In this video we want to discuss the concept of Ionic Product versus Solubility Product. Let's use the dissociation of a sparingly soluble salt calcium hydroxide as an example. Based on the dissociation of calcium hydroxide, solubility product is given as:.
This means K sp measures the maximum amount of ions that the solution can handle or dissolve. Since K sp is an equilibrium constant, it is only affected by changes in temperature, so will be a fixed value at constant temperature. Interestingly ionic product looks exactly the same as solubility product:. However the concentration of ions are for any solution so the solution can be diluted, saturated or supersaturated.
Since ionic product measures the actual amount of ions in solution , it will vary depending on the concentration of ions dissolved. Hence, the concentrations of those ions are raised into 1.
The smaller the solubility product of a substance, then lower the solubility of that substance. That is because solubility product gives how many dissolved ionic species present in that solution. If the amount of ionic species is a little amount, it indicates that the substance is not well-dissolved in that solvent. Then the solubility product is also low value. A major factor affecting the solubility product of a substance is temperature.
When the temperature of a solution is increased, the amount of solutes dissolved in that can be dissolved in that solution is increased; which means, the solubility of a solute is increased. This leads to the increase of solubility product. Therefore, substances have different solubility products at different temperatures. Ionic product and solubility product are two terms that express the same concept of the product of ionic species in a solution.
The difference between ionic product and solubility product is that ionic product is the product of ions in either an unsaturated or saturated solution whereas solubility product is the product of ions in saturated solutions.
Helmenstine, Anne Marie, Ph. Available here 2. Recall that NaCl is highly soluble in water. A The only slightly soluble salt that can be formed when these two solutions are mixed is BaSO 4 because NaCl is highly soluble. The equation for the precipitation of BaSO 4 is as follows:. C We now compare Q with the K sp. The solubility product of calcium fluoride CaF 2 is 3. The solubility product K sp is used to calculate equilibrium concentrations of the ions in solution, whereas the ion product Q describes concentrations that are not necessarily at equilibrium.
The equilibrium constant for a dissolution reaction, called the solubility product K sp , is a measure of the solubility of a compound. Whereas solubility is usually expressed in terms of mass of solute per mL of solvent, K sp is defined in terms of the molar concentrations of the component ions. In contrast, the ion product Q describes concentrations that are not necessarily equilibrium concentrations. Comparing Q and K sp enables us to determine whether a precipitate will form when solutions of two soluble salts are mixed.
Learning Objectives To calculate the solubility of an ionic compound from its K sp. The Solubility Product When a slightly soluble ionic compound is added to water, some of it dissolves to form a solution, establishing an equilibrium between the pure solid and a solution of its ions.
Note As with K , the concentration of a pure solid does not appear explicitly in K sp. Convert the solubility of the salt to moles per liter.
From the balanced dissolution equilibrium, determine the equilibrium concentrations of the dissolved solute ions. Substitute these values into the solubility product expression to calculate K sp. Solution A We need to write the solubility product expression in terms of the concentrations of the component ions.
Answer 4. Calculate the mass of solute in mL of solution from the molar solubility of the salt. Assume that the volume of the solution is the same as the volume of the solvent. Because we are starting with distilled water, the initial concentration of both calcium and phosphate ions is zero.
We can insert these values into the table. Calculate the following: the molarity of a saturated solution the mass of silver carbonate that will dissolve in mL of water at this temperature Answer 1. The Ion Product The ion product Q of a salt is the product of the concentrations of the ions in solution raised to the same powers as in the solubility product expression. The solution is unsaturated, and more of the ionic solid, if available, will dissolve.
The solution is saturated and at equilibrium. The solution is supersaturated, and ionic solid will precipitate. Given: K sp and volumes and concentrations of reactants Asked for: whether precipitate will form Strategy: Write the balanced equilibrium equation for the precipitation reaction and the expression for K sp.
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