Determine the PH?

determine the PH solution contains 1.0M of HCN ka=6.2*10^-10 and HNO2 kb=4*10^-4?

1 Answer

  • 2 months ago
    Favourite answer

    What you have written as "Kb = 4X10^-4" is actually the Ka for HNO2. Because this acid is 6 orders of magnitude stronger than HCN, any contribution of HCN to the pH of this solution is insignificant and can be ignored.

    HNO2 <--> H+ + NO2-

    Ka = [H+][NO2-]/[HNO2] = 4X10^-4

    Let [H+] = [NO2-] = x and [HNO2] = 1.0 - x. Because Ka is small, initially assume that x will be small compared to 1.0 and can be ignored. Then,

    Ka = x^2 / 1.0 = 4X10^-4

    x = [H+] = 0.02 M

    pH = 1.7

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