10tpts-chemistry & acids?
Hydrocyanic acid is a very weak acid. write an equilibrium expression for the ionization of 0.1mol/L HCN(aq). Include the percent ionization @ SATP. Then, calculuate the concentration of hydrogen in it.
please show steps, thanks in advance :)
Update:ka=6.2 x 10^-10
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Queeen,
HCN(aq) = H^+(aq) + CN^-(aq)
Ka = [H^+]*[CN^-]/[HCN] = 6.2 x 10^-10
If we start with 0.1 M HCN, and it dissociates by x, then x of H+ and x of CN- form, so
[H^+] = x
[CN^-] = x
[HCN] = 0.1 - x
[H^+]*[CN^-]/[HCN] = x^2/(0.1 - x) = 6.2 x 10^-10
Let's assume that x <<< 0.1; then
x^2/0.1 - 6.2 x 10^-10
x2 = 6.2 x 10^-11; x = 7.8 x 10^-6 (the assumption was good).
Therefore [H^+] = 7.8 x 10^-6
pH = -log[H^+] = -log(7.8 x 10^-6) = 5.1
Hope that helped!
Sorry - I'll need the Ka for the acid. Don't have it at home. Maybe someone else here has a reference table of such?