Nov98/Paper 2/Section A/Q2
Use the information in the table to answer the following questions.
| Substance | when solid Conducts electricity | Melting point/oC | Dissolves in water |
| Sodium Chloride | No | 808 | Yes |
| Sulphur | No | 113 | No |
| Tungsten | Yes | 3377 | No |
| Wax | No | 35-50 | No |
| Aluminium | Yes | 660 | No |
(a) (i) Name two metals from the table
(ii) How can you tell from the table that the substances you have chosen in (i) are metals
(b) How can you tell from the table that wax is a mixture?
(c) (i)Name a compound from the table.
(ii) Explain the meaning of the word compound
(d) Describe hoe the arrangement and movement of particles in aluminium change as the temperature rises from 650 °C to 661 °C?
(e) Suggest how you could separate a mixture of sulphur and sodium chloride to produce a sample of each?
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Answer:
(a) (i) Tungsten and Aluminium
(ii) Metals conduct electricity in the solid state (due to the availability of free electrons) and have high melting points (strong electrostatic forces of attraction between the positive cations in a sea of negative electrons)
(b) Wax melts over a range of temperatures. Mixture are defined by the fact that they will melt over a range of temperature due to the fact that each component of the mixture has a different melting point.
(c) (i)Sodium Chloride. (It is a compound that is formed from Group I Na and Group VII Chlorine via electron transfer.)
(ii) A compound consists of 2 or more elements chemically combined with each other (Compare this to mixture. A mixture consists of 2 or more elements/mixture physically combined with each other)
(d) The melting point of Al is 660 °C. At 659 °C, it has not reached its melting point yet. Hence, it is in its solid state. The particles are closely packed together and can only vibrate about a mean position. At 660 °C, it is its melting point. The strong metallic bonds are being broken. The aluminium particles are able to move about. At 661 °C, all the particles are in continuous motion but are still closely packed together.
(e) Sulphur is hydrophobic while sodium chloride is hydrophilic. Hence, dissolve the mixture in water. Sodium chloride will form a mixture with water while sulphur will not. Pass the solution/suspension through a filter. The residue is sulphur. Evaporate the filtrate to the dryness
