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Experiment 5: Study Of Solubility Equilibrium

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Experiment 5: Study of Solubility Equilibrium

Aim

To determine the solubility product constant Ksp of a sparingly soluble salt potassium hydrogen tartrate (KHC4H4O6) in water To calculate the change in enthalpy (ΔH° reaction) and entropy (ΔS° reaction) of the reaction

Results and Discussion
The dissociation reaction of potassium hydrogen tartrate (KHC4H4O6) in water can be written as: KHC4H4O6 (aq) ⇆ K+ (aq)  HC4H4O6- (aq)

Determination of Ksp at 284 K
The expression of its solubility product constant Ksp is Ksp = [K+] [HC4H4O6¬¬¬] where [K+] and [HC4H4O6] are the concentrations of the dissociated K+ and HC4H4O6 respectively. Since hydrogen tartrate ion behaves as a weak acid, the number of moles of NaOH used in the titration …show more content…

Determination of ΔH and ΔS
Using the plot of lnKsp versus 1/T, the slope of the best-fit equation and the y-intercept was found. Using van’t Hoff equation, the change in enthalpy ΔH and entropy ΔS of the dissolution reaction was found to be 44 ± 1.3 kJ K-1 mol-1 and 89 ± 4 J K-1 mol-1 respectively.
Using van’t Hoff equation, lnK = - (ΔH°reaction)/RT + (ΔS°reaction)/R where ΔH°reaction and ΔS°reaction ¬are the standard enthalpy and entropy change of the reaction respectively.
From Figure 1, the gradient and y-intercept was obtained as shown in Table 4 in the Appendix.
The enthalpy change and entropy change was then calculated.
Gas constant R = 8.3145 J/mol * K = .008314 kJ/mol * K
Gradient = (ΔH°reaction)/R
Gradient = - (/ R) = -5264.95
Standard deviation of gradient: ± 157.84
ΔH°reaction = - (-5264.95 x .008314) ± (157.84 x .008314) = (43.7727± 1.31) kJ K-1 mol-1
ΔH°reaction = 44 ± 1 kJ K-1 mol-1
Intercept = (ΔS°reaction)/R
Y-intercept = (/ R) = 10.759 ± 0.52219
Standard deviation of Y-intercept = ± 0.52219
ΔS°reaction = (10.759 x 8.314) ± (0.52219 x 8.314) = (89.4 ± 4.34) J K-1 …show more content…

The experimental Ksp at 291.15 K was found to be 7.10 x 10-4 + 5 x 10-6 and compared to the literature value of 3.8 x 10-4. Since ΔH° reaction and ΔS° reaction was assumed to be nearly independent of temperature, the change in enthalpy and entropy of the reaction was found using the gradient and intercept respectively of the linear plot of lnKsp versus the reciprocal of temperature. Using van’t Hoff equation, ΔH° reaction and ΔS° reaction was found to be 44 ± 1.3 kJ K-1 mol-1 and 89 ± 4 J K-1 mol-1

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