1. 10.5-10.6 Ionization of Water and the pH Scale

2. Ionization of Water 10.5

3. 3 In water, H + is transferred from one H 2 O molecule to another. one water molecule acts as an acid, while another acts as a base. H 2 O + H 2 O H 3 O + + OH −........ :O: H + H:O: H:O:H + + :O:H −........ H H H water water hydronium hydroxide ion (+) ion (-) Ionization of Water

4. 4 Pure Water is Neutral In pure water, the ionization of water molecules produces small, but equal quantities of H 3 O + and OH − ions. molar concentrations are indicated in brackets as [H 3 O + ] and [OH − ]. [H 3 O + ] = 1.0 x 10 − 7 M [OH − ] = 1.0 x 10 − 7 M Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

5. 5 Acidic Solutions Adding an acid to pure water increases the [H 3 O + ]. cause the [H 3 O + ] to exceed 1.0 x 10 -7 M. decreases the [OH − ].

6. 6 Basic Solutions Adding a base to pure water increases the [OH − ]. causes the [OH − ] to exceed 1.0 x 10 − 7 M. decreases the [H 3 O + ]. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

7. 7 The ion product constant, K w, for water is the product of the concentrations of the hydronium and hydroxide ions. K w = [ H 3 O + ] [ OH − ] can be obtained from the concentrations in pure water. K w = [ H 3 O + ] [ OH − ] K w = [1.0 x 10 − 7 M] x [ 1.0 x 10 − 7 M] = 1.0 x 10 − 14 Ion Product of Water, K w

8. 8 [H 3 O + ] and [OH − ] in Solutions In neutral, acidic, or basic solutions, the K w is always 1.0 x 10 −14.

9. 9 Guide to Calculating [H 3 O + ]

10. 10 Calculating [H 3 O + ] What is the [H 3 O + ] of a solution if [OH − ] is 5.0 x 10 -8 M? STEP 1: Write the K w for water. K w = [H 3 O + ][OH − ] = 1.0 x 10 −14 STEP 2: Rearrange the K w expression. [H 3 O + ] = 1.0 x 10 -14 [OH − ] STEP 3: Substitute [OH − ]. [H 3 O + ] = 1.0 x 10 -14 = 2.0 x 10 -7 M 5.0 x 10 - 8

11. The pH Scale 10.6

12. LecturePLUS Timberlake12 pH Indicates the acidity [H 3 O + ] of the solution pH = - log [H 3 O + ] From the French pouvoir hydrogene ( “ hydrogen power ” or power of hydrogen)

13. LecturePLUS Timberlake13 In the expression for [H 3 O + ] 1 x 10 -exponent the exponent = pH [H 3 O + ] = 1 x 10 -pH M pH

14. LecturePLUS Timberlake14 pH Range 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Neutral [H + ] > [OH - ] [H + ] = [OH - ] [OH - ] > [H + ] Acidic Basic

15. LecturePLUS Timberlake15 Some [H 3 O + ] and pH [H 3 O + ] pH 1 x 10 -5 M 5 1 x 10 -9 M 9 1 x 10 -11 M 11

16. LecturePLUS Timberlake16 pH of Some Common Acids gastric juice1.0 lemon juice2.3 vinegar2.8 orange juice3.5 coffee5.0 milk6.6

17. LecturePLUS Timberlake17 pH of Some Common Bases blood 7.4 tears 7.4 seawater 8.4 milk of magnesia10.6 household ammonia11.0

18. LecturePLUS Timberlake18 pH on the Calculator [H 3 O + ] is 4.5 x 10 -6 M pH = 4.5 x EXP(or EE) 6+/- LOG +/- = 5.35

19. LecturePLUS Timberlake19 Acid Rain Unpolluted rain has a pH of 5.6 Rain with a pH below 5.6 is “ acid rain “ CO 2 in the air forms carbonic acid CO 2 + H 2 O H 2 CO 3 Adds to H + of rain H 2 CO 3 H + (aq) + HCO 3 -(aq) Formation of acid rain: 1. Emission of sulfur and nitrogen oxides from the burning of fuels expecially coal with high S content, power stations, oil refineries, vehicles as well as bacterial decomposition, and lighting hitting N 2 SO 2 26 million tons in 1980 NO and NO 2 22 million tons in 1980 Mt. St Helens (1980) 400,000 tons SO 2 2. Reactions in the atmosphere form SO 3 2SO 2 + O 2  2 SO 3 3. Reactions with atmosphere water form acids SO 3 + H 2 O  H 2 SO 4 sulfuric acid NO + H 2 O  HNO 2 nitrous acid HNO 2 + H 2 O  HNO 3 nitric acid 4. Effects of Acid Rain Decline in fish populations in rivers and lasts due to toxic effect of Al leached from soil by acid rain Extensive fish kills in spring from runoff due to accumulation of large amounts of acid on the snow Dissolves minerals Mg, Ca, and K from the soil and waxy coatings that protect leaves from bacteria Corrodes metals, textiles, paper and leather

20. LecturePLUS Timberlake20 Sources of Acid Rain Power stations Oil refineries Coal with high S content Car and truck emissions Bacterial decomposition, and lighting hitting N 2

21. LecturePLUS Timberlake21 SO 2 26 million tons in 1980 NO and NO 2 22 million tons in 1980 Mt. St Helens (1980) 400,000 tons SO 2 Reactions with oxygen in air form SO 3 2SO 2 + O 2 2 SO 3 Reactions with water in air form acids SO 3 + H 2 O H 2 SO 4 sulfuric acid NO + H 2 O HNO 2 nitrous acid HNO 2 + H 2 O HNO 3 nitric acid

22. LecturePLUS Timberlake22 Effects of Acid Rain Leaches Al from soil, which kills fish Fish kills in spring from runoff due to accumulation of large amounts of acid in snow Dissolves waxy coatings that protect leaves from bacteria Corrodes metals, textiles, paper and leather