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Experiment 22: Molar SolubilityAbstractThe purpose of this experiment was to determine the molar solubility and the solubility constant of calcium hydroxide. A titrimetric analysis was used, in which moles of hydrochloric acid are added to the basic solution in order to reach the stoichiometric point. From there, the mass action expression was used to determine the solubility constant, and by using Le Chatelier’s Principle, it was possible to predict that adding additional Ca2+ions would shift the equilibrium to the left, and therefore use less acid to titrate the solution. It was calculated that Ca(OH)2 had an average molar concentration of 0.0427 alone, and a molar concentration of 0.023 when Ca2+ions were added. This decrease in molarity in the presence of an ion proved the equilibrium shifted left, leaving a decrease in ions, so the hypothesis was accepted. A compound is considered soluble if it dissolves in water and insoluble if it does not (Tro,2013). Factors such as the pH, additional ions, and temperature can affect the solubility of a compound. If the pH of a solution is high, then there is a high concentration of hydroxide ions present, which proves that the solution is basic (Tro, 2013). When there’s a high concentration ofhydroxide ions the equilibrium will shift to the left and thus lower the solubility (Tro, 2013).
When an ionic compound is added to water, it will dissociate into its respective ions. Compoundsthat dissociate completely are known as strong electrolytes. Compounds that only partially ionizeare weak electrolytes (Tro, 2013). Calcium hydroxide is a slightly soluble salt; slightly soluble salts have very limited solubility in water (Bernan, 2011). Once a slightly soluble salt reaches equilibrium in solution, it is considered to be a saturated solution (Bernan, 2011). However, sincethese types of salts have limited solubility, the saturated solution contains low ion concentrations (Bernan, 2011). When a reaction reaches equilibrium, the mass action expression equals the solubility product, which is the constant K (Bernan 2011). The solubility of a compound is the quantity of the compound that dissolves a certain amount of liquid (Tro, 2013).Whereas the solubility constant can only have one value at a certain temperature solubility itself can have different values (Tro, 2013). When an ion is added to a saturated solution containing slightly