pH

Topics 9 & 18Acids and Bases: 

Topics 9 & 18 Acids and Bases Ionization of Water The pH Scale

Ionization of Water: 

Ionization of Water Occasionally, in water, a H+ is transferred between H2O molecules . . . . . . . . H:O: + :O:H H:O:H + + :O:H- . . . . . . . . H H H water molecules hydroxonium hydroxide ion (+) ion (-)

Pure Water is Neutral: 

Pure Water is Neutral Pure water contains small, but equal amounts of ions: H3O+ and OH- H2O + H2O H3O+ + OH- hydroxonium hydroxide ion ion 1 x 10-7 M 1 x 10-7 M H3O+ OH-

Ion Product of Water Kw: 

Ion Product of Water Kw [ ] = Molar concentration Kw = [ H3O+ ] [ OH- ] = [ 1 x 10-7 ][ 1 x 10-7 ] = 1 x 10-14

Acids: 

Acids Increase H+ HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq) More [H3O+] than water > 1 x 10-7M As H3O+ increases, OH- decreases [H3O+] > [OH-] H3O+ OH-

Bases: 

Bases Increase the hydroxide ions (OH-) H2O NaOH (s) Na+(aq) + OH- (aq) More [OH-] than water, [OH-] > 1 x 10-7M When OH- increases, H3O+ decreases [OH] > [H3O+] H3O+ OH-

Using Kw: 

Using Kw The [OH- ] of a solution is 1.0 x 10- 3 M. What is the [H3O+]? Kw = [H3O+ ] [OH- ] = 1.0 x 10-14 [H3O+] = 1.0 x 10-14 [OH-] [H3O+] = 1.0 x 10-14 = 1.0 x 10-11 M 1.0 x 10- 3

Learning Check pH1: 

Learning Check pH1 The [H3O+] of lemon juice is 1.0 x 10-3 M. What is the [OH-] of the solution? 1) 1.0 x 103 M 2) 1.0 x 10-11 M 3) 1.0 x 1011 M

Solution pH1: 

Solution pH1 The [H3O+] of lemon juice is 1.0 x 10- 3 M. What is the [OH-]? [OH- ] = 1.0 x 10 -14 = 1.0 x 10-11 M 1.0 x 10 - 3

Using the Calculator: 

Using the Calculator 1.0 x 10 -14 4.0 x 10-5 Enter 1.0 EE +/- 14  4.0 EE +/- 5 = 2.5 x 10 -10

Learning Check pH2: 

Learning Check pH2 The [OH-] of a solution is 5 x 10 -5 M. What is the [H3O+ ] of the solution? 1) 2 x 10- 5 M 2) 1 x 1010 M 3) 2 x 10-10 M

Solution pH2: 

Solution pH2 The [OH-] of a water solution is 5 x 10-5 M. What is the [H3O+] in the solution? [ H3O+] = 1.0 x 10 -14 5 x 10- 5 On some calculators: 1.0 EE +/- 14  5 EE +/- 5 = 2 x 10 -10 M

Learning Check pH3: 

Learning Check pH3 A.The [OH-] when [H3O+ ] of 1 x 10- 4 M 1) 1 x 10-6 M 2) 1 x 10-8 M 3) 1 x 10-10 M B.The [H3O+] when [OH- ] of 5 x 10-9 M 1) 1 x 10- 6 M 2) 2 x 10- 6 M 3) 2 x 10-7 M

Solution pH3: 

Solution pH3 Kw = [H3O+ ][OH-] = 1.0 x 10 14 A. (3) [OH- ] = 1.0 x 10 -14 = 1.0 x 10 -10 1.0 x 10- 4 B. (2) [H3O+] = 1.0 x 10 -14 = 2 x 10 - 6 5 x 10- 9

pH: 

pH Indicates the acidity [H3O+] of the solution pH = - log [H3O+] From the French pouvoir hydrogene (“hydrogen power” or power of hydrogen)

pH: 

In the expression for [H3O+] 1 x 10-exponent the exponent = pH [H3O+] = 1 x 10-pH M pH

pH Range: 

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

Some [H3O+] and pH: 

Some [H3O+] and pH [H3O+] pH 1 x 10-5 M 5 1 x 10-9 M 9 1 x 10-11 M 11

pH of Some Common Acids: 

pH of Some Common Acids gastric juice 1.0 lemon juice 2.3 vinegar 2.8 orange juice 3.5 coffee 5.0 milk 6.6

pH of Some Common Bases: 

pH of Some Common Bases blood 7.4 tears 7.4 seawater 8.4 milk of magnesia 10.6 household ammonia 11.0

Learning Check pH4 : 

Learning Check pH4 A. The [H3O+] of tomato juice is 1 x 10-4 M. What is the pH of the solution? 1) - 4 2) 4 3) 8 B. The [OH-] of an ammonia solution is 1 x 10-3 M. What is the pH of the solution? 1) 3 2) 11 3) -11

Solution pH4: 

Solution pH4 A. pH = - log [ 1 x 10-4] = -(- 4) = 4 B. [H3O+] = 1 x 10-11 pH = - log [ 1 x 10- 11] = -(- 11) = 11

Learning Check pH5: 

Learning Check pH5 The pH of a soap is 10. What is the [H3O+] of the soap solution? 1) 1 x 10 - 4 M 2) 1 x 1010 M 3) 1 x 10 - 10 M

Solution pH5: 

Solution pH5 The pH of a soap is 10. What is the [H3O+] of the soap solution? [H3O+] = 1 x 10-pH M = 1 x 10-10 M

pH on the Calculator: 

pH on the Calculator [H3O+] is 4.5 x 10-6 M pH = 4.5 x EXP(or EE) 6+/- LOG +/- = 5.35

Learning Check pH6: 

Learning Check pH6 A soap solution has a [H3O+] = 2 x 10-8 M. What is the pH of the solution? 1) 8 2) 7.7 3) 6

Solution pH6: 

Solution pH6 A soap solution has a [H3O+] = 2.0 x 10-8 M. What is the pH of the solution? B) 2.0 EE 8 +/- LOG +/- = 7.7

Learning Check pH7: 

Learning Check pH7 Identify each solution as 1. acidic 2. basic 3. neutral A. _____ HCl with a pH = 1.5 B. _____ Pancreatic fluid [H+] = 1 x 10-8 M C. _____ Sprite soft drink pH = 3.0 D. _____ pH = 7.0 E. _____ [OH- ] = 3 x 10-10 M F. _____ [H+ ] = 5 x 10-12

Solution pH7: 

Solution pH7 Identify each solution as 1. acidic 2. basic 3. neutral A. _1__ HCl with a pH = 1.5 B. _2__ Pancreatic fluid [H+] = 1 x 10-8 M C. _1__ Sprite soft drink pH = 3.0 D. _3__ pH = 7.0 E. _1__ [OH-] = 3 x 10-10 M F. _2__ [H+] = 5 x 10-12

Acid Rain: 

Acid Rain Unpolluted rain has a pH of 5.6 Rain with a pH below 5.6 is “acid rain“ CO2 in the air forms carbonic acid CO2 + H2O H2CO3 Adds to H+ of rain H2CO3 H+ (aq) + HCO3-(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 N2 SO2 26 million tons in 1980 NO and NO2 22 million tons in 1980 Mt. St Helens (1980) 400,000 tons SO2 2. Reactions in the atmosphere form SO3 2SO2 + O2  2 SO3 3. Reactions with atmosphere water form acids SO3 + H2O  H2SO4 sulfuric acid NO + H2O  HNO2 nitrous acid HNO2 + H2O  HNO3 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

Sources of Acid Rain: 

Sources of Acid Rain Power stations Oil refineries Coal with high S content Car and truck emissions Bacterial decomposition, and lighting hitting N2

Slide32: 

SO2 26 million tons in 1980 NO and NO2 22 million tons in 1980 Mt. St Helens (1980) 400,000 tons SO2 Reactions with oxygen in air form SO3 2SO2 + O2 2 SO3 Reactions with water in air form acids SO3 + H2O H2SO4 sulphuric acid NO + H2O HNO2 nitrous acid HNO2 + H2O HNO3 nitric acid

Effects of Acid Rain: 

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