The pH Scale

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pH

Indicates the acidity [H3O+] of the solution

pH = - log [H3O+]

From the French pouvoir hydrogene (“hydrogen power” or power of hydrogen)

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In the expression for [H3O+]

1 x 10-exponent

the exponent = pH

[H3O+] = 1 x 10-pH M

pH

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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

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Some [H3O+] and pH

[H3O+] pH

1 x 10-5 M 5

1 x 10-9 M 9

1 x 10-11 M 11

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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

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pH of Some Common Bases

blood 7.4

tears 7.4

seawater 8.4

milk of magnesia 10.6

household ammonia 11.0

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pH on the Calculator

[H3O+] is 4.5 x 10-6 M

pH = 4.5 x EXP(or EE) 6+/- LOG +/-

= 5.35

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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 acidsSO3 + H2O H2SO4 sulfuric acid

NO + H2O HNO2 nitrous acid

HNO2 + H2O HNO3 nitric acid

4. Effects of Acid RainDecline in fish populations in rivers and lasts due to toxic effect of Al leached from soil by acid rainExtensive 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 bacteriaCorrodes metals, textiles, paper and leather

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Sources of Acid Rain

Power stationsOil refineries

Coal with high S content

Car and truck emissions

Bacterial decomposition, and lighting hitting N2

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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 sulfuric acid

NO + H2O HNO2 nitrous acid

HNO2 + H2O HNO3 nitric acid

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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