Learning focus
Develop precise chemical language, connect equations and practical observations, interpret periodic trends and apply salt-preparation rules to unfamiliar examples.
Meaning of neutralisation
Neutralisation is a reaction between an acid and a base. In an acid-alkali reaction, hydrogen ions react with hydroxide ions to form water. The accompanying ions form the dissolved salt.
Net ionic equation
H+(aq) + OH-(aq) -> H2O(l). This equation removes spectator ions, which are present but unchanged. It applies to strong acid-strong alkali combinations because both provide the ions shown.
Equivalence and neutrality
At the equivalence point, stoichiometric acid and base amounts have reacted. For a strong acid and strong alkali, pH is close to 7. In broader chemistry, equivalence need not always mean pH 7, so avoid turning this example into a universal rule.
Energy transfer
Formation of water from H+ and OH- releases thermal energy. An insulated-cup experiment can measure temperature rise. Fair comparison requires equal total volumes, known concentrations and the same initial temperature.
Practical or data skill
Mix measured acid and alkali volumes in an insulated cup and record the highest temperature. Use indicator only in a separate endpoint trial if pure salt solution is needed.
Examination tip
Spectator ions do not appear in the net ionic equation.
Review questions and suggested answers
Question 1
Write the neutralisation ionic equation.
Suggested answer
H+(aq) + OH-(aq) -> H2O(l).
Question 2
What are spectator ions?
Suggested answer
Ions present in solution that do not change during the reaction.
Question 3
Why may temperature rise?
Suggested answer
Neutralisation is exothermic.
