6.3.1

Strong Acids & Bases

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Strong vs Weak Bases

Bases are metallic oxides or hydroxides (or ammonia) that neutralize acids to form salt and water. An alkali is a soluble base - one that dissolves in water.

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Strong base

  • Group I hydroxides, such as aqueous sodium hydroxide and potassium hydroxide are examples of strong bases.
  • Strong bases fully ionize in aqueous solutions.
    • NaOH(aq) → Na+(aq) + OH-.
    • KOH(aq) → K+(aq) + OH-.
  • As strong bases fully ionize, the initial concentration of a strong base equals the concentration of OH- ions.
    • For example, 1M KOH gives 1M OH- ions.
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Group II hydroxides

  • Group II hydroxides are also strong bases. An example is Ca(OH)2.
  • Due to stoichiometry, 1M of a group II hydroxide gives 2M OH- ions.
    • For example, 1M Ca(OH)2 gives 2M OH- ions.
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Weak base

  • Weak bases don't fully ionize in aqueous solutions.
  • Ammonia solution is an example of a weak base.
  • It exists mainly as NH3 molecules. Only a few of these react with water molecules to form ions.
    • NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq).

Strong vs Weak Acids

Acids are proton donors that neutralize bases to form salt and water. An acid can be strong or weak - this will affect its dissociation.

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Strong acid

  • Aqueous HCl, HBr, HI, HClO4, HNO3 and H2SO4 are examples of strong acids.
  • Strong acids fully ionize in aqueous solutions.
    • HCl(aq) + H2O(l) → H3O+(aq) + Cl-
    • HNO3(aq) + H2O(l) → H3O+(aq) + NO3-
  • As strong acids fully ionize, the initial concentration of a monoprotic strong acid equals the concentration of H3O+ ions.
    • For example, 1M HCl gives 1M H3O+ ions.
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Diprotic acids

  • Diprotic strong acids ionize to give two hydronium ions in solution. An example is H2SO4.
  • Due to stoichiometry, 1M of a diprotic acid gives 2M H3O+ ions.
    • For example, 1M H2SO4 gives 2M H3O+ ions.
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Weak acids

  • Weak acids don't fully ionize in aqueous solutions.
  • Acetic acid is an example of a weak acid.
    • Acetic acid exists mainly as CH3COOH molecules. Only a few of these react with water molecules to form ions.
    • CH3COOH(aq) + H2O(l) ⇌ H3O+(aq) + CH3COO-(aq)

Jump to other topics

1Structure - Models of the Particulate of Matter

2Structure - Models of Bonding & Structure

3Structure - Classification of Matter

3.1The Periodic Table: Classification of Elements

3.2Periodic Trends

3.3Group 1 Alkali Metals

3.4Halogens

3.5Noble gases, group 18

3.6Functional Groups: Classification of Organic

3.7Functional Group Chemistry

3.8Alkanes

3.9Alcohols

3.10Halogenoalkanes

4Reactivity - What Drives Chemical Reaction?

5Reactivity - How Much, How Fast & How Far?

6Reactivity - The Mechanisms of Chemical Change

7Measurement, Data Processing & Analysis

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