(a)(i) Structure of the sixth member of the alkenes: C\(_n\)H\(_{2n}\); n = 7, C\(_7\)H\(_{2 \times 7}\) = C\(_7\)H\(_14\)

(Double can be positioned within any of the carbon chain)

(ii) Relative molecular mass of the sixth member of alkene

(C\(_7\)H\(_14\) \(\begin {bmatrix} C & = 12 \\ H & = 1 \end{bmatrix}\)

(C\(_7\)H\(_14\) = (12 x 7) + (1 x 14)

= (12 x 7) + (1 x 14)

= 84 + 14

= 98 (no units)

(iii) One differences between cracking and reforming in the petroleum indutry:

CRACKING

Involves breaking large molecules of petroleumfractions into smaller molecules

Usect to improve the quantity of petrol.

Can be achieved thermally or catalytically


REFORMING

Involves re-arrangement of atoms in molecules of petroleum fractio'n to obtain branched and cyclic hydrocarbons

Usect to improve the quality of petrol.

Occurs in presence of a catalyst




Occurs in presence of a catalyst
(b)(i) Enthalpy of neuttalization is the beat evolved when an acid reacts with a base to form one mole of water or when one mole of OH\(^{+}\) from an acid reacts with one mole of OH\(^{-}\) from a base to form one mole of water.

(ii) Determination of enthalpy of neutralization of the reaction of dilute hydrochloric acid and aqueous potassium hydroxide

HCI\(_{(aq)}\)+ KOH\(_{(aq)}\) -> KC1 + H\(_{2}\)O

Equimolar solutions of hydrochloric acid and potassium hydroxide are prepared sepa'rately. A known volume of the acid is placed in a calorimeter/polystyrene beaker and the temperature recorded.

The same volume of the potassium hydroxide solution at the same temperature is poured into the calorimeter and the mixture stirred gently. The maximum temperature of the mixture is recorded.

Heat lost in the reaction = heat gained by the solution formed

OR \(\bigtriangleup\) H neutralization = mass of solution x specific heat capacity of water x change in temperature.



(c) An electrochemical cell connected with copper and silver electrodes. (i) A node : copper electrode

(ii) Cathode : silver electrode reasons in 3(c)(i)

(iii) Silver has a more positive Standard electrode potential than copper. Copper is more electropositive than silver or copper is higher in the electrochemical series

(iv) Type of reaction occuring at each electrode.

Anode : oxidation (occurs at the copper electrode).

Cathode : reduction (occurs at the siliver electrode).

(v) Balanced chemical equation for the overall cell reaction.

Cu\(_s\) + 2Ag\(^+\) \(\to\) CU\(^{2+}_{(aq)}\) + 2Ag\(_(s)\)



(d) Compound formed when iron is exposed to moist air for a long time; (i) Hydrated Iron(III) oxide. (ii) Balanced chemical equation for the reaction in 3(d)(i).

4Fe\(_s\) + 3O\(_{2(g)}\) + 2 x H\(_2\)O\(_l\) \(\to\) 2Fe\(_2\)O\(_3\).XH\(_2\)O

where X is 1

4Fe\(_s\) + 3O\(_{2(g)}\) + 2H\(_2\)O\(_l\) \(\to\) 2Fe\(_2\)O\(_3\).H\(_2\)O

(iii) One ore of iron: haematite, magnetite, siderite/spathic iron ore, limonite, iron pyrites