K_{\text{acetylene/phenol}} = 10^{-15}\) and \(K_{\text{acetylene/ethanol}} = 10^{-9}\), so acetylene is deprotonated more readily than phenol or ethanol.
Correct Answer C. Phenol's proton is abstracted preferentially. \(K_{\text{phenol/ethanol}} = 10^{6}\) and \(K_{\text{phenol/acetylene}} = 10^{15}\), so phenol is deprotonated far more readily than ethanol or acetylene.
D. Ethanol's proton is abstracted preferentially. \(K_{\text{ethanol/phenol}} = 10^{-6}\) and \(K_{\text{ethanol/acetylene}} = 10^{9}\), so ethanol is deprotonated more readily than phenol or acetylene.
Correct Answer
C
Correct Option:
Phenol's proton is abstracted preferentially. \(K_{\text{phenol/ethanol}} = 10^{6}\) and \(K_{\text{phenol/acetylene}} = 10^{15}\), so phenol is deprotonated far more readily than ethanol or acetylene.

About This Question

This is Gce Model Questions Vol1 2021 Chemistry Question 35. It is one of the objective questions from the 2021 Gce Model Questions Vol1 Chemistry examination.

Difficulty level: Medium .

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