(a)(i) List two properties of iron that are characteristic of transition metals
(ii) Using equations only, show the processes involved in the extraction of iron and the removal of impurities in the blast furnace.
(iii) The following reaction occurs when a piece of iron is exposed to moist air for some days:
4Fe\(_{(s)}\) + 3O\(_{2(g)}\) + xH\(_2\)O\(_{(l)}\) —> 2Fe\(_2\)O\(_3\)\(_{(s)}\) State three methods by which this reaction can be prevented
(iv) What is the oxidation number of iiron in the product in (iii) above?
(b)(i) Arrange the following metals in the order of increasing reactivity. Hence, state which of them is/are extracted by electrolysis Au, Zn, Mg, Na, Sn, Ca
(ii) Why is zinc said to be amphoteric?
(c)(i) Define oxidation in term of electron transfer
(ii) Determine how many moles of electrons are transferred when 4825 coulombs of electricity are passed through an electrolytic cell. [1F = 96500C]
(iii) Calculate the number of copper (II) ions that will be discharged by 0.250F. [Avogadro constant = 6.02 x 10\(^{23}\)
Explanation
(a)(i) Variable oxidation states (oxidation states of +2 or +3) formation of coloured ions (green or brown) Catalytic ability e.g (in the Haber process) formation of complex ions e.g K\(_4\)Fe (CN)\(_6\). Ability to be magnetised strongly (Ferromagnetism / paramagnetism).
(ii) C + O\(_2\) --> CO\(_2\) CO + C \(\to\) CO Fe\(_2\)O\(_3\) + 3CO \(\to\) 2Fe + 3CO\(_2\)
or Fe\(_2\)O\(_3\) + 3C \(\to\) 2Fe + 3CO CaCO\(_3\) \(\to\) CaO + CO\(_2\) CaO + SiO\(_2\) \(\to\) CaCO\(_3\)
(iii) The reaction of iron to produce rust (Fe\(_3\)O\(_2\) x H\(_2\)O) can be prevented by galvanising, painting, electroplating, greasing or oiling, cathodic protection or anodic sacrificing.
(iv) The oxidation number of iron in iron rust is +3.
(b)(i) Au, Sn, Zn, Mg, Ca, Na in order of reactivity. Mg, Ca, and Na are extracted by electrolysis
(ii) Zinc is said to be amphoteric because it can react with acids and with bases to form salts.
(c)(i) Oxidation is loss of electrons
(ii) If or 96500C is equivalent to 1 mole of electrons
4825 C = \(\frac{4825}{96500}\) moles = 0.05 mole
(iii) 1 mole of Cu\(^{2+}\) is discharged by 2F. 1 mole of Cu\(^{2+}\) contains 6.02 x 10\(^{23}\) ions
6.02 x 10\(^{23}\) copper ions is 6.02 x 10\(^{23}\) discharged by 2F.
Hence ; 0.25 ions will be discharged by 0.25
F = 7.53 x 10\(^{22}\)