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.
Sodium chloride (common salt) is an ionic compound. Solid sodium chloride does not conduct electricity, but when it is melted or dissolved in water it conducts well. Its melting point is very high (801 °C).
Explain, in terms of its structure and bonding, why sodium chloride has a high melting point and why its ability to conduct electricity changes between the solid and molten (or dissolved) states.
(6 marks)
A student uses paper chromatography to separate the coloured dyes in a food colouring. On the finished chromatogram:
(a) State why the start line (baseline) should be drawn in pencil rather than ink. (1 mark)
(b) Calculate the Rf value of this dye. Show your working. (2 marks)
(c) State what a higher Rf value tells you about how strongly a dye is attracted to the paper. (1 mark)
The elements in Group 1 of the periodic table are the alkali metals. Their reactivity increases going down the group.
(a) Explain, in terms of electronic structure, why the alkali metals become more reactive going down Group 1. (2 marks)
(b) State how the number of electrons in the outer shell of a Group 1 atom compares with the group number. (1 mark)
Chlorine is a simple molecular substance. A chlorine molecule has the formula Cl2, in which the two chlorine atoms are joined by a covalent bond.
(a) Describe what is meant by a covalent bond. (1 mark)
(b) Chlorine has a low boiling point and does not conduct electricity. Explain, in terms of its structure, why chlorine has a low boiling point. (2 marks)
Metals conduct electricity and can be bent into shape without shattering.
Explain, in terms of metallic bonding, why metals are good conductors of electricity. (2 marks)
Air is a mixture of gases, mainly nitrogen and oxygen.
State what is meant by the term mixture. (1 mark)