Calcium Hydroxide Essay

SOLUBILITY EQUILIBRIUM OF CALCIUM HYDROXIDE

J.K. DE MATA

NATIONAL INSTITUTE OF PHYSICS, COLLEGE OF SCIENCE

UNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY, PHILIPPINES

DATE PERFORMED: OCTOBER 1, 2015

ABSTRACT

The objective of this experiment is to determine the solubility product constant, Ksp, of Ca(OH)2 through the titration of a saturated solution. This experiment also aims to investigate the factors that influence the changes in the Ksp of a partially soluble ionic compound. Different media of varying conditions were prepared and a 25-mL aliquot from each media was titrated with HCl. Volume used in titration was recorded and was used for the calculations. The graph obtained using the data gathered shows the relationship between

It is also used for reef tanks in saltwater aquaria by making up limewater solutions, and is used as a pH regulating agent. Calcium hydroxide, Ca(OH)2, is an ionic solid that is only slightly soluble in water. A saturated solution of calcium hydroxide has the solid in equilibrium with its ions as shown below.

Ca(OH)2(s) ↔ Ca2+(aq) + 2OH-(aq) (1)

In this experiment, the equation of the Ksp was simplified into

Ksp = [ Ay+]x[Bx-]y (2)

From the expression above, the Ksp of Ca(OH)2 can be written as,

Ksp = [Ca2+][OH-]2 (3) where, [Ca2+] and [OH-] are the equilibrium

Hence, due to the increase attractions between the participating ions, their effective concentrations become lesser causing a considerable increase in its solubility. This effect is governed by the ionic strength given by µ=1/2 ∑_i▒C_i z_i^2 (5) where ci is the molarity of ion and zi as the ion’s charge.

On the other hand, the common-ion effect is an application of the Le Chatelier’s principle which states that when a common ion is added into the solution of dissociated solids, the tendency of the reaction is to proceed towards the precipitation of the dissolved solid. This solution’s shifting equilibrium balances the reaction system in order to attain and maintain an equilibrium state. In this case, the addition on the product side needs to be balanced by formation of the original solid. [1]

This experiment aims to test a saturated solution of calcium hydroxide and calculate the Ksp of the compound.

METHODOLOGY

Table I. Six media at different conditions

Medium Condition

A : 50 mL distilled water : 28º C

B : 50 mL distilled water : 80º C

C : 50 mL distilled water : 10º C

D : 50 mL 0.10 M CaCl2 : 28º C

E : 50 mL 0.50 M KCl : 28º C

F : 45 mL distilled water + 5 mL 95% thanol : 28º