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ACIDS AND BASES

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Title: ACIDS AND BASES


1
ACIDS AND BASES
  • for it cannot be
  • But I am pigeon-liverd and lack gall
  • To make oppression bitter
  • Hamlet

2
Learning objectives
  • Describe properties of acids and bases
  • Define acid and base using Arrhenius and Bronsted
    definitions
  • Identify Bronsted acids and bases in solution
    equilibria
  • Distinguish between strength and concentration of
    acids and bases
  • Estimate pH of common substances
  • Describe phenomenon of acid rain

3
Properties of acids
  • Acids are sour
  • Acids attack metals
  • Acids react with bases and form salts
  • Acids turn litmus red

4
Properties of bases
  • Bases taste bitter
  • Bases are slippery
  • Bases react with acids to form salts
  • Bases turn litmus blue

5
Neutralization
  • The mixing of an acid with a base
  • ACID BASE SALT WATER
  • The reaction of carbonic acid (CO2 in H2O) to
    give limestone
  • H2CO3 Ca(OH)2 CaCO3 2H2O

6
Arrhenius its about water
  • The meaning of acid and base has changed over the
    years
  • Arrhenius acid is one that generates protons when
    dissolved in water
  • Arrhenius base is one that generates hydroxide
    ions when dissolved in water

7
Hydronium ion is the active ingredient of an acid
in water
  • Protons do not exist in solution
  • CH3CO2H H2O H3O CH3CO2-
  • Vinegar in water produces hydronium ions

8
Hydroxide ion is the active ingredient of a base
in water
  • NH3 H2O NH4 OH-
  • Ammonia, a base, dissolves in water and produces
    hydroxide ions

9
The essence of neutralization
  • Elimination of the components of acid and base by
    combination to give H2O
  • H OH- ? H2O

BASE
ACID
10
Brønsted and Lowry All about protons
  • Broader definition of acids and bases
  • Reaction NH3 HCl NH4Cl has all elements of
    acid-base neutralization but no H2O
  • Brønsted acid donates a proton
  • Brønsted base accepts a proton

11
Brønsted acid
  • HCl H2O H3O Cl-

12
Brønsted base
  • NH3 H2O NH4 OH-
  • water
  • NH3 HCl NH4Cl-
  • No water

13
Substances can be both acids and bases depends
on environment
  • Note that in one instance H2O behaves like a base
    accepting protons, and in another, behaves like
    an acid donating protons
  • HCl H2O H3O Cl-
  • In presence of an acid H2O is a base
  • NH3 H2O NH4 OH-
  • In presence of a base H2O is an acid

14
Salts
  • Products of acid-base neutralization
  • Contain metal cation and nonmetal anion
  • Acid base salt water
  • HCl NaOH NaCl H2O
  • HCl KOH KCl H2O
  • HNO3 KOH KNO3 H2O
  • 2HCl Ca(OH)2 CaCl2 2H2O
  • HCN NaOH NaCN H2O

15
Strong coffee (or concentrated?)
  • Not all acids completely donate protons to water
    molecules
  • HA H2O ? A- H3O
  • Strength Degree of ionization
  • Concentration Number of moles per unit volume

16
Strong and weak
  • Strong acid (HCl)
  • Fully ionized
  • All H and Cl-
  • Corrosive
  • Weak acid (Acetic)
  • Weakly ionized
  • Mostly CH3COOH
  • Edible

17
Changing concentration does not change strength
  • Strength refers to degree of ionization
  • Strong is completely ionized (100 )
  • Weak is partly ionized (1 - 1106)
  • Concentration refers to number of moles per unit
    volume
  • An acid (or base) can be strong and concentrated,
    weak and concentrated, strong and dilute, weak
    and dilute

18
Ionization of water
  • Even in pure water, molecules are ionized and
    concentrations of OH- and H3O are equal
  • H2O H2O H3O OH-
  • H3O OH-

Concentration
19
In all aqueous solutions, product of
concentrations is a constant
  • H3OOH- constant
  • Increasing H3O decreases OH-
  • (acidic conditions)
  • Increasing OH- decreases H3O
  • (basic conditions)

20
(No Transcript)
21
The pH scale reduces large range of numbers to
small
  • In water H3OOH- 10-14
  • pH - log10H3O
  • Range of H3O 10 M 10-14 M
  • Range of pH -1 to 14
  • Low pH acid high pH basic
  • pH 7 neutral

22
Relating pH to H3O
  • For pH, take exponent of H3O, change sign
  • 10-1 M (0.1 M) HCl has pH 1
  • Pure water has H3O 10-7 M, pH 7
  • Ammonia has H3O 10-11 M, pH 11
  • Note change of 1 unit in pH is factor of ten

23
Estimating pH
  • Estimating pH is often more useful than doing
    exact calculations
  • Smaller pH value means larger H concentration
  • Estimating pH

24
Acidity and the environment
  • Rain is naturally weakly acidic because of CO2
  • Alkaline rocks limestone neutralize the acid

25
Acid Rain
  • Acid rain is polluted by acid in the atmosphere.
    Two common pollutants acidify rain sulphur
    dioxide (SO2) and nitrogen oxides (NOX)
  • Following information from The Green LaneTM,
    Environment Canada's World Wide Web site -
    www.ec.gc.ca/regeng.html

26
Whats the big deal?
  • Damage to aquatic life
  • Damage to buildings
  • Damage to forests
  • Damage to air quality

27
Source of the problem
  • Sulphur dioxide (SO2) byproduct of industrial
    processes and burning fossil fuels.
  • Ore smelting
  • coal-fired power generators
  • natural gas processing

28
Where do NOX emissions come from?
  • Main source of NOX is combustion of fuels in
    motor vehicles, residential and commercial
    furnaces, industrial and electrical-utility
    boilers and engines.
  • NOX emissions were 2.5 million tonnes in 2000.
    U.S. NOX emissions for 2000 were 21 million
    tonnes.

29
Legislative success with acid rain
  • Eastern Canada Acid Rain program committed Canada
    to cap SO2 emissions at 2.3 million tonnes by
    1994 - 40 reduction from 1980 levels
  • Targets achieved or exceeded
  • By 2001, emissions were 63 reduction from 1980
    levels.

30
Would acid rain remain a problem without further
controls?
  • Yes. That is why The Canada-Wide Acid Rain
    Strategy for Post-2000 calls for further emission
    reductions in both Canada and the United States.
  • In total, without further controls, almost
    800,000 km2 in southeastern Canada-an area the
    size of France and the United Kingdom
    combined-would receive harmful levels of acid
    rain that is, levels well above critical load
    limits for aquatic systems.
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