Higher and foundation tier

Metal acid reactions

Metals react with dilute acids according to the equation below:
metal(s) + acid(aq) → salt(aq) + hydrogen(g)

The image below shows the reactions of metals magnesium, zinc, iron, tin, lead and copper with dilute acid. It would be foolish to add any of the alkali metals from group 1 of the periodic table to acids as the reactions with water are violent enough, so adding them to acid would be considered too dangerous in a classroom, as the reactions are likely to be violent or explosive. For the reactions shown in the image you can measure the rate or speed of the reaction by measuring how quickly the hydrogen gas is produced or even a simple thermometer would give an indication of the amount of energy released and the speed of the reaction.

metal acid reactions You can see that the most bubbles are produced by magnesium and that the metals become less reactive as we move from magnesium to zinc all the way down to the unreactive copper metal.

Equations for reactions

You should already know that:

Acid Formula Salt formed
hydrochloric HCl chloride
sulfuric H2SO4 sulfate
nitric HNO3 nitrate

Using hydrochloric acid

1. magnesium

magnesium(s) + hydrochloric acid(aq) magnesium chloride(aq) + hydrogen(g)
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2 (g)

2. calcium

calcium(s) + hydrochloric acid(aq) calcium chloride(aq) + hydrogen(g)
Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)

You can see that hydrochloric acid always produces salts called chlorides

Using sulfuric acid

1. magnesium

magnesium(s) + sulfuric acid(aq) magnesium sulfate(aq) + hydrogen(g)
Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g)

2. calcium

calcium(s) + sulfuric acid(aq) calcium sulfate(aq) + hydrogen(g)
Ca(s) + H2SO4(aq) → CaSO4(aq) + H2(g)

You can see that sulfuric acid always produces salts called sulfate

Using nitric acid

1. magnesium

magnesium(s) + nitric acid(aq) magnesium nitrate(aq) + hydrogen(g)
Mg(s) + 2HNO3(aq) → Mg(NO3)2(aq) + H2(g)

You can see that nitric acid always produces salts called nitrate

In each of the reactions of the metal with acid the metal is oxidised, that is they lose electrons e.g. Consider the metal magnesium, it is an alkaline earth metal in group 2 of the periodic table, this means it has 2 electrons in its last shell, so it will lose these in its reactions to form a metal ion with a 2+ charge.

Mg(s) → Mg2+(aq) + 2e
this is an oxidation reaction.
the acid contains H+(aq) ions and these gain electrons and form hydrogen gas:
2H+(aq) + 2e → H2(g)
this is a reduction reaction.
The metal is oxidised and the hydrogen ions are reduced, so this is an example of a redox reaction. A redox reaction is one where one substance is reduced (gains electrons) and another substance is oxidised (loses electrons)

Practice questions

Check your understanding - Questions on metal acid reactions

Key Points


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