1. Unit 4 Acids, Bases and pH

2. Water molecules dissociate and ionize to form H 2 0  H + + OH - Water  hydrogen ion + hydroxide ion In pure water, there is a small but equal concentration of hydrogen ions and hydroxide ions.

3. The concentrations of H+ and OH- in pure water are equal. The actual concentrations are –10 -7 moles/Liter A solution with this concentration is said to be neutral.

4. Acid –A substance that releases H+ when dissolved in water. Base –A substance that reduces the H+ concentration –Donates hydroxide ions to interact with hydrogen ions to form water, OR –Directly accept hydrogen ions to from another molecule.

5. pH pH is the measure of the hydrogen ion concentration in a solution. pH is the negative log of the hydrogen ion concentration –Hydrogen ion concentration of 10 -7, pH 7 –Hydrogen ion concentration of 10 -2, pH 2 –Hydrogen ion concentration of 10 -9, pH 9 pH below 7, acidic pH above 7, basic

6. pH Indicators Plant pigments –Change color in response to pH –Made from boiled red cabbage Make a set of standards using known pH buffers –Add 5 ml of pH buffer, then 3 ml cabbage juice to each tube. –Record color Compare your unknowns to your standard to determine pH of unknown. Exercise 4.1 and 4.2

7. Using pH meter and pH paper We are using red hand-held meters, NOT the Pasco probes Calibrate pH meter using the small screwdriver on cart. Follow directions at your table. Test pH of several household substances with both the meter and the paper Exercise 4.3

8. Buffering capacity of a solution Buffer- a substance in a solution that resists dramatic changes in pH. Buffering capacity- extent to which a solution can resist changes in pH

9. Acid- Hydrochloric acid (HCl) Base- Sodium hydroxide (NaOH)

10. Exercise 4.4 Solution A –Test buffering capacity of solution A by adding acid to the solution (1 mL at at time) and testing the pH. –Then test Solution A by adding a base (1 ml at a time.) Solution B –Add acid to the solution and test pH –Add base to the solution and test pH

11. Graph your results. Which is the better buffer, A or B?