Question

A buffer solution is made by mixing a weak acid $HA(K_a={10}^{-6})$ with its salt NaA in equal amounts. what should be the amount of acid or salt that should be added to make 90 ml of buffer solution of buffer capacity 0.1 ?

• A. 10 m moles
• B. 22 m moles
• C. 9 m moles
• D. 11 m moles

Answer 1

The correct option is A 10 m moles

For buffer capacity of 0.1 we should have $\left(\frac{c+0.1}{c-0.1}\right)$ = 10

where c is concentration of weak acid or salt in the buffer solution

So,

C + 0.1 = 10 c - 1

So,

9C = 1.1 or $c=\frac{1.1}{9}$

so moles required for 90 ml solution = $\frac{1.1}{9}\times 90\times {10}^{-3}$ moles = 11 m moles