1.

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

Answer»

`4.70`
`11.5`
7
6.5

Solution :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`


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