Reactions of acids

• Acids


  Compounds that, when dissolved in water, release H+ ions
• Main acids


  • Sulfuric acid H2SO4
  • Nitric acid HNO3
  • Hydrochloric acid HCl
• Alkalis


  Compounds that, when dissolved in water, release OH- ions
• pH scale


  Measure of acidity and alkalinity, runs from 1 to 14
• Aqueous solutions


  • pH < 7 are acidic
  • pH > 7 are alkaline
  • pH = 7 are neutral
• Logarithmic scale


  An increase of 1 on the pH scale is equal to a decrease of 10x the number of H+ ions in solution
• Acid with pH 3


  • 100x fewer H+ ions in solution than an acid with pH 1
  • 10x fewer H+ ions than pH 2
  • 10x more H+ ions than pH 4
  • 100x more H+ ions than pH 5
• Indicators


  Can show if something is an acid or an alkali
• Universal indicator


  • Can tell us the approximate pH of a solution
• Electronic pH probes


  Can give us the exact pH of a solution
• Indicators


  Can show if something is an acid or an alkali
• Universal indicator


  Can also tell us the approximate pH of a solution
• Electronic pH probes


  Can give us the exact pH of a solution
• Strong acids

  Sulfuric acid, nitric acid, and hydrochloric acid - they are completely ionised when dissolved in water
• Ionisation of strong acids

  1. H2SO4(aq) → 2H(aq) + SO4^2-(aq)

  2. HNO3(aq) → H(aq) + NO3-(aq)

  3. HCl(aq) → H(aq) + Cl-(aq)
• Weak acids

  Ethanoic acid, citric acid, and carbonic acid - they are partially ionised when dissolved in water
• Concentration of an acid

  The stronger the acid, the lower the pH
• Concentrated acids


  • Have lots of acid in a small volume of water
• Dilute acids


  • Have little acid in a large volume of water
• Acids react with metals or metal compounds to form salts
• A salt is a compound where the hydrogen from an acid has been replaced by a metal
• Salts formed from acids

  • Metal chloride
  • Metal sulfate
  • Metal nitrate
• Acids react with metals to form salts and hydrogen gas
• Acids react with metal hydroxides to form salts and water
• Neutralisation reaction of acids and metal hydroxides

  H+(aq) + OH-(aq) → H2O(l)
• Acids react with metal oxides to form salts and water
• Acids react with metal carbonates to form salts, water, and carbon dioxide
• Redox reaction


  The reaction of acids with metals - the metal is oxidised and hydrogen is reduced
• Bases


  Neutralise acids to form water in neutralisation reactions
• Alkalis


  Some metal hydroxides that dissolve in water to form alkaline solutions
• Bases


  Some metal oxides and hydroxides that do not dissolve in water
• Acids


  Weak acids are ionised in water
• Neutralisation reactions


  Reactions of acids
• Reactions of acids with metals

  1. Acids react with some metals to form salts and hydrogen gas

  2. magnesium + hydrochloric acid-sodium chloride + hydrogen
• Reactions of acids with metal hydroxides

  1. Acids react with metal hydroxides to form salts and water

  2. hydrochloric acid + sodium hydroxide-sodium chloride + water
• Ionic equation for acid-metal hydroxide reaction

  H(aq) +OH(aq) → H₂O(1)
• Reactions of acids with metal oxides

  1. Acids react with metal oxides to form salts and water

  2. hydrochloric acid + sodium oxide-sodium chloride + water
• Reactions of acids with metal carbonates

  1. Acids react with metal carbonates to form a salt, water, and carbon dioxide

  2. hydrochloric acid + sodium carbonate sodium chloride + water + carbon dioxide
• Redox


  The reaction between an acid and a metal carbonate is a redox reaction
• Alkali


  Bases that dissolve in water