InterviewSolution
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InterviewSolution
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Percentange ionisation of weak acid can be calculated using the formula:A. `100sqrt((K_(a))/(C ))`B. `(100)/(1+10^((pK_(a)-pH))`C. both (a) and (b)D. none of these |
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Answer» Correct Answer - C For weak acid dissociation equilibria, degree of dissociation `alpha` is given as: `alpha = sqrt((K_(a))/(C ))` `:. %alpha = 100sqrt((K_(a))/(C ))` Also `K_(a)= ([H^(+)][A^(-)])/([HA])= ([H^(+)].Calpha)/(C(1-alpha))` `= ([H^(+)].alpha)/((1-alpha))` `log K_(a)= log H^(+)+log (alpha)/((1-alpha))` or `pK_(a)=pH+log(1-alpha)/(alpha)` or `pK_(a)-pH=log (1-alpha)/(alpha)` `:. (1-alpha)/(alpha)=10^(pK_(a)-pH)` or `(1)/(alpha)=10^(pK_(a)-pH)+1` or `alpha=(1)/([1+10^(pK_(a)-pH))]` |
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