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For diprotic selenous acid (H(2)SeO(3)) ...

For diprotic selenous acid `(H_(2)SeO_(3))` equilibrium constants `K_(a)1` and `K_(a)2` are `3.0xx10^(-3) and 5.0xx10^(-8)` respectively. `[OH – ]` of 0.30 M solution of selenous acid is :

A

`2.85xx10^(-3)M`

B

`5.0xx10^(-6)M`

C

`3.3xx10^(-13)M`

D

`3.3xx10^(-12)`

Text Solution

Verified by Experts

The correct Answer is:
C
`K_(s_(1))gt gt K_(a_(2))`, we only consider `I^("st")` ionisation.
`H_(2)SeO_(3)(aq)hArrH_((aq))^(+)+HSeO_(3(aq))^(-)`
`H^(+)'=sqrt(K_(a)xxC)=sqrt(3xx10^(-5)xx0.3)=3xx10^(-2)`
So `[OH^(-)]=(10^(-14))/([H^(+)])=(10^(-14))/(3xx10^(-2))=3.3xx10^(-13)M`
Weak acid and weak base when reacts with each other they acts as strong acid and strong base respectively.
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