Chapter 9Acids and Bases Ionization of Water The pH Scale

Ionization of Water Occasionally, in water, a H + is transferred between H 2 O molecules H : O : + : O : H H : O : H + + : O : H H H H water molecules hydronium hydroxide ion (+) ion (-)

Pure Water is Neutral Pure water contains small, but equal amounts of ions: H 3 O + and OH - H 2 O + H 2 O H 3 O + + OH - hydronium hydroxide ion ion 1 x M H3O+H3O+ OH -

Ion Product of Water K w [ ] = Molar concentration K w = [ H 3 O + ] [ OH - ] = [ 1 x ][ 1 x ] = 1 x

Acids Increase H + HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) More [H 3 O + ] than water > 1 x M As H 3 O + increases, OH - decreases [H 3 O + ] > [OH - ] H3O+H3O+ OH -

Bases Increase the hydroxide ions (OH - ) H 2 O NaOH (s) Na + (aq) + OH - (aq) More [OH - ] than water, [OH - ] > 1 x M When OH - increases, H 3 O + decreases [OH  ] > [H 3 O + ] H3O+H3O+ OH -

Using K w The [OH - ] of a solution is 1.0 x M. What is the [H 3 O + ]? K w = [H 3 O + ] [OH - ]= 1.0 x [H 3 O + ] =1.0 x [OH - ] [H 3 O + ] = 1.0 x = 1.0 x M 1.0 x

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)

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

Some [H 3 O + ] and pH [H 3 O + ] pH 1 x M 5 1 x M 9 1 x M 11

pH Range Neutral [H + ] > [OH - ] [H + ] = [OH - ] [OH - ] > [H + ] Acidic Basic

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

Solution pH1 The [H 3 O + ] of lemon juice is 1.0 x M. What is the [OH - ]? [OH - ] = 1.0 x = 1.0 x M 1.0 x

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

Solution pH2 The [OH - ] of a water solution is 5 x M. What is the [H 3 O + ] in the solution? [ H 3 O + ] = 1.0 x x On some calculators: 1.0 EE +/- 14  5 EE +/- 5 = 2 x M

Learning Check 3 A.The [OH - ] when [H 3 O + ] of 1 x M 1) 1 x M 2) 1 x M 3) 1 x M B.The [H 3 O + ] when [OH - ] of 5 x M 1) 1 x M 2) 2 x M 3) 2 x M

Solution 3 K w = [H 3 O + ][OH - ] = 1.0 x A. (3) [OH - ] = 1.0 x = 1.0 x x B. (2) [H 3 O + ] = 1.0 x = 2 x x

Learning Check 3.1 In a M solution of HCl, what is the [ OH - ] in the solution? 1) 8.0 x M 2) 1.0 x M 3) 1.25 x M

Solution 3.1 In a M solution of HCl, what is the [ OH - ] in the solution? (A) HCl is a strong acid so it dissociates completely: M HCl = M H 3 O + [ H 3 O + ] = M H 3 O + [OH - ] = 1.0 x = 8.0 x M

Learning Check 4 A. The [H 3 O + ] of tomato juice is 1 x M. What is the pH of the solution? 1) - 42)43)8 B. The [OH - ] of an ammonia solution is 1 x M. What is the pH of the solution? 1) 32)113)-11

Solution 4 A. pH = - log [ 1 x ] = -(- 4) = 4 B. [H 3 O + ] = 1 x pH = - log [ 1 x ] = -(- 11) = 11

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

Solution pH5 The pH of a soap is 10. What is the [H 3 O + ] of the soap solution? [H 3 O + ] = 1 x 10 -pH M = 1 x M

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

Solution pH6 A soap solution has a [H 3 O + ] = 2.0 x M. What is the pH of the solution? B) 2.0 EE 8 +/- LOG +/- = 7.7

Learning Check pH7 Identify each solution as 1. acidic 2. basic3. neutral A. _____ HCl with a pH = 1.5 B. _____ Pancreatic fluid [H + ] = 1 x M C. _____ Sprite soft drink pH = 3.0 D. _____ pH = 7.0 E. _____ [OH - ] = 3 x M F. _____ [H + ] = 5 x

Solution pH7 Identify each solution as 1. acidic 2. basic3. neutral A. _1__ HCl with a pH = 1.5 B. _2__ Pancreatic fluid [H + ] = 1 x M C. _1__ Sprite soft drink pH = 3.0 D. _3__ pH = 7.0 E. _1__ [OH - ] = 3 x M F. _2__ [H + ] = 5 x

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

Sources of Acid Rain Power stations Oil refineries Coal with high S content Car and truck emissions 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 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

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

Practice Problem 1 What is the hydroxide ion concentration in an aqueous solution that has a concentration of hydronium ions equal to 1.55 x ?

Solution 1 What is the hydroxide ion concentration in an aqueous solution that has a concentration of hydronium ions equal to 1.55 x M? [ H 3 O + ] = 1.55 x [OH - ] = K w [ H 3 O + ] [OH - ] = 1.0 x = 6.45 x M 1.55 x 10 -2

Practice Problem 2 In a M solution of HCl, what is the [ OH - ] in the solution?

Solution 2 In a M solution of HCl, what is the [ OH - ] in the solution? ***HCl is a strong acid so it dissociates completely: M HCl = M H 3 O + [ H 3 O + ] = M H 3 O + [ OH - ] = K w [ H 3 O + ] [OH - ] = 1.0 x = 8.0 x M

Practice Problem 3 Calculate pH if the hyronium concentration is 3.5 x ?

Solution 3 Calculate pH if the hyronium concentration is 3.5 x ? [ H 3 O + ] = 3.5 x pH = -log [ H 3 O + ] pH = -log [ 3.5 x ] pH = 3.5

Practice Problem 4 Calculate pH of a solution with 0.15 moles per liter of HCl (strong)?

Solution 4 Calculate pH of a solution with 0.15 moles per liter of HCl (strong)? [ H 3 O + ] =.15 M pH = -log [ H 3 O + ] pH = -log [.15 ] pH =.82

Practice Problem 5 Calculate the hydronium concentration of lemon juice which has a pH of 2.25.

Solution 5 Calculate the hydronium concentration of lemon juice which has a pH of [ H 3 O + ] = 1.0 x 10 -ph [ H 3 O + ] = 1.0 x [ H 3 O + ] = 5.6 x 10 -3

Practice Problem 6 Determine the concentrations of hydronium ions and hydroxide ion in milk of magnesia, which has a pH of 10.65

Solution 6 Determine the concentrations of hydromium ions and hydroxide ion in milk of magnesia, which has a pH of [ H 3 O + ] = 1.0 x 10 -ph [ H 3 O + ] = 1.0 x [ H 3 O + ] = 2.24 x M [OH - ] = 1.0 x = 4.46 x x M