The `pH` of `0.1M` monobasic acid is `4.50`. Calculate the concentration of species, `H^(o+), A^(Θ)`, and `HA` at equilibrium. Also determine the value of `K_(a)` and `pK_(a)` of the monobasic acid.

Answer

`[H^(+)]=[A^(-)]=3.16xx10^(-5)M, K_(a) = 1.0xx10^(-8), pK_(a)= 8`

Explanation

`HA hArr H^(+)+A^(-), log [H^(+)] = - pH = - 4.50 = bar(5).5`
`:. [H^(+)]=3.16xx10^(-5)M`
`[H^(+)]=[A^(-)]=3.16xx10^(-5)M`
`[HA]=(0.1-3.16xx10^(-5))~= 0.1M`
`K_(a) = (3.16xx10^(-5))^(2//0.1)=1.0 xx 10^(-8), pK_(a)=8`.