The table below shows the electrical test results for samples used in a school science club. Each sample was connected in turn to the same cell, lamp and am...
Question 1 Report
The table below shows the electrical test results for samples used in a school science club. Each sample was connected in turn to the same cell, lamp and ammeter. The club wants to make a switch that works underwater, so it also tests whether the materials react with water.
| sample | current / A | observation with water |
|---|---|---|
| graphite | 0.42 | no visible reaction |
| diamond | 0.00 | no visible reaction |
| sodium | not tested | vigorous reaction |
(a) Use Table 1 to name the carbon form that conducts. [1]
(b) Explain why diamond gives a current of 0.00 A. [2]
(c) Describe one safety precaution needed when handling sodium and water. [2]
The table below gives boiling-point data collected during a lesson on carbon compounds. Each substance was heated in the same apparatus at normal pressure. Ethanol is a liquid fuel, whereas methane is a gas supplied to homes. The students use the data to compare small covalent molecules with giant carbon structures.
| substance | formula | boiling point / degrees C |
|---|---|---|
| methane | CH4 | -162 |
| ethanol | C2H5OH | 78 |
| graphite | C | above 3000 |
(a) Use Table 1 to name the substance with the lowest boiling point. [1]
(b) Explain why graphite has a much higher boiling point than methane. [2]
(c) Describe the forces that are overcome when methane boils. [2]
Answer Details
Electrical test
(a) Graphite conducts [1], as shown by its current of 0.42 A.
(b) In diamond, all outer electrons are used in covalent bonds [1]. There are therefore no delocalised electrons or other mobile charge carriers [1], giving a current of 0.00 A.
(c) Two suitable precautions are to wear eye protection [1] and use a small piece of sodium [1]. Sodium reacts vigorously with water. Keeping it away from naked flames or using tongs are also acceptable precautions.
Boiling-point data
(a) Methane has the lowest boiling point, 0a\(-162\ ^\circ\mathrm{C}\) [1].
(b) Graphite has a giant covalent structure [1], in which many strong covalent bonds require energy to break [1]. Methane has small molecules, so its boiling involves only weak intermolecular forces.
(c) When methane boils, weak intermolecular forces between methane molecules are overcome [1]. The covalent bonds within each methane molecule are not broken [1].
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