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Chemistry Question on Acids and Bases

Acetic acid dissociates 1.3%. What will be the pH of N10\frac {N}{10} solution of the acid.

A

2.886

B

2.066

C

1.3

D

2.086

Answer

2.886

Explanation

Solution

CH3COOH⇌CH3COO−+ H+ (weak acid) C00 (initially) C(1−α)CαCα (at equilibrium)\begin{matrix}CH_{3}COOH&\rightleftharpoons&CH_{3}COO^{-}&+\,H^{+}\,\left(\text{weak acid}\right)\\\ C&&0&0\,\left(\text{initially}\right)\\\ C\left(1-\alpha\right)&&C\alpha&C\alpha\,\left(\text{at equilibrium}\right)\end{matrix}
Given, concentration (C)=N10\left(C\right)=\frac{N}{10}
degree of dissociation (α)=1.3100\left(\alpha\right)=\frac{1.3}{100}
[H+]=\left[H^{+}\right]= Concentration (C)×\left(C\right) × degree of
dissociation (α)\left(α\right)
[H+]=1.3100×110=1.3×10−3\left[H^{+}\right]=\frac{1.3}{100}\times\frac{1}{10}=1.3 \times 10^{-3}
Thus, pH=−log[H+]pH=-log\left[H^{+}\right]
=−log(1.3×10−3)=-log\left(1.3 \times 10^{-3}\right)
=−log(0.0013)=-log\left(0.0013\right)
=−(−2.88)=2.88=-\left(-2.88\right)=2.88