Topic 8: Acids and Bases

8.1 Theories of Acids and Bases

Arrhenius's theory of acid and base

  • Definition of acid: substance that when ionized in water produces 

  • Definition of base: substance that when ionized in water produces

Brønsted-Lowry acids and bases

  • Definition of acid: substance that donates protons

  • Definition of base: substance that accepts protons

Note: do not confuse with Lewis acid and bases!!!

  • conjugate acid acid-base pair:

    • species that differ by a single proton​

    • ​example​:

Amphiprotic species

  • Definition: species that may donate or accept protons

  • example:

Note: do not confuse with amphoteric

8.2 Properties of Acids and Bases

Proprieties of acids

  • sour taste

  • pH<7.0

  • litmus is red

  • phenolphthalein is colourless

  • methyl orange is red

Proprieties of bases

  • bitter taste 

  • ph>7.0

  • litmus is blue

  • phenolphthalein is pink

  • methyl orange is yellow

Reactions

  • acid + metal --> salt + hydrogen

  • Example:

  • acid + base --> salt + water

  • Example:

  • acid + metal carbonate/ hydrogen carbonate --> salt + carbon dioxide 

  • 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

  • An effective proton donor, that is assumed to completely dissociate in water.

  • There is no equilibrium.

  • Weak conjugate base.

  • Example:

Weak acid

  • A poor proton donor, dissociates only partially in water.

  • There is equilibrium.

  • Example:

Strong base

  • An effective proton acceptor, that is assumed to completely dissociate in water.

  • There is no equilibrium.

  • Weak conjugate acid.

  • Example:

Weak base

  • A poor proton acceptor, dissociate only partially in water.

  • There is equilibrium.

  • Example:

Conductivity: is proportional to the concentration of ions in the solution.

  • Strong acids and bases are good conductors

  • Weak acids and bases are bad conductors

Energy changes in neutralization

  • The weaker the acid the lower enthalpy change of neutralization

8.5 Acid Deposition

Acid deposition

  • Formation of pollutants that are deposited on Earth's surface, from acids

Acid rain

  • Due to         in the atmosphere

  • Reaction pathways:

  • pH< 5.6 (normal pH of rain)

Major pollutants (both cause acid rain)

  • Nitrogen Oxides

    • Reaction pathways:

  • Sulphur dioxide

    • Reaction pathways:

Pre combustion methods

  • physical cleaning

  • mineral beneficiation

    • example: crushing and then floating the coal before burning to remoce sulphur 

  • Removal of up to 80%-90% of impurities ​

Post combustion methods

  • Removal of gases before releasing in the atmosphere

    • example: car catalysts​

Effects of acid rain

  • Damage in limestone or marble buildings due to exposure to acid rain, as shown in the following reaction​​

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