`pH` of a mixture of `1 M` benzoic acid (`pK_(a)=4.20`) and `1 M C_(6)H_(5)COONa` is `4.5`. In `300ml` buffer, benzoic acid is `[log2=0.3]`

Options

A. 200mL
B. 150 mL
C. 100mL
D. 50 mL

Answer

C

Explanation

`pH =pK_(a)+log.(["Salt"])/(["Acid"])`
`4.5 =4.2 +log .(["Salt"])/(["Acid"])`
`0.3 =log.(["Salt"])/(["Acid"])`
`(["Salt"])/(["Acid"])=`antilog `0.3 =2`
Let`upsilon` mL of 1 M benzoic acid is mixed with `(300-upsilon)` mL of 1M sodium benzoate
`:. (300-v)/(upsilon)=2`
`300-upsilon=2 upsilon`
`upsilon=100mL`