Question

The ratio of volumes of `CH_(3)C O O H`, 0.1 N to `CH_(3) C O O Na`, 0.1 N required to prepare a buffer solution of pH 5.74 is (given : `pK_(a)` of `CH_(3) C O O H` is 4+74 )
A. `10:1`
B. `5:1`
C. `1:5`
D. `1:10`

Answer 1

Correct Answer - D
Suppose volume of 0.1 N `CH_(3)CO OH` solution
= V mL
and volume of 0.1 N `CH_(3)CO OnN`a solution
= x V mL
`CH_(3)CO OH` present in the final solution
`=(0.1)/(1000)xxV ` mol = `Vxx10^(-4)` mol
`CH_(3)CO ON`a present in the final solution
`=(0.1)/(1000)xx x V "mol" = x V xx 10^(-4)` mol
`pH = pK_(a) + log .(["Salt"])/(["Acid"])`
`:. 5.74=4.74+log. (x V xx10^(-4))/(V xx 10^(-4))`
or log x = 1 or x = 10
`:. ` Ratio = V mL : x V mL = 1 : x = 1 : 10