1. Chapter 20 pH

2. Water forms ions H 2 O ----> H + + OH - Water splits apart into hydrogen ions (H+) and hydroxide ions (OH-). This process is called self-ionization.

3. pH pH stands for potential hydrogen. It is a measure of the hydrogen ion (H+) concentration in a solution.

4. Acids An acid is a substance that increases the Hydrogen ion (H+) concentration in a solution. Acids taste sour. Common acids include:  Battery acid  Stomach acid  Lemon juice, tomatoes  Vinegar  Beer, wine, soda, coffee  Rain  Milk  Urine Acids used in Chemistry HCl Hydrochloric acid HNO 3 Nitric acid H 2 SO 4 Sulfuric acid H 3 PO 4 Phosphoric acid CH 3 COOH Ethanoic acid H 2 CO 3 Carbonic acid

5. Bases A base is a substance that reduces the the H+ concentration in a solution. It has a lot of OH- ions. Bases taste bitter and feel slippery. Common bases include:  Blood  Seawater  Pepto Bismal, Tums, etc.  Soap  Ammonia  Bleach  Oven Cleaner Bases used in Chemistry KOH Potassium hydroxide NaOH Sodium hydroxide Ca(OH) 2 Calcium hydroxide Mg(OH) 2 Magnesium hydroxide

6. Neutral pH If the concentration of hydrogen ions and hydroxide ions is equal, a solution is said to have a neutral pH. Pure water (distilled water) has a neutral pH

7. pH Scale The pH scale ranges from 0-14. Acids are less than 7, Bases are greater than 7.

8. Determining pH from H+ concentration The numbers on the scale come from the H+ ion concentration, for example: [H + ] = 10 -7  pH = 7 [H + ] = 10 -4  pH = 4 [H + ] = 10 -12  pH = 12 pH values are equal to the absolute value of the exponent of the H+ ion concentration.

9. Determining pH from OH- concentration The pH is the absolute value of 14 minus the absolute value of the [OH - ] concentration [OH - ] = 10 -10  pH= 4 [OH - ] = 10 -3  pH= 11 [OH - ] = 10 -2  pH= 12

10. pH scale Most biological fluids have pH 6 – 8  pH values in human stomach can reach 2 Each pH unit represents a 10-fold difference in H + & OH - concentrations.  small change in pH actually indicates a substantial change in [H + ] & [OH - ]

11. Buffers Buffers are substances that minimize changes in the concentrations of H+ and OH- in solution. Buffers in your blood keep your pH close to 7.4 by accepting or donating H+ ions as needed.

12. Determining pH Titration: you add an indicator and watch for a color change pH meter: electronic, very sensitive pH paper (Litmus paper): color change scale Cabbage Juice: natural pH indicator, color change

13. pH Lab Use the garbage cans!! Do the front side BEFORE you start your lab. You will be testing 10 substances:  1. isopropyl alcohol  2. vinegar  3. baking soda solution  4. 7-up soda  5. hydrogen peroxide  6. alka seltzer solution  7. pineapple juice  8. bottled water  9. tap water (get some from the faucet)  10. your spit