(a)(i) Draw the structure of the sixth member of the alkenes. (ii) Calculate the relative molecular mass of the sixth member of the alkene. (iii) State one ...

(a)(i) Alkenes have the general formula \(\mathrm{C_nH_{2n}}\). Starting from ethene as the first member, the sixth member is heptene, \(\mathrm{C_7H_{14}}\). One correct structure is hept-1-ene:

(ii)

(iii) Cracking breaks large hydrocarbon molecules into smaller molecules, whereas reforming rearranges straight-chain hydrocarbons into branched-chain or cyclic hydrocarbons to improve petrol quality.

(b)(i) The enthalpy of neutralization is the enthalpy change when one mole of water is formed by the reaction of an acid with a base in dilute aqueous solution.

(ii) Prepare equimolar dilute hydrochloric acid and aqueous potassium hydroxide. Measure a known volume of the hydrochloric acid into a polystyrene cup calorimeter and record its initial temperature. Measure an equal volume of potassium hydroxide at the same initial temperature, add it quickly to the acid, stir, and record the maximum temperature reached.

Calculate the heat gained by the solution using \(q=mc\Delta T\), where \(m\) is the mass of the mixed solution and \(c=4.18\ \mathrm{J\,g^{-1}\,K^{-1}}\). Since neutralization is exothermic, the heat of reaction is \(-q\). Divide this value by the number of moles of water formed to obtain the enthalpy of neutralization:

(c)(i)

1. Anode: copper electrode.
2. Cathode: silver electrode.

(ii) Copper is more electropositive, or higher in the electrochemical series, than silver. Therefore copper loses electrons more readily, while \(\mathrm{Ag^+}\) ions gain electrons more readily.

(iii) Oxidation occurs at the copper anode and reduction occurs at the silver cathode.

(iv)

(d)(i) The compound formed is rust, hydrated iron(III) oxide, \(\mathrm{Fe_2O_3\cdot xH_2O}\).

(ii)

(iii) Haematite, \(\mathrm{Fe_2O_3}\), is an ore of iron.