Question

Dissociation constant values for \(\text{H}_{2}\text{CO}_{3}\), \(\text{CH}_{3}\text{COOH}\), HCN, and HF are \(4.3\times 10^{-7}\), \(1.8\times 10^{-5}\), \(4.0\times 10^{-10}\) and \(7.2\times 10^{-4}\) respectively, at \(25^{\circ }\text{C}\). Identify the correct order of their increasing acid strength.

• A. \(\text{HF}\lt \text{CH}_{3}\text{COOH}\lt \text{H}_{2}\text{CO}_{3}\lt \text{HCN}\)
• B. \(\text{HCN}\lt \text{H}_{2}\text{CO}_{3}\lt \text{CH}_{3}\text{COOH}\lt \text{HF}\)
• C. \(\text{HCN}\lt \text{HF}\lt \text{H}_{2}\text{CO}_{3}\lt \text{CH}_{3}\text{COOH}\)
• D. \(\text{CH}_{3}\text{COOH}\lt \text{H}_{2}\text{CO}_{3}\lt \text{HF}\lt \text{HCN}\)

Hint:

A larger dissociation constant means a stronger acid, so arrange the Ka values in increasing order.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
A larger dissociation constant \(K_{a}\) means the acid ionises more, so it is stronger.

Step 2: Arrange the values
HCN: \(4.0\times10^{-10}\)
\(\text{H}_{2}\text{CO}_{3}\): \(4.3\times10^{-7}\)
\(\text{CH}_{3}\text{COOH}\): \(1.8\times10^{-5}\)
HF: \(7.2\times10^{-4}\).

Step 3: Order
Increasing acid strength: \(\text{HCN}<\text{H}_{2}\text{CO}_{3}<\text{CH}_{3}\text{COOH}<\text{HF}\).

Final Answer:
The order of increasing acid strength is HCN, H2CO3, CH3COOH, HF. \[ \boxed{\text{(B) }\text{HCN}\lt \text{H}_{2}\text{CO}_{3}\lt \text{CH}_{3}\text{COOH}\lt \text{HF}} \]