1. Thursday February 23, 2012 (Solutes: Electrolytes and Non-electrolytes)

2. Why does saltwater conduct electrical current but sugar water does not? Saltwater conducts electrical current because water breaks the salt into charged ions, which conduct current. Sugar is broken down into molecules, which do not conduct current.

3. Assignment Currently Open Summativ e or Formative Date Issued Date Due Date Into Grade Book Last Day QUIZ – THE IDEAL GAS LAW AND PHASE CHANGES S2/10 2/24 WS – SolubilityF2/15 QUIZ – SOLUBILITYS2/17 WS – Types of MixturesF2/212/24 WS - Solute – Solvent Interactions F2/222/27

4. Announcements I will be available this afternoon until 4:45.

5. Begin Worksheet Solutes – Electrolytes & Non-electrolytes

6. Solutes: Electrolytes and Nonelectrolytes Substances that dissolve in water are classified according to whether they yield molecules or ions in solution. When an ionic compound dissolves, the positive and negative ions separate from each other and are surrounded by water molecules. These solute ions are free to move, making it possible for an electric current to pass through the solution. A substance that dissolves in water to give a solution that conducts electric current is called an electrolyte.

7. Solutes: Electrolytes and Nonelectrolytes Sodium chloride, NaCl, is an electrolyte, as is any soluble ionic compound. Certain highly polar molecular compounds, such as hydrogen chloride, HCl, are also electrolytes because HCl molecules form the ions H 3 O + and Cl − when dissolved in water. By contrast, a solution containing neutral solute molecules does not conduct electric current because it does not contain mobile charged particles.

8. Solutes: Electrolytes and Nonelectrolytes A substance that dissolves in water to give a solution that does not conduct an electric current is called a non-electrolyte. Sugar is a non-electrolyte. The picture below shows an apparatus for testing the conductivity of solutions.

9. Solutes: Electrolytes and Nonelectrolytes The electrodes are conductors that are attached to a power supply and that make electric contact with the test solution. For a current to pass through the light-bulb filament, the test solution must provide a conducting path between the two electrodes.

10. Solutes: Electrolytes and Nonelectrolytes A non-conducting solution is like an open switch between the electrodes, and there is no current in the circuit. The light bulb glows brightly if a solution that is a good conductor is tested. Such solutions contain solutes that are electrolytes.

11. Solutes: Electrolytes and Nonelectrolytes For a moderately conductive solution, however, the light bulb is dim. If a solution is a poor conductor, the light bulb does not glow at all. Such solutions contain solutes that are non-electrolytes.

12. Complete Worksheet Solutes – Electrolytes & Non-electrolytes