Question

(a) Write names and formulae of hydrocarbons containing a single and a double bond (one example for each). Give one characteristic chemical property of each.
(b) What is a detergent? Name one detergent.
(c) Why have detergents replaced soap as a washing agent?

Answer 1

a) Methane is a hydrocarbon which has a single bond. Its formula is CH₄.
The characteristic chemical property of methane is the substitution reaction. It is a reaction in which one or more hydrogen atoms are replaced by some other atoms.

Chemical equation:
${\mathrm{CH}}_4+{\mathrm{Cl}}_2\stackrel{\mathrm{sunlight}}{\to }{\mathrm{CH}}_3\mathrm{Cl}+\mathrm{HCl}$

Ethene is a hydrocarbon containing a double bond. Its formula is C₂H_4.
The characteristic chemical property of ethene is the addition reaction. It is a reaction in which unsaturated compound (ethene) is combined with another substance to form a single product (saturated compound).

Chemical equation:
${\mathrm{CH}}_2={\mathrm{CH}}_2+{\mathrm{H}}_2\underset{\mathrm{Heat}}{\overset{\mathrm{Ni}\mathrm{catalyst}}{\to }}{\mathrm{CH}}_3-{\mathrm{CH}}_3$

(b) Detergent, a sodium salt of a long chain benzene sulphonic acid, is a cleansing agent. It has cleansing properties in water. A detergent has two parts, a large non-ionic hydrocarbon group and an ionic group such as sulphonate group SO₃^-Na⁺. Name of a detergent is sodium n-dodecyl benzene sulphonate.

(c) Detergents have replaced soap as a washing agent because they do not form insoluble calcium and magnesium salts (scum) in hard water. Solubility of detergents, even in hard water, is better than a soap. Detergents also froth well.