Topic 8: Acids and Bases
8.1 Theories of Acids and Bases
Arrhenius's theory of acid and base
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Definition of acid: substance that when ionized in water produces
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Definition of base: substance that when ionized in water produces
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Brønsted-Lowry acids and bases
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Definition of acid: substance that donates protons
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Definition of base: substance that accepts protons
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Note: do not confuse with Lewis acid and bases!!!
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conjugate acid acid-base pair:
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species that differ by a single proton​
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​example​:
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Amphiprotic species
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Definition: species that may donate or accept protons
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example:
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Note: do not confuse with amphoteric


8.2 Properties of Acids and Bases
Proprieties of acids​
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sour taste
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pH<7.0
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litmus is red
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phenolphthalein is colourless
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methyl orange is red
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Proprieties of bases
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bitter taste
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ph>7.0
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litmus is blue
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phenolphthalein is pink
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methyl orange is yellow
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Reactions
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acid + metal --> salt + hydrogen
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Example:

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acid + base --> salt + water
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Example:

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​acid + metal carbonate/ hydrogen carbonate --> salt + carbon dioxide
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Example:

8.3 The pH Scale
Used to measure the concentration of hydrogen ions H+ in a solution





​Ionization of Water
8.4 Strong and Weak Acids and Bases
Strong acid
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An effective proton donor, that is assumed to completely dissociate in water.
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There is no equilibrium.
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Weak conjugate base.
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Example:

Weak acid
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A poor proton donor, dissociates only partially in water.
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There is equilibrium.
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Example:

Strong base
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An effective proton acceptor, that is assumed to completely dissociate in water.
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There is no equilibrium.
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Weak conjugate acid.
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Example:

Weak base
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A poor proton acceptor, dissociate only partially in water.
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There is equilibrium.
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Example:

Conductivity: is proportional to the concentration of ions in the solution.
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Strong acids and bases are good conductors
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Weak acids and bases are bad conductors
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Energy changes in neutralization
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The weaker the acid the lower enthalpy change of neutralization
8.5 Acid Deposition
Acid deposition
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Formation of pollutants that are deposited on Earth's surface, from acids
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Acid rain
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Due to in the atmosphere
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Reaction pathways:




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pH< 5.6 (normal pH of rain)
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Major pollutants (both cause acid rain)
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Nitrogen Oxides
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Reaction pathways:​
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Sulphur dioxide
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Reaction pathways:​
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​Pre combustion methods
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physical cleaning
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mineral beneficiation
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example: crushing and then floating the coal before burning to remoce sulphur
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Removal of up to 80%-90% of impurities ​
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Post combustion methods
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Removal of gases before releasing in the atmosphere
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example: car catalysts​
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Effects of acid rain
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Damage in limestone or marble buildings due to exposure to acid rain, as shown in the following reaction​​

