AQA GCSE Chemistry

Revision Notes

4.2.3 Neutralisation of Acids and Salt Production

Acid - Base Reactions

  • When an acid reacts with a base, a neutralisation reaction occurs
  • 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
  • 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

Acids and Metals Oxides or Hydroxides Summary Table

Acids & Metal Oxides or Hydroxides Summary Table, downloadable IGCSE & GCSE Chemistry revision notes

  • The following are some specific examples of 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 saltcarbon 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

Acids & Metal Carbonates Reactions Table

Acid & Metal Carbonate Reactions Table, downloadable IGCSE & GCSE Chemistry revision notes

  • The following are some specific examples of reactions  between acids and metal carbonates:

2HCl + Na2CO3 ⟶ 2NaCl + H2O + CO2

H2SO4 + CaCO3⟶ CaSO4 + H2O + CO2

Exam Tip

If in an acid-base reaction there is effervescence produced then the base must be a metal carbonate which produces carbon dioxide gas.

Predicting the Salts

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

Naming Salts Table, downloadable 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 is 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

Worked Example

What is the formula of magnesium phosphate?

Answer

Step 1: Write out the formulae of each ion, including their charges

Mg2+ and PO43-

Step 2: 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

Exam Tip

You should know by heart the names of the common ions, their charges and the formulae compounds they often appear in.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top