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 the 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 environment since 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 from the image that the fastest reaction is with the 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

• 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:

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

Below are word and symbolic equations for the reactions of acids with metals. If you need help with working out the formulae for acids then visit the page on finding the formula. You should also read the page on acids if you are unsure of the properties of acids and salts.

### Reactions of metals and hydrochloric acid

#### 2. calcium

##### Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)

You can see that hydrochloric acid always produces salts called chlorides

### Using sulfuric acid

#### 2. calcium

##### Ca(s) + H2SO4(aq) → CaSO4(aq) + H2(g)

You can see that sulfuric acid always produces salts called sulfate

### Using nitric acid

#### 1. magnesium

##### 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)

## Key Points

• 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 the metal
• Metal acid reactions involve oxidation and reduction reactions and so are redox reactions.