Question

which of the following solutions has the largest concentration of solvated protons: a) 0.2 M LiOH b) 0.2 M HI c) 1.0 M CH3OH

Answer 1

a) [H+] = Kw /[OH-] = 1 x 10^-14 / 0.2 = 5 x 10^-14 M
b) [H+] = [HI] = 0.2 M (note: HI is a strong acid, thus, [H+] = [HI])
c) pKa of CH3OH = 15,
CH3OH ---> CH3O- + H+
if [H+] = x,
Ka = 1 x 10^-pKa = 1 x 10^-15 = [CH3O-][H+]/[CH3OH] = x^2/(1.0 - x)
since CH3OH is a very weak acid, we can simplify 1.0 - x as 1.0.
So 1.0 x 10^-15 = x^2
x = 3.16 x 10^-8 M

since b > c > a,
b) 0.2 M HI has the largest concentration of solvated protons.

Answer 2

Solvated protons or H3O+ ions are obtained when protons add to water molecules.
Acidic solutions have higher number of dissociated protons. So 0.2 M HI has largest concentration of solvated protons. Methyl alcohol does not dissociatein solution to give protons.