1.

Lemon juice has a pH = 2.1 . If all the acid in lemon is citric acid `(H "Cit." hArr H^(+)+"Cit"^(-1))` and `K_(a)` for citric acid is `8.4xx10^(-4)` mole/litre, what is the concentration of citric acid in lemon juice ?

Answer» Correct Answer - `7.5xx10^(-2)M`
`pH = 2.1 , i.e., - log [H^(+)]=2.1 or log [H^(+)]= - 2.1 = bar(3). 9 or [H^(+)] = 7.943xx10^(-3)`
`"HCit" hArr H^(+) + "Cit"^(-1)`
`K_(a) = ([H^(+)] [Cit^(-1)])/(["H Cit"])`
`8.4xx10^(-4)=(7.943xx10^(-3))(7.943xx10^(-3))/(["H Cit"]) or ["H Cit" ] = 7.5 xx 10^(-2)M`


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