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Ka(1), Ka(2) and Ka(3) are the respectiv...

`Ka_(1), Ka_(2)` and `Ka_(3)` are the respective constants for the following reactions
`H_(2)S hArr H^(+) + HS^(-)`
`HS^(-) hArr H^(+) + S^(2-)`
`H_(2)S hArr 2H^(+) + S^(2-)`
The correct relationship between `Ka_(1), Ka_(2)` and `Ka_(3)` is

A

`K_(a_(3)) =K_(a_(1)) xx K_(a_(2))`

B

`K_(a_(3)) =K_(a_(1)) +K_(a_(2))`

C

`K_(a_(3)) =K_(a_(1))-K_(a_(2))`

D

`K_(a_(3))=K_(a_(1))//K_(a_(2))`

Text Solution

Verified by Experts

The correct Answer is:
A
For the reaction `H_(2)S hArrH^(+) +HS^(-)`
`K_(a_(1))= ([H^(+)][HS^(-)])/([H_(2)S])`
For the reaction `HS^(-) hArr H^(+) +S^(2-)`
`K_(a_(2))= ([H^(+)][S^(2-)])/([HS^(-)])`
When, the above two reactions are added, their equilibrium constants are multiplied.
Thus , `K_(a_(3)) = ([H^(+)]^(2)[S^(2-)])/([H_(2)S]) = K_(a_(1)) xx K_(a_(2))`
Hence , `K_(a_(3))=K_(a_(1))xxK_(a_(2))`
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