(a)(i) List two uses of aluminium and state how each use is related to the properties of the element. (ii) State the reason why aluminium oxide is said to b...
Question 1 Report
(a)(i) List two uses of aluminium and state how each use is related to the properties of the element.
(ii) State the reason why aluminium oxide is said to be amphoteric.
(b) Calcium is extracted by the electrolysis of fused calcium chloride containing about one-sixth of its mass of calcium fluoride.
(i) Sketch and label the cell used for the extraction.
(ii) Write equations for the reactions at the electrodes.
(iii) State the role of the calcium fluoride in the extraction.
(c) W, X, Y and Z represent four metals which have the following properties: W does not react with cold water but it liberates hydrogen from steam; X is one of the products formed when its trioxonitrate (V) decomposes on strong heating; Z forms the oxide when heated in air and it displaces W from an aqueous solutions of a salt of W; Y tarnishes rapidly exposure and reacts vigorously with cold water. Use the information provided to deduce the order of reactivity of the metals.
Answer Details
(a)(i) Uses of aluminium and related properties
- Cooking utensils: aluminium is a good conductor of heat, is light, and resists attack by food because of its protective oxide coating.
- Overhead electric cables: aluminium is a good conductor of electricity and has low density, making the cables light.
(a)(ii) Aluminium oxide is amphoteric because it reacts with both acids and bases.
With an acid:
\[Al_2O_3 + 6HCl \rightarrow 2AlCl_3 + 3H_2O\]
With a base:
\[Al_2O_3 + 2NaOH + 3H_2O \rightarrow 2NaAl(OH)_4\]
(b)(i) Electrolytic cell for extracting calcium
(b)(ii) Electrode reactions
At the cathode:
\[Ca^{2+} + 2e^- \rightarrow Ca\]
At the anode:
\[2Cl^- \rightarrow Cl_2 + 2e^-\]
(b)(iii) Calcium fluoride lowers the melting point of calcium chloride. This allows electrolysis to take place at a lower temperature and hence reduces energy required.
(c) The order of reactivity, starting with the least reactive metal, is:
\[\boxed{X < W < Z < Y}\]
Equivalently, in decreasing order of reactivity: \(Y > Z > W > X\).
- Y reacts vigorously with cold water and is therefore the most reactive.
- Z displaces W from a solution of a salt of W, so Z is more reactive than W.
- W reacts with steam but not with cold water.
- X is produced when its trioxonitrate(V) is strongly heated, showing that it is the least reactive.
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