What is the pH of a 0.50 M aqueous NaCN solution ? pK_(b)of CN^(-) is

1.	What is the pH of a 0.50 M aqueous NaCN solution ? pK_(b)of CN^(-) is 4.70.
Answer» Solution :`NaCN + H_(2)O HARR NaOH + HCN` or `CN^(-) + H_(2)O hArr OH^(-) HCN` `K_(B)=([OH^(-)][HCN])/([CN^(_)])=([OH^(-)]^(2))/([CN^(-)])` `:. pK_(b) = - LOG K_(b) = - 2 log [OH^(-)]+log [CN^(-)]` or `4.70 = - 2 log [OH^(-)]+ log (0.5)`[`:' [CN^(-)]=[NaCN]]` or` 2log [OH^(-)]=-5.00 or log [OH^(-)]=-2.5` `-log [OH^(-)]=2.5` `p_(OH)=2.5` `pH = 14-25 = 11.5`

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