Question

KHT in water

KHT () = K+ (aq) + HT-(aq) Kep = [K+] [HT] K [HT] Initial Foť Change Equilibrium

KHT in KCI

1a. How did the molar solubility of KHT in pure water compare to its molar solubility of KHT in KCl solution? Why?

1b. How did the solubility product constant K_sp of KHT in pure water compare to its solubility product constant K_sp of KHT in KCl solution? Why?

1c. If all the undissolved KHT was not filtered out from the solution prior to titrating, would the calculated molar solubility of KHT be greater or less than the actual molar solubility? Explain.

Answer 1

1a) The molar solubility of KHT in pure water is greater than its molar solubility in KCl solution.

This is because in KCl solution, the dissolution equilibrium shifts in the direction of reactant (undissolved solid) due to the presence of a common ion, Cl- furnished by KCl resulting in decrease in the solubility of KHT. This is called common ion effect.

2b) The solubility product constant of KHT remains same in pure water and KCl solution.

This is because Ksp is an equilibrium constant and equilibrium constants are independent of the initial concentrations of reactants and products. So extra chloride ions furnished by KCl will have no effect on the Ksp value.

3c) If titration is carried out with some solid KHT still remaining in the solution, the molar solubility of KHT increases.

This is because as the titration proceeds, the ions of KHT are removed and hence the dissolution equilibrium now shifts in the forward direction dissolving more of the solid KHT (Le Chatelier's principle). So the calculated molar solubility of KHT will be greater than the actual molar solubility.