1. CHEM 100 Chemistry and Society Winter Quarter 2008 SCCC Lecture 38 In all the hurry to revise don’t forget to do a good job on lab reports….

2. “What is a solvent? What is the solvent used in most solutions?” A solvent is a liquid that dissolves a chemical compound and is the major part of a solution. The solvent used in most solutions is water.

3. “How could you determine if a solution is saturated or not?” You could tell if a solution is saturated or not by attempting to dissolve more solute. If the extra solute will not dissolve the solution is saturated.

4. “What is the role of spectator ions in a precipitation reaction” Spectator ions undergo no chemical change during a precipitation reaction. They are important though as they balance the charge of the ions being precipitated. A precipitation reaction cannot occur without spectator ions as the charge of the system would not balance.

5. “What three things can be done to increase the rate of at which a substance is dissolved?” Three things that can be done to increase the rate at which a substance dissolves are: 1.increasing the surface area of the solute 2.stirring 3.heating the solution

6. “Are weak acids inherently safer than strong acids” No. The strength of an acid plays no role in determining its concentration which is a major factor in how harmful an acid is. Additionally weak acids maybe very toxic even at low concentrations (HF). We need to consider multiple factors to determine the safety of any compound.

7. “Name two types of reactions acids may undergo” Acids may undergo neutralization reactions when they react with a base. Acids may undergo oxidation-reduction reactions when they react with a metal.

8. “What could be done experimentally to determine whether a solution contains a buffer” Buffers resist changes in pH when small amounts of acid or base are added to them. To determine if a solution contains a buffer we could add small amounts of acid and base and measure how the pH changes. We could compare this to what happens when we add the same amounts of acid and base to pure water. If the pH of our sample remains relatively stable compared to water then it probably contains a buffer.

9. “Identify each of the following as either an electrolyte or non- electrolyte: (a) NH 4 C 2 H 3 O 2 (b) CH 3 OH (c) HCl (d) CO 2 ” (a) electrolyte (b) non-electrolyte (c) electrolyte (d) non-electrolyte

10. “What type of interaction forces may exist in a polar solvent?” Several interaction forces may exist in a polar solvent. This include Van Der Waals or dispersion forces, dipole-dipole forces, dipole-induced dipole forces and depending on the composition of the solvent H bonding.

11. “Place the following in order of their decreasing vapor pressure of water: (a) 0.1 M (NH 4 ) 2 SO 4 (b) 0.2 M CuSO 4 (c) 0.15 M KI” (c) = (a) < (b)

12. “What is diffusion?” Diffusion is the process in which solute particles move by purely random motion from a region of high concentration to region of lower concentration within a solution.

13. “What is osmosis?” Osmosis is the movement of solvent molecules across a semi- permeable membrane. The solvent moves from a region of low solute concentration to a region of high solute concentration.

14. “What is osmotic pressure?” The osmotic pressure of a solution is the pressure required to prevent a net change in solvent volume across a semi- permeable membrane.

15. “What is meant when a system is said to be at equilibrium” When the rate of two oppossing processes is equal so that there is no change in system the system is said to be at equilibrium. An example of a system at equilibrium, unfortunately the equilibrium position isn’t quite where desired.

16. “What is the vapor pressure of a liquid?” The vapor pressure of a liquid is the pressure is the pressure exerted by the vapor molecules.