(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 = 5.02 x 10\(^{23}\)
(a)(i) Two transition-metal properties of iron: it exhibits variable oxidation states (Fe2+ and Fe3+) and it forms coloured compounds (it also acts as a catalyst, e.g. in the Haber process).
(a)(ii) Extraction of iron in the blast furnace (equations):
\[ \text{C} + \text{O}_2 \to \text{CO}_2 \]
\[ \text{CO}_2 + \text{C} \to 2\text{CO} \]
\[ \text{Fe}_2\text{O}_3 + 3\text{CO} \to 2\text{Fe} + 3\text{CO}_2 \]
Removal of impurities (limestone decomposes and the lime removes the silica gangue as slag):
\[ \text{CaCO}_3 \to \text{CaO} + \text{CO}_2 \]
\[ \text{CaO} + \text{SiO}_2 \to \text{CaSiO}_3\ (\text{slag}) \]
(a)(iii) Prevention of rusting (three methods): painting the surface; coating with oil/grease; galvanising (coating with zinc) or electroplating; sacrificial protection with a more reactive metal.
(a)(iv) The product is Fe2O3; the oxidation number of iron in it is +3.
(b)(i) Increasing reactivity: Au < Sn < Zn < Mg < Ca < Na. Those extracted by electrolysis are the most reactive: Na, Ca and Mg.
(b)(ii) Zinc is amphoteric because it (and its oxide/hydroxide) reacts with both acids and alkalis to form a salt and water.
(c)(i) Oxidation: the loss of electrons by a species.
(c)(ii) Moles of electrons \(= \dfrac{Q}{F} = \dfrac{4825}{96500} = 0.05\ \text{mol}\).
(c)(iii) For \(\text{Cu}^{2+} + 2e^- \to \text{Cu}\), 0.250 F provides 0.250 mol of electrons, discharging \(\dfrac{0.250}{2} = 0.125\ \text{mol}\) of Cu2+.
\[ \text{Number of ions} = 0.125 \times 6.02\times10^{23} = 7.53\times10^{22}\ \text{ions} \]
(a)(i) Two transition-metal properties of iron: it exhibits variable oxidation states (Fe2+ and Fe3+) and it forms coloured compounds (it also acts as a catalyst, e.g. in the Haber process).
(a)(ii) Extraction of iron in the blast furnace (equations):
\[ \text{C} + \text{O}_2 \to \text{CO}_2 \]
\[ \text{CO}_2 + \text{C} \to 2\text{CO} \]
\[ \text{Fe}_2\text{O}_3 + 3\text{CO} \to 2\text{Fe} + 3\text{CO}_2 \]
Removal of impurities (limestone decomposes and the lime removes the silica gangue as slag):
\[ \text{CaCO}_3 \to \text{CaO} + \text{CO}_2 \]
\[ \text{CaO} + \text{SiO}_2 \to \text{CaSiO}_3\ (\text{slag}) \]
(a)(iii) Prevention of rusting (three methods): painting the surface; coating with oil/grease; galvanising (coating with zinc) or electroplating; sacrificial protection with a more reactive metal.
(a)(iv) The product is Fe2O3; the oxidation number of iron in it is +3.
(b)(i) Increasing reactivity: Au < Sn < Zn < Mg < Ca < Na. Those extracted by electrolysis are the most reactive: Na, Ca and Mg.
(b)(ii) Zinc is amphoteric because it (and its oxide/hydroxide) reacts with both acids and alkalis to form a salt and water.
(c)(i) Oxidation: the loss of electrons by a species.
(c)(ii) Moles of electrons \(= \dfrac{Q}{F} = \dfrac{4825}{96500} = 0.05\ \text{mol}\).
(c)(iii) For \(\text{Cu}^{2+} + 2e^- \to \text{Cu}\), 0.250 F provides 0.250 mol of electrons, discharging \(\dfrac{0.250}{2} = 0.125\ \text{mol}\) of Cu2+.
\[ \text{Number of ions} = 0.125 \times 6.02\times10^{23} = 7.53\times10^{22}\ \text{ions} \]
