1.

K_(sp) of AI(OH)_3 is 1xx10^(-15) M. At what pH does 1.0xx10^(-3) M AI^(3+)precipitate on the addition of buffer of NH_4 CI and NH_4 OH solution.

Answer»

Solution :`AI(OH)_3 hArr AI+_((aq))^(3+)+3OH_((aq))^(-)`
`[K_(sp)=pAI^(3+)][OH^-]^3`
`AI(OH)_3` precipitates when
`[AI^(3+)][OH^(-)]^3 GT K_(sp)`
`[1xx10^(-3)][OH^(-)]^3 gt 1xx10^(-15)`
`[OH]^3 gt 1xx10^(-12)`
`[OH^-] gt 1xx10^(-4) M`
`[OH^-]=1xx10^(-4) M`
`POH=-log_(10)[OH^-]`
`=-LOG[1xx10^(-4)]=4`
`PH=14-4=10`
Thus, `AI(OH)_3` precipitates at a `pH of 10.`


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