6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
Diamond and graphite are both forms (allotropes) of the element carbon. Diamond is very hard and does not conduct electricity. Graphite is soft and slippery and does conduct electricity.
Explain these differences in the properties of diamond and graphite in terms of their structure and bonding. (6 marks)
A student used paper chromatography to investigate the dyes in a sample of green food colouring. They drew a start line in pencil, spotted the colouring on it, and ran the chromatogram in a solvent.
One spot from the colouring travelled 3.6 cm from the start line. The solvent front travelled 4.8 cm.
(a) Calculate the Rf value of this spot. (2 marks)
(b) The green food colouring separated into two spots. What does this tell you about the food colouring? (1 mark)
(c) Explain why the start line is drawn in pencil and not in ink. (1 mark)
Magnesium chloride is an ionic compound. It contains magnesium ions (Mg2+) and chloride ions (Cl−).
(a) Deduce the formula of magnesium chloride. (1 mark)
(b) Magnesium chloride conducts electricity when molten or dissolved in water, but not when solid. Explain why. (2 marks)
The Group 1 elements (the alkali metals) become more reactive going down the group, from lithium to potassium.
Explain, in terms of electronic structure, why reactivity increases down Group 1. (3 marks)
A student melts two white solids and records the temperature at which each melts.
| Solid | Melting behaviour |
|---|---|
| A | melts sharply at 80 °C |
| B | melts gradually between 65 °C and 78 °C |
Use the data to identify which solid is pure and which is a mixture (impure). Explain your answer. (2 marks)
A mixture contains an insoluble solid (sand) suspended in water.
Name the technique used to separate the insoluble sand from the water. (1 mark)