Get premium membership and access revision papers with marking schemes, video lessons and live classes.

Processing. Please wait.

Burning non-metals in oxygen

Answer Text:
Burning non-metals in oxygen
Requirements:
- Non-metals; deflagrating spoon; gas jar; source of heat;
Diagram of apparatus;
Procedure:
- A piece of sulphur is heated on a deflagrating spoon until it begins to burn;
- It is then lowered into a gas jar of oxygen as shown above;
- The flame colour is noted;
- The gas jar is allowed to cool; some water added to the product(s) in the gas jar and shook well;
- Any resultant solution is tested with litmus papers;
- Any gases produced are tested by smell and also with litmus papers;
- The experiment is then repeated with pure oxygen;
- The whole procedure is repeated with other nonmetals such as carbon and phosphorus;
Explanations:
1. Sulphur.
- Burns in oxygen with a blue flame to give a colourless gas with a choking irritating smell;
- The gas is sulphur (IV) oxide;
Equation:
Sulphur + Oxygen → Sulphur (IV) oxide;
`S + O_2(g) → SO_2(g)`;
- The sulphur (IV) oxide dissolves in water to form sulphurous acid, which turns litmus rd;
`SO_2(g) + H_2O(l) → H_2SO_3(l)`;
2. Carbon
- Glows red to give a colourless gas that forms a white precipitate in lime water;
- The gas is Carbon (IV) oxide;
Equation:
Carbon + Oxygen → Carbon (IV) oxide;
`C + O_2(g) → CO_2(g)`;
- The Carbon (IV) oxide dissolves in water to form weak carbonic acid, which turns litmus rd;
`CO_2(g) + H_2O(l) → H_2CO_3(l)`;
Note:
- In limited oxygen the carbon undergoes partial oxidation forming carbon (II) oxide;
Equation:
`2C(s) + O_2(g) → 2CO(g)`
3. Phosphorus.
- Burns in oxygen with a white flame to give dense white fumes;
- The white fumes are either phosphorus (V) oxide or phosphorus (III) oxide;
- Both solids // fumes dissolve in water to form phosphoric acid;
Equations:
With limited supply of oxygen:
Phosphorus + Oxygen → Phosphorus (III) oxide;
`P_4(s) + 3O_2(g) →2P_2O_3(g)`;
With excess oxygen.
Phosphorus + Oxygen → Phosphorus (V) oxide;
`P_4(s) + 5O_2(g) →P_2O_10(g)`;