Calculate the pH of 0.5 M aqueous solution of NaCN, the `pK_(b) " of " CN^(-)` is 4.70

Options

A. `4.70`
B. `11.5`
C. 7
D. 6.5

Answer

B

Explanation

NaCN is a salt of strong base and weak acid , `pH =7+(1)/(2)pK_(a)+(1)/(2)log C`
`pK_(a) "for " HCN=14-4.70=9.30`
`therefore pH=7+(1)/(2)xx9.30+(1)/(2) log 0.5, pH=11.5`