Acid – Base Reactions

Definition of a Base

  • Bases have pH values above 7.
  • Many bases are insoluble in water but the ones that do dissolve in water are called alkalis.
  • They thus form an alkaline solution.
  • Examples of alkalis are soluble metal hydroxides such as NaOH and Ca(OH)2.
  • When they react with acid, a neutralisation reaction occurs.
  • In all acid-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 salts and nitric acid produces nitrates.

Reactions of Acids with Metal Oxides and Metal Hydroxides

  • Metal oxides and metal hydroxides act as bases.
  • When they react with acid, a neutralisation reaction occurs.
  • In all acid-base neutralisation reactions, salt and water are produced.

General equations

Acid Base General Equation Table, IGCSE & GCSE Chemistry revision notes

  • The following are common reactions between acids and metal oxides / hydroxides:

2HCl + CuO ⟶ CuCl2 + H2O

H2SO4 + 2NaOH ⟶ Na2SO4 + 2H2O

HNO3 + KOH ⟶ KNO3 + H2O

Reactions of Acids with Metal Carbonates

  • Acids will react with metal carbonates to form the corresponding metal salt, carbon dioxide and water.
  • These reactions are easily distinguishable from acid – metal oxide/hydroxide reactions due to the presence of effervescence caused by the carbon dioxide gas.

General equations

Reactions of Acids with Metal Carbonates Table, IGCSE & GCSE Chemistry revision notes

  • The following are common reactions between acids and metal carbonates:

2HCl + NaCO3 ⟶ 2NaCl + H2O + CO2

H2SO4 + CaCO3⟶ CaSO4 + H2O + CO2

Formulae of Common Salts & Ions

Salts

  • A salt is a compound that is formed when the hydrogen atom in an acid is replaced by a metal.
  • For example if we replace the H in HCl with a potassium atom, then the salt potassium chloride is formed, KCl.
  • Salts are an important branch of chemistry due to the varied and important uses of this class of compounds.
    These uses include fertilisers, batteries, cleaning products, healthcare products and fungicides.

Naming salts

  • The name of a salt has two parts.
  • The first part comes from the metal, metal oxide or metal carbonate used in the reaction.
  • The second part comes from the acid.
  • The name of the salt can be determined by looking at the reactants
  • For example hydrochloric acid always produces salts that end in chloride and contain the chloride ion, Cl.
  • Other examples:
    • Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride.
    • Zinc oxide reacts with sulfuric acid to produce zinc sulfate.
  • A list of the common ions and their formulae is shown below.

Naming salts table, IGCSE & GCSE Chemistry revision notes

  • Salts have no overall charge since the sum of the charges on the ions is equal to zero.
  • From the table of the common ions it’s clear the charges on each the Group I elements is always +1, Group II is +2, Group VI is -2 and Group VII is -1.
  • If you know the ions present in a salt you can identify the formula from balancing the charges.
  • Example: what is the formula of magnesium phosphate?
    • Write out the formulae of each ion, including their charges.
    • Mg2+ PO43-
  • Balance the charges by multiplying them out: Mg2+ x 3 = +6 and PO43- x 2 = -6; so +6 – 6 = 0.
  • So the formula is Mg3(PO4)2.

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.