Neutralisation Reactions (DP IB Chemistry): Revision Note

Neutralisation reactions

• A neutralisation 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

• For example:

HCl (acid) + NaOH (base) → H₂O (water) + NaCl (salt)

• The two individual reactions taking place are:

  • H⁺ + OH⁻ → H₂O

  • Na⁺ + Cl⁻ → NaCl

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

Acid reacted & salt summary

• Hydrochloric acid form chlorides

• Nitric acid form nitrates

• Sulfuric acid form sulfates

Metals and acids

• The general equation is:

acid + metal  →  salt + hydrogen

• For example:

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

hydrochloric acid + zinc →  zinc chloride + hydrogen

• The reaction rate depends on:

  • The reactivity of the metal

  • The strength of the acid

• Highly reactive metals can react dangerously with acids, so these are often avoided

• Unreactive metals (e.g. copper) do not react with dilute acids

• Stronger acids react more vigorously, producing:

  • More effervescence

  • Faster metal dissolution

  • Greater exothermic effect

Metals and oxides

• The general equation is:

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 general equation is:

acid + metal hydroxide →  salt + water

• A suitable example might be:

H₂SO₄ (aq) + Mg(OH)₂ (s) → MgSO₄ (aq) + 2H₂O (l)

sulfuric acid + magnesium hydroxide → magnesium sulfate + water

Metals and carbonates

• The general equation is:

acid + metal carbonate → salt + water + carbon dioxide

• For example:

2HNO₃ (aq) + CuCO₃ (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

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

Making salts table

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