Question

Write short notes on the following:

[(a)] Roasting
[(b)] Double Decomposition
[(c)] Corrosion

Hint:

Roasting is used in metallurgy, double decomposition in salt reactions, and corrosion prevention is important for protecting metal structures.

Answer 1

(a) Roasting:
Roasting is a process in metallurgy in which a sulphide ore is strongly heated in the presence of excess air to convert it into its oxide form. \[ \text{Example: } 2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2 \] It helps in removing volatile impurities and prepares the ore for reduction.
(b) Double Decomposition:
Double decomposition is a type of chemical reaction in which two compounds react by exchanging ions to form two new compounds. It often occurs in aqueous solution and may result in a precipitate, gas, or water. \[ \text{Example: } Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 \downarrow + 2NaCl \]
(c) Corrosion:
Corrosion is a slow process where metals are gradually destroyed by reaction with atmospheric moisture, acids, or gases. For example, iron reacts with oxygen and water to form rust. \[ \text{4Fe + 3O}_2 + \text{6H}_2\text{O} \rightarrow 4Fe(OH)_3 \text{ (rust)} \] It leads to weakening and damage of metal objects over time.