1. SOLUBILITY BASICS

2. Why do things dissolve?  To understand solubility, it is important to understand why things dissolve. Why some things dissolve and some do not?  Intermolecular forces  In process of dissolving, molecules of the solute are inserted into a solvent and surrounded by its molecules.  In order for the process to take place, molecular bonds between molecules of solute (ie. sugar) have to be broken and molecular bonds of the solvent also have to be disrupted. Both of these require energy.

3. Why do things dissolve?  Example of sugar  When sugar dissolves in water, new bonds between sugar and water are created. During this process energy is given off. The amount of this energy is sufficient to break bonds between molecules of sugar and between molecules of water. This example applies to any solute and solvent.  If the bonds between solvent or solute are too strong and there is not enough energy provided while dissolving to break them, the solute will not dissolve.

4. What is Solubility? SOLUBILITY  The ability of a substance to dissolve  In the process of dissolving, the substance which is being dissolved is called a solute and the substance in which the solute is dissolved is called a solvent  A mixture of solute and solvent is called a solution

5. Example  To put it in simple words: When we insert sugar into water it will dissolve. In this process:  sugar is the solute  water is the solvent  One of the characteristics of table sugar is its solubility in water

6. A Chemist’s Understanding of Solubility  SOLUBILITY is understood as a maximum amount of solute that dissolves in a solvent at specific conditions of temperature and pressure.  Such a solution is called a saturated solution.

7. Solubility Facts  Every chemical substance which dissolves in water has a fixed solubility.  If it does not dissolve - its solubility is zero.  Many of these solublities have been measured and special charts are produced displaying solubility of many substances at once.  Remember substances can be identified by their solubility in a specific solvent at specific conditions of temperature and pressure.

8. Solubility Curves  A solution can be saturated, unsaturated or supersaturated.saturatedunsaturated supersaturated  Solubility of a substance refers to the maximum amount of substance that can dissolve in a given volume of solvent at a certain temperature.  We measure solubility of a substance by measuring the maximum mass of solute that can be dissolved in 100 grams of solvent at a given temperature.

9. Solubility Curves  The relationship between solubility and temperature can be expressed by a solubility curve.  The solubility curves of several compounds are shown on the right.  Such curves reveal the maximum amount of solute that can be dissolved in 100 grams of water over a range of temperatures.  The solubility of most compounds increases as temperature increases, although exceptions do exist.

10.  Consider the solubility curves of 4 unknown compounds, shown on the right.  Consider compound "X".  Reading straight from the solubility curve we can see that at 40 o C the maximum mass of substance "X" that can dissolve in 100 grams of water is 62 grams. Temperature 0 C How do we read solubility curves?

11. Let’s Practice  Use the solubility graph below to answer questions on your own paper.