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(a) Define the following terms with an example :
(i) Roasting
(ii) Alloy
(iii) Corrosion
(i) Roasting
(ii) Alloy
(iii) Corrosion
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(a) (i) The conversion of sulphide ore into oxide by heating strongly in the presence of excess air. ($\frac{1}{2}$ Mark)
$\ce{2ZnS(s) + 3O2(g) ->[Heat] 2ZnO(s) + 2SO2(g)}$ ($\frac{1}{2}$ Mark)
(Or any other example)
(ii) • An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. ($\frac{1}{2}$ Mark)
• Example Brass ($\frac{1}{2}$ Mark)
(or any other)
(iii) The slow and gradual degradation of metals due to their reaction with moisture, acids etc. present in the atmosphere is called corrosion ($\frac{1}{2}$ Mark)
Example: Formation of $\ce{Fe2O3.xH2O}$ (Rust) or silver sulphide on silver articles. ($\frac{1}{2}$ Mark)
(any one or any other) (3 Marks)
$\ce{2ZnS(s) + 3O2(g) ->[Heat] 2ZnO(s) + 2SO2(g)}$ ($\frac{1}{2}$ Mark)
(Or any other example)
(ii) • An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. ($\frac{1}{2}$ Mark)
• Example Brass ($\frac{1}{2}$ Mark)
(or any other)
(iii) The slow and gradual degradation of metals due to their reaction with moisture, acids etc. present in the atmosphere is called corrosion ($\frac{1}{2}$ Mark)
Example: Formation of $\ce{Fe2O3.xH2O}$ (Rust) or silver sulphide on silver articles. ($\frac{1}{2}$ Mark)
(any one or any other) (3 Marks)