One litre each of a Buffer solution is taken in two beakers connected through a salt bridge. Platinum electrode is immersed in each beaker and electrysis is carried out for `10,000` sec. using a current of `9.65` Ampere. The Buffer contain `(1)/(3)` mole each of `Na_(2)HPO_(4)` and `NaH_(2)PO_(4)` Initially. using the given data answer the following.

Given: ltbr. `pK_(a) (H_(3)PO_(4)) = 4, pK_(a) (H_(2)PO_(4)^(-)) = 7 , pK_(a) (HPO_(4)^(2-)) = 10`
`log 2 = 0.3, log3 = 0.48`
`2.303 (RT)/(F) = 0.06 at 298K`
What is `pH` of solution in which reduction taken place during electrolysis.

Options

A. `12.59`
B. `11.91`
C. `13.01`
D. `11.51`

Answer

B

Explanation

In cathode: `K_(eq) = (K_(w))/(K_(3)) = 10^(-4)`
`PO_(4)^(3-) +H_(2)O hArr HPO_(4)^(2-) +OH^(-)`
`rArr pOH = (1)/(2) pK_(b) - (1)/(2)logC rArr pH = 11.91`