The pH of the mixture when 50 mL each of `0.4M` and `0.1M` of HCI and NaCN each are mixed not necessarily in respective order are: `(pK_(b)of CN^(-)=4.6128 and log 1.5=0.1761 and log 3=0.4771)`

Options

A. `9.8239, 0.8643`
B. `0.5228, 0.8643`
C. `0.8643, 0.5228`
D. `0.8239, 9.8643`

Answer

D

Explanation

(i) `{:(,HCI+,NaCNrarr,NaCI+,HCN),("Mole added", 50xx0.4, 50xx0.1,0,0),(, =20,=5,0,0),("Mole after reaction", 15,0,5,5):}`
`:. pH= -log [H^(+)]= -log(15)/(100)= 0.8239`
(ii) `{:(,HCI+,NaCNrarr,NaCI+,HCN),("Mole added", 5,20,0,0),("Mole after reaction",0,15,5,5):}`
`:. pH= pK_(a)HCN+log(15)/(5)`
`= 14-4.6128+log (15)/(5)=9.8643`