Solubility of a salt lab answer key

Laboratory 1 Procedure – Concentration, Temperature and the Solubility of Salts

Background:
Solution is a homogeneous mixture of solute and solvent, solution = solute + solvent.

Figure 1. Ionic compound, NaCl salt (solute), dissolved in water (solvent) forming the solution.

In this experiment we will analyze water solutions of ionic compounds, their concentration, and solubility in water.

Concentration, in our case molar concentration, is the amount of solute, expressed in moles, that is divided by volume of the solution, expressed in liters. In the formula bellow, M is a molar concentration, n is a number of moles, and V is a volume of a solution.

M = n/V

Equation 1. Molar Concentration.

Solubility provides information about amount of solute that can be completely dissolved in solvent at given temperature. It is expressed in grams of solute per 100 grams of solvent.

Figure 2 shows the typical representation of the solubility data, that is combined in the plot called temperature and solubility curve.

Figure 2: Temperature and Solubility Curve for Various Ionic Compounds in Water.

This plot can tell us the mass of salt, expressed in grams, that can be dissolved in 100 grams of water at given temperature. There are three types of solutions that are described in this graph:

Unsaturated solution: The solution that does not contain maximum amount of salt that can be dissolved in 100 g of water at given temperature (all the values below the graph line for analyzed salt).

Saturated solution: The solution that contains maximum amount of salt that can be dissolved in 100g of water at given temperature (the values on the graph line for the analyzed salt).

Supersaturated solution: The solution that contains excess of the dissolved salt than could be dissolved by the 100g of water under normal circumstances, temperature, and/or pressure (points above the curve for the analyzed salt).

Temperature and solubility of ionic compounds: Temperature allows to dissolve more solute in 100 g of water, so we say that in most cases solubility of the ionic compounds increases with temperature.