1.

What is [H^(+)] in mol/L of a solution that is 0.20 M in CH_(3)CO ON aand 0.10M in CH_(3)CO OH ? K_(a) for CH_(3)CO OH = 1.8 xx 10^(-5).

Answer»

`9.0xx10^(-6)`
`3.5xx10^(-4)`
`1.1xx 10^(-5)`
`1.8xx10^(-5)`

Solution :The given solution is an acidic buffer. Hence, its pH will be
`pH = pK_(a) +log. (["SALT"])/(["ACID"])`
`=-log.(1.8xx10^(-5))+log.(0.20)/(0.10)`
or `-log(h^(+)]=log.(2)/(1.8xx10^(-5))`
or `log.(1)/([H^(+)])=log.(2)/(1.8xx10^(-5))`
or `[H^(+)]=(1.8xx10^(-5))/(2) = 0.9xx10^(-5)M`
`=9xx10^(-6)M`


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