Neutralisation Reactions (DP IB Chemistry)

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

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

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:

H₂SO₄ (aq) + Mg(OH)₂ (s) → MgSO₄ (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:

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

• The table below summarises these reactions

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