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.
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:
- all acids contain hydrogen ions, H+(aq).
- salts are solids formed when the hydrogen in the acid is replaced
by a metal.
(sometimes it maybe ammonium ions (see section on ammonia)
- The name of the salt depends on the acid used, as shown in the table below:
Using hydrochloric acid
magnesium(s) + hydrochloric acid(aq) → magnesium chloride(aq) + hydrogen(g)
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2 (g)
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
magnesium(s) + sulfuric acid(aq) → magnesium sulfate(aq) + hydrogen(g)
Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g)
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
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
the acid contains H+(aq) ions and these gain electrons and form hydrogen gas:
this is an oxidation reaction.
2H+(aq) + 2e → H2(g)
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)
this is a reduction reaction.
- Some metals will react with acids to form a salt and release hydrogen gas.
- The salt formed depends on which acid is used. Hydrochloric acid forms salts called chlorides,
sulfuric acid forms sulfates and
nitric acid forms nitrates.
- Metal atoms are oxidised and lose electrons when they react with
acids. The acids are reduced and gain the electrons from
- Metal acid reactions involve oxidation and
reduction reactions and so are redox reactions.