Determination Of A Solubility Reaction Lab Report

DETERMINATION OF A SOLUBILITY PRODUCT CONSTANT

Introduction

Parsimoniously soluble ionic solids, when placed in water, go through an equilibrium reaction. This equilibrium reaction is the same as a hypothetical reaction of solid, WxZy as shown in equation 1.

WxZy (s)↔xWy+ + yZx- ………………………………………….. Equation 1

From equation 1, the equilibrium constant (Keq) of any reaction is called Ksp (solubility product constant) of the ionic solid. Fundamentally, solubility product constant is the quantification of the association of the ionic solid and its ions. Ksp is given by:

Ksp= ᵅx[Wy+]ᵅy[Zx-]/ᵅ[ WxZy]……………………….……………... Equation 2

ᵅx[Wy+] and ᵅy[Zx-] represent the ion activities. ᵅx[Wy+] and ᵅy[Zx-] originate from equation 3.

ᵅxWy+=γ Wy+[ Wy+]/A˚……………………..…………………….…

40ml of calcium iodate in water was obtained and placed in a clean labeled beaker. The buret was rinsed and filled with sodium thiosulfate, followed by recording its initial volume. Consequently, 200ml of 0.240M of KI was obtained and poured into a 400 mL beaker. In addition, a clean, dry 250mL Erlenmeyer flask was obtained and 50ml of KI was added into it using a 50mL graduated cylinder. Besides, 10mL of Ca(IO3)2 solution was added to KI solution in a 250mL Erlenmeyer flask using 10.00mL graduated pipette. Finally, 10mL of HCl was added to the solutions of KI and Ca(IO3)2 in a 250Ml Erlenmeyer flask using 10.00mL graduated cylinder. After adding all the solutions, the final of the solutions in a 250mL was brown. The solution was carefully titrated with sodium thiosulfate until it turned yellow. When the solution turned yellow, 10 drops of 1% starch indicator were added to the solution and titration was continued until the solution turned colorless. Final buret reading was recorded and the process repeated once

Though, Ksp values should be the same because the equilibrium that exists between particular solid and its dissolved ions produces a constant Ksp under different conditions. Moreover, other salts such as sodium iodate could be used to produce the same effect as potassium iodate (common ion effect).

The contaminated sodium thiosulfate, potassium iodate, solid calcium iodate and apparatus might have led to experimental errors. The effect of these errors was evidenced when the determined Ksp values were not the same. The dissolution of solid calcium iodate in pure water had Ksp values of 0.01988 and 2.4334 X 10-5 in the first trial and second trial. On the other hand, the dissolution of calcium iodate in potassium iodate solution had Ksp values of 1.6485 X 10-5 and 1.8259 X 10-5 in first and second trials.

When CaCl2 or Ca(NO3)2 solution is added to a solution saturated with calcium iodate, the number of Ca2+ ions would increase in the solution and equilibrium would shift to the side that favors the release of few Ca2+ ions. This is a result of the common ion effect. There are already Ca2+ ions in the