Neutralisation of acids and salt production

• • A base is a chemical that neutralises acids
• • Examples of bases include:
  • Metal oxides, e.g. copper(II) oxide, Cu2O
  • Metal hydroxides, e.g. sodium hydroxide, NaOH
  • Metal carbonates, e.g. calcium carbonate, CaCO3 
• • Many bases are insoluble in water
  • Some bases dissolve in water and are called alkalis because they form an alkaline solution
  • Examples of alkalis are soluble metal hydroxides such as sodium hydroxide, NaOH (aq), and calcium hydroxide, Ca(OH)2 (aq)
• • Bases have pH values above 7
• • In a acid and base neutralisation reactions, salt and water are produced:

  acid + base ⟶ salt + water

  • If the base is a metal carbonate, carbon dioxide is also produced:

  acid + base ⟶ salt + water + carbon dioxide
• • The identity of the salt produced depends on the acid used and the positive ions in the base
  • Hydrochloric acid produces chlorides
  • Sulfuric acid produces sulfate
  • Nitric acid produces nitrates

  
• • For a neutralisation reaction to occur, water must be formed.
  • Therefore, the reaction between an acid and a metal is not a neutralisation reaction.
  • If an acid-base reaction effervesces (fizzes), then the base must be a metal carbonate as carbon dioxide gas is produced.
• • Metal carbonates act as base when reacting with acids in a neutralisation reaction to form the metal salt, carbon dioxide and water
  • These reactions are easily distinguishable from acid and metal oxide/hydroxide reactions due to the effervescence (fizzing) caused by the release of carbon dioxide gas
  • We can test for the presence of carbon dioxide gas by bubbling it through limewater
  • If the limewater turns milky or cloudy carbon dioxide is present
• • The name of a salt has two parts
  • The first part comes from the metal used in the reaction
  • The second part comes from the acid

  
• • Hydrochloric acid always produces salts that end in chloride and contain the chloride ion, Cl–
  • Sulfuric acid always produces salts that end in chloride and contain the sulfate ion, SO42–
  • Nitric acid always produces salts that end in chloride and contain the nitrate ion, NO3–
• • Salts have no overall charge since the sum of the charges on the ions is equal to zero
  • If you know the ions present in a salt you can identify the formula from balancing the charges

  
• the three common acids are:

  • hydrochloric acid -HCl
  • nitric acid -HNO3
  • sulfuric acid -H2SO4