Questions: Which of the following acids is the weakest? The acid is followed by its Ka value. HNO2, 4.6 × 10^-4 HF, Ka=3.5 × 10^-4 HCN, Ka=4.9 × 10^-9 CH3COOH, Ka=1.8 × 10^-6

Transcript text: Which of the following acids is the weakest? The acid is followed by its Ka value. HNO2, $4.6 \times 10^{-4}$ $\mathrm{HF}, \mathrm{Ka}=3.5 \times 10^{-4}$ $\mathrm{HCN}, \mathrm{Ka}=4.9 \times 10^{-9}$ $\mathrm{CH} 3 \mathrm{COOH}, \mathrm{Ka}=1.8 \times 10^{-6}$

Solution

Solution Steps

Step 1: Identify the given data

We are given the acid dissociation constants ($K_a$) for four different acids:

$ \text{HNO}_2 $: $ K_a = 4.6 \times 10^{-4} $
$ \text{HF} $: $ K_a = 3.5 \times 10^{-4} $
$ \text{HCN} $: $ K_a = 4.9 \times 10^{-9} $
$ \text{CH}_3\text{COOH} $: $ K_a = 1.8 \times 10^{-6} $

Step 2: Understand the relationship between $K_a$ and acid strength

The acid dissociation constant ($K_a$) measures the strength of an acid in solution. A higher $K_a$ value indicates a stronger acid, while a lower $K_a$ value indicates a weaker acid.

Step 3: Compare the $K_a$ values

We compare the given $K_a$ values to determine which is the smallest:

$ \text{HNO}_2 $: $ 4.6 \times 10^{-4} $
$ \text{HF} $: $ 3.5 \times 10^{-4} $
$ \text{HCN} $: $ 4.9 \times 10^{-9} $
$ \text{CH}_3\text{COOH} $: $ 1.8 \times 10^{-6} $

Step 4: Identify the weakest acid

The smallest $K_a$ value corresponds to the weakest acid. Among the given values, $ \text{HCN} $ has the smallest $K_a$ value of $ 4.9 \times 10^{-9} $.

Final Answer

$\boxed{\text{HCN}}$

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