Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) 4Na(s) + O2 (g) → 2Na2O(s)
(ii) CuO(s) + H2 (g) → Cu(s) + H2O(l)
Answer:
(i) 4Na(s) + O₂(g) → 2Na₂O(s)
Step-by-step:
Sodium (Na) reacts with oxygen (O₂) to form sodium oxide (Na₂O).
In this process:
Sodium gains oxygen → it is oxidised.
Oxygen combines with sodium, but we focus on sodium’s change here.
- Oxidised: Sodium (Na)
- Reduced: Oxygen (O₂)
(ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)
Step-by-step:
Copper(II) oxide (CuO) reacts with hydrogen (H₂) to form copper (Cu) and water (H₂O).
In this process:
CuO loses oxygen → Cu is reduced.
Hydrogen gains oxygen → H₂ is oxidised.
- Oxidised: Hydrogen (H₂)
- Reduced: Copper(II) oxide (CuO)