A solution is a homogeneous mixture of two or more substances, with a solute dissolved in a solvent. Water is the universal solvent, dissolving most other substances to form aqueous solutions. The rate at which a substance dissolves, or its solubility, depends on factors like temperature, surface area, movement, and pressure. Higher temperatures increase solubility of solids but decrease gases, while increased surface area, movement, and pressure also generally increase solubility.

1. November 19, 2009 Solutions

2. Objectives Define solution, solubility, insoluble, solute and solvent Name the universal solvent Distinguish between an aqueous solution and a tincture Identify the factors that affect rates of solubility

3. Solution A mixture that appears to be a single substance but is made up of 2 or more substances that are evenly distributed throughout the mixture

4. Characteristics Homogeneous Best mixed of the mixtures Particles are dissolved

5. Solutions are made up of Solutes – the substance that is dissolved Solvents – the substance that does the dissolving. It is always present in greater amount.

6. Solubility – the physical property of being able to dissolve Insoluble – a substance that can not be dissolved

7. Water is the universal solvent. Most things will dissolve in water. It is called an aqueous solution . Sometimes the solvent is alcohol. In this case it is called a tincture .

8. Usually solutions are substances dissolved in a liquid but solutions may also be gasses and solids.

9. Solution rates vary Temperature Surface area Movement Pressure

10. Temperature The solubility of solid solutes in liquid solvents increases with increasing temperature.

11. Temperature The opposite is true of gases. Higher temperature drives gases out of solution. Carbonated soft drinks are more “bubbly” if stored in the refrigerator. Warm lakes have less O 2 dissolved in them than cool lakes.

12. Surface area The larger the surface area of a solid, the faster the rate of dissolving. The surface area of an object increases when it is broken down into smaller pieces.

13. Movement When a substance dissolves, it fills the available spaces between the closest water molecules. Stirring increases the rate the empty spaces can be filled.

14. Pressure The solubility of liquids and solids does not change with pressure. Increased pressure increases the solubility of gases.