Please help me answer these chemistry questions :(

Question

1. Calculate the equilibrium concentrations and pH for a 0.20 M proprionic acid, a solution of a weak acid.

Ka = 1.3 x 10^-5

[H+][C3H5O2]

Ka =

_______________

[HC3H5O2]

2. Calculate the equilibrium concentrations and pH for a 0.20 M carbonic acid (weak acid) solution.

Compare the answer to problem 1. Note which has the higher Ka and lower pH.

Ka = 4.2 x 10^-7

[H+][HCO3-]

Ka =

_______________

[H2CO3]

3. Calculate the pH of a 0.34 M HCl solution.

Answer 1

1. Calculate the equilibrium concentrations and pH for a 0.20 M proprionic acid, a solution of a weak acid.

Ka = 1.3 x 10^-5

CH3CH2COOH ==> H⁺ + CH3CH2COO^-

Ka = 1.3x10^-5 = [H⁺][CH3CH2COO^-]/[CH3CH2COOH]

1.3x10^-5 = (x)(x)/0.20

x² = 2.6x10^-6

x = [H⁺] = [CH3CH2COO^-] = 1.61x10^-3 M

[CH3CH2COOH] = 0.20 - 1.61x10^-3 = 0.1984 M

pH = -log [H⁺] = 2.79

2. Calculate the equilibrium concentrations and pH for a 0.20 M carbonic acid (weak acid) solution.

Compare the answer to problem 1. Note which has the higher Ka and lower pH.

H₂CO₃ ==> H⁺ + HCO₃^-

Ka = 4.2x10^-7 = [H⁺][HCO₃^-]/[H₂CO₃]

4.2x10^-7 = (x)(x)/0.20

x² = 8.4x10^-8

x = [H⁺] = [HCO3^-] = 2.9x10^-4 M

[H2CO3] = 0.20 - 2.9x10-4 = ~0.20 M

pH = -log [H+] = 3.5

3. Calculate the pH of a 0.34 M HCl solution.

HCl ==> H+ + Cl- This is a strong acid and ionizes 100% and as such, does not have a Ka.

pH = -log [H+]

pH = -log 0.34

pH = 0.47