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For an aqueous solution of NH_4 CI, prove that [H^+]=sqrt(K_(a).C) |
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Answer» Solution :`NH_4 CI` is a SALT of a strong acid HCI and weak base `NH_4 OH`. `HCI_((aq))+NH_4 OH_((aq)) hArr NH_4 CI_((aq))+H_2O(I)` `NH_(4)^(+)` is a strong conjugate acid of the weak base `NH_4OH` and it has a tendency to react with `OH^-` from water to produce unionised `NH_4OH` shown below. `NH_(4)^(+)+H_2O(I) hArr NH_4 OH_((aq))+H_((aq))^(+)` There is no such tendency shown by `CI^-` and therefore `[H^+] gt [OH^-]` , the solution is acidic and the pH is less than 7. s discussed in the salty HYDROLYSIS of strong base and weak acid. In this case also, we can establish a RELATIONSHIP between the `K_n and K_b` as `K_H. K_b=K_w` Let us calculate the `K_h`value in terms of degree of hydrolysis (h) and the concentration of salt `K_h=h^2 C and [H^+]=sqrt(K_h. C)` `[H^+]=sqrt((K_w)/(K_b). C)` `pH=-log[H^+]` `=-log.(K_w. C)/(K_b)^(1/2)` `=-(1)/(2)logK_w-(1)/(2)LOGC+(1)/(2)logK_(b)` `pH=7-(1)/(2)pK_(b)-(1)/(2)logC`. |
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