Question

1. (a) define the term polymerization.

(b) state three characteristics of an equilibrium reaction.
(c) explain briefly why the reaction of dilute h₂so₄ with solid caco₃ stops after sometime.
(d) (i) what is meant by the statement matter is particulate.
(ii) name two of the building blocks of matter.
(e) explain briefly why a mixture of sodium chloride and ammonium chloride can be separated by sublimation.
(f) (i) state the property of a substance that makes it paramagnetic.
(ii) state the difference between a pure covalent bond and a co - ordinate bond.
(g) state two of the assumptions that are made in order to explain the behaviour of gases.
(h) (i) name the concept of acids and bases that deals with non - aqueous systems.
(ii) define an acid and a base under the concept named in (i).
(i) a solid sample does not conduct electric current. suggest two ways by which it can be made to conduct electric current.
(j) write balanced nuclear equations to represent each of the following states:
(i) ₂₃₅₉₂u undergoes α - particle emission to produce element x.
(ii) x also undergoes β - particle emission to produce element y.

Explanation:

(a) Polymerization is the process by which small molecules (monomers) combine to form large - chain or network - like molecules (polymers).
(b) Characteristics of an equilibrium reaction: 1. Forward and reverse reactions occur at equal rates. 2. Concentrations of reactants and products remain constant over time. 3. It is a dynamic process at the molecular level.
(c) The reaction of dilute $H_2SO_4$ with solid $CaCO_3$ stops because the product $CaSO_4$ forms a coating on the surface of $CaCO_3$, preventing further contact between the acid and the solid.
(d)(i) Matter is particulate means that matter is made up of discrete particles such as atoms, molecules or ions. (ii) Two building blocks of matter are atoms and molecules.
(e) A mixture of sodium chloride and ammonium chloride can be separated by sublimation because ammonium chloride sublimes (changes directly from solid to gas) on heating while sodium chloride does not.
(f)(i) A substance is paramagnetic if it has unpaired electrons. (ii) In a pure covalent bond, electrons are shared equally between atoms. In a co - ordinate bond, the shared pair of electrons is provided entirely by one atom.
(g) Assumptions for gas behavior: 1. Gas molecules are in constant random motion. 2. There are no intermolecular forces between gas molecules (except during collisions).
(h)(i) The concept of acids and bases for non - aqueous systems is the Lewis concept. (ii) A Lewis acid is an electron - pair acceptor and a Lewis base is an electron - pair donor.
(i) A non - conducting solid sample can be made to conduct by melting it (if it is an ionic solid) to free the ions for conduction or by doping (if it is a semiconductor).
(j)(i) The $\alpha$-particle emission of $^{235}_{92}U$: $^{235}_{92}U
ightarrow^{231}_{90}Th + ^{4}_{2}He$. (ii) If $X = ^{231}_{90}Th$, its $\beta$-particle emission: $^{231}_{90}Th
ightarrow^{231}_{91}Pa+^{0}_{ - 1}e$.

Answer:

(a) Polymerization is the combination of monomers to form polymers.
(b) Equal forward and reverse rates; constant concentrations; dynamic at molecular level.
(c) $CaSO_4$ coating prevents further reaction.
(d)(i) Matter is made of discrete particles. (ii) Atoms, molecules.
(e) Ammonium chloride sublimes, sodium chloride does not.
(f)(i) Presence of unpaired electrons. (ii) In pure covalent, electrons shared equally; in co - ordinate, one atom provides shared pair.
(g) Constant random motion; no intermolecular forces (except during collisions).
(h)(i) Lewis concept. (ii) Lewis acid: electron - pair acceptor; Lewis base: electron - pair donor.
(i) Melt it (if ionic); dope it (if semiconductor).
(j)(i) $^{235}_{92}U
ightarrow^{231}_{90}Th + ^{4}_{2}He$ (ii) $^{231}_{90}Th
ightarrow^{231}_{91}Pa+^{0}_{ - 1}e$