1.

Calculate the concentration of hydroxyl ions in 0.2 M solution of ammonium hydroxide having `K_(b) =1.8 xx 10^(-5)`.

Answer» `NH_(4)OH(aq) hArr NH_(4)^(+) (aq) + OH^(-) (aq)`
`K_(b) =[[NH_(4)^(+)(aq)][OH^(-) (aq)]]/[[NH_(4)OH(aq)]]`
For the base, `[NH_(4)^(+) (aq)] = [OH^(-) (aq)]`
`:. " "K_(b) =[[OH^(-) (aq)]^(2)]/[[NH_(4) OH (aq)]]`
` " or "" "[OH^(-) (aq)]^(2) = K_(b) xx [NH_(4)OH(aq) ] = 1.8 xx 10^(-5) xx 0.2 = 3.6 xx 10^(-6)`
`:. " " [OH^(-) (aq)] = (3.6 xx 10^(-6))^(1//2) = 1.897 xx 10^(-3) M`


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