Question

1. Write the net ionic equation for the reaction that occurs when a solution of hydrochloric acid (HCl) is mixed with a solution of sodium formate (NaCHO2).

2. Calculate the equilibrium constant for this reaction.

3. Calculate the equilibrium concentrations of Na+, Cl?,H+, CHO?2, and HCHO2 when 50.0 mL of 0.35 M HCl is mixed with 50.0 mL of 0.35 MNaCHO2.

Answer 1

For the given reaction

1. net-ionic equation,

HCO2- + H+ ---> HCO2H

2. Keq = 1 x 10^-14/1.8 x 10^-4 = 5.55 x 10^-11

3. HCl = 0.35 M x 50 ml = 17.5 mmol

NaCHO2 = 0.35 M x 50 ml = 17.5 mmol

[CHO2H] formed = 17.5 mmol/100 ml = 0.175 M

CHO2H <==> CHO2- + H+

let x amount dissociated

Ka = [CHO2-][H+]/[CHO2H]

1.8 x 10^-4 = x^2/0.175

x = 5.61 x 10^-3 M

equilibrium,

[CHO2H] = 0.175 - 5.61 x 10^-3 = 0.170 M

[CHO2-] = 5.61 x 10^-3 M

[H+] = 5.61 x 10^-3 M

[Na+] = 0.175 M

[Cl-] = 0.175 M