Why should a magnesium ribbon be cleaned before burning in the air?

Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with the atmospheric oxygen and forms Magnesium Oxide (MgO) layer which is a very stable compound. In order to prevent further reactions with Oxygen, it is therefore necessary to clean the ribbon by to remove the layer of MgO.

1. Write a balanced equation for the following chemical reactions.
2. i) Hydrogen + Chloride —-> Hydrogen chloride
3. ii) Barium chloride + Aluminium sulphate —-> Barium sulphate + Aluminium chloride

iii) Sodium + Water —-> Sodium hydroxide + Hydrogen

Solution:

1. i) H₂ + Cl₂ → 2HCl
2. ii) 3BaCl₂ + Al₂(SO₄)₃ →3BaSO₄ + 2AlCl₃ 

iii) 2Na + 2H₂O → 2NaOH + H₂