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First teaching 2023

First exams 2025

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Neutralisation Reactions (SL IB Chemistry)

Revision Note

Philippa Platt

Last updated

Neutralisation Reactions

  • A neutralization reaction is one in which an acid (pH <7) and a base/alkali (pH >7) react together to form water (pH = 7) and a salt:

acid + base (alkali) → salt + water

  • The proton of the acid reacts with the hydroxide of the base to form water:

H+ (aq) + OH → H2O (l)

  • The spectator ions which are not involved in the formation of water, form the salt

Diagram to show neutralisation between an acid and a base

Diagram to show neutralisation between an acid and a base

The diagram shows a neutralisation reaction of HCl and NaOH and the two individual reactions that take place to form the water and salt

  • The name of the salt produced can be predicted from the acid that has reacted

Acid Reacted & Salt Table

Acid reacted Salt produced
Hydrochloric acid A chloride
Nitric acid A nitrate
Sulfuric acid A sulfate

Examiner Tip

  • The enthalpy of neutralisation is the enthalpy change that occurs when an acid reacts with a base to form one mole of water
  • Since the reaction between strong acids and strong bases is the same regardless of the acid or base, it should be no surprise the enthalpy change is the same and is approximately -57 kJ mol-1

Metals and acids

  • The typical reaction of a metal and an acid can be summarised as

acid + metal    salt + hydrogen

  • For example:

2HCl (aq) + Zn (s)  ZnCl2 (aq) + H2 (g)

hydrochloric acid + zinc   zinc chloride + hydrogen

  • Clearly, the extent of the reaction depends on the reactivity of the metal and the strength of the acid
  • Very reactive metals would react dangerously with acids and these reactions are not usually carried out
  • Metals low in reactivity do not react at all
    • For instance, copper does not react with dilute acids
  • Stronger acids will react more vigorously with metals than weak acid
  • What signs of reaction would be expected to be different between the two?
    • Faster reaction, seen as:
      • More effervescence
      • The metal dissolves faster
      • More exothermic

Metals and oxides

  • The reaction of an acid with a metal oxide forms two products:

acid + metal oxide   salt + water

  • For example:

2HCl (aq) + CaO (s) → CaCl2 (aq) + H2O (l)

hydrochloric acid + calcium oxide →  calcium chloride + water

Metals and hydroxides

  • The reaction with a metal hydroxide and an acid follows the same pattern as an oxide:

acid + metal hydroxide   salt + water

  • A suitable example might be:

H2SO(aq) + Mg(OH)2 (s) → MgSO(aq) + 2H2O (l)

sulfuric acid + magnesium hydroxide → magnesium sulfate + water

Metals and carbonates

  • The reaction between a metal carbonate and an acid produces three products:

acid + metal carbonate  salt + water + carbon dioxide

  • For example:

2HNO(aq) + CuCO(s) → Cu(NO3)2 (aq) + H2O (l) + CO2 (g)

nitric acid + copper carbonate → copper nitrate + water + carbon dioxide

Metals and hydrogencarbonates

  • The reaction between a metal hydrogencarbonate and an acid is the same as the carbonate reaction with a slight difference in stoichiometry:

acid + metal hydrogencarbonate  salt + water + carbon dioxide

  • An example of this would be:

HCl (aq) + NaHCO3 (s) → NaCl (aq) + H2O (l) + CO2 (g)

hydrochloric acid  + sodium hydrogencarbonate  → sodium chloride + water + carbon dioxide

Examiner Tip

Make sure you learn the formulae of the common acids and bases and that you can write examples of balanced equations of their characteristic reactions

  • The acids and bases needed to make different salts can be deduced using the principles covered in the previous section
  • The table below summarises these reactions

Making Salts Table

Type of salt Ion Acid needed Formula Base needed
Sulfates SO42– sulfuric H2SO4 metal oxide, hydroxide, carbonate or hydrogen carbonate
Nitrates NO3 nitric HNO3
Chlorides Cl hydrochloric HCl
Ethanoates CH3COO ethanoic CH3COOH
Ammonium NH4+ any - aqueous ammonia

Note that although some metals can be used to make salts, they are not classified as bases as water is not a product of the reaction

Worked example

Which are the products of the reaction between zinc oxide and hydrochloric acid?

   A. zinc chloride and carbon dioxide

   B. zinc chloride, hydrogen gas and water

   C. zinc, hydrogen gas and water

   D. zinc chloride and water

 

Answer:

  • The correct option is D.
    • Metal oxides react with acids to produce a salt and water as the only products

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Philippa Platt

Author: Philippa Platt

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.