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 amount of acid or salt that should be added to make 90 mL of buffer solution in which if 0.1 mole of strong acid are added into 1 L of this buffer solution then change in pH is unity ?

Options

A. 10 mmoles
B. 22 mmoles
C. 9 mmoles
D. 11 mmoles

Answer

D

Explanation

For buffer capacity of 0.1 we should have `((c+0.1)/(c-0.1))=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=1.1/9`
So, moles required for 90 ml solution =`1.1/9xx90xx10^(-3)` moles =11 m moles