Solubility Equilibrium

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Title: Study of Solubility Equilibrium
The effect of temperature on the solubility product constant, Ksp, of potassium hydrogen tartrate in water was investigated in the temperature range of 285K to 318K at normal atmospheric pressure. It was found that the solubility of potassium hydrogen tartrate decreases with a decrease in temperature and consequently a smaller volume of sodium hydroxide is needed to neutralize it. The molar solubility of potassium hydrogen tartrate was calculated from the volume of sodium hydroxide used. The experimental result for the solubility at 298K was compared to literature data, to verify the reliability of this method. The experimental value is in agreement with the literature data. The values for the solubility product constant at each temperature were obtained from the respective molar solubilities, and fitted to the Van’t Hoff equation. The corresponding enthalpy change for the dissolution is positive and this is consistent with solubility decreasing with decreasing temperature. Introduction

Solubility is the amount of a solute that can dissolve in a given volume of solvent at a given temperature, producing a saturated solution1. A saturated solution refers to a solution that is so concentrated that no more solute that is added will dissolve in it2. Hence an equilibrium exists between the dissolved ions and the undissolved salt3 and the equilibrium constant is the solubility product constant, Ksp. Potassium hydrogen tartrate (KHT) is sparingly soluble in water, and the equilibrium for its dissolution favours the undissolved salt. The dissolution of potassium hydrogen tartrate in water can be represented by the equation below: KHC4H4O6 (s) ↔ K+ (aq) + HC4H4O6- (aq)

It follows that the concentration of HC4H4O6- when the solution is saturated is the molar solubility of KHC4H4O6. The solubility product constant, Ksp, is then determined from the concentrations of the two dissolved ions when the solution is saturated. In...
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