The table shows results from a materials trial for the inside wall of a furnace used to heat iron oxide. The lining must remain solid at a high temperature,...
Question 1 Report
The table shows results from a materials trial for the inside wall of a furnace used to heat iron oxide. The lining must remain solid at a high temperature, be hard enough to resist abrasion, and should not conduct electricity. The engineers are comparing substances with different structures. Silicon carbide is used in some grinding wheels, while graphite can be used as an electrode.
| material | formula | melting temperature in degrees C | electrical conduction when solid | relative hardness |
|---|---|---|---|---|
| silicon carbide | SiC | 2700 | does not conduct | 9 |
| iron | Fe | 1538 | conducts | 4 |
| graphite | C | above 3500 | conducts | 1 |
| aluminium oxide | Al2O3 | 2072 | does not conduct | 9 |
(a) Use Table 1 to state the material with the highest melting temperature. [1]
(b) Name the type of structure in silicon carbide. [1]
(c) State the type of bonding in solid iron. [1]
(d) Explain why silicon carbide has a high melting temperature. [3]
(e) Use Table 1 to explain why graphite would not be selected for this furnace lining. [2]
(f) Give three properties of a giant covalent substance that are shown by silicon carbide. [3]
Answer Details
(a) The highest melting temperature listed is for graphite, which melts above \(3500\,^{\circ}\mathrm{C}\). [1]
(b) Silicon carbide has a giant covalent structure, also called a giant covalent lattice. [1]
(c) The bonding in solid iron is metallic bonding. [1]
(d) Silicon carbide has a giant lattice structure [1] containing many strong covalent bonds. [1] A large amount of energy is needed to break these bonds, [1] giving it a high melting temperature. [3]
(e) Graphite would not be suitable because it conducts electricity, [1] whereas the lining should not. It also has low hardness, with a relative hardness of 1, so it would wear away. [1] [2]
(f) Three properties of a giant covalent substance shown by silicon carbide are: high melting temperature, hardness, and no electrical conduction when solid. [3]
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