Inorganic Chemistry
8 marks · NormalThis question is about the properties of alkali metals and halogens.
State the colour and physical state at room temperature for sodium and iodine.
Describe how you would distinguish between a sample of potassium metal and a sample of lithium metal using their observable physical properties.
Chlorine and sodium both have coloured vapours or solutions. Explain how the colour of chlorine gas compares with that of a solution containing iodine.
State the trend in colour observed down Group 1 and down Group 7 elements.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Sodium: silvery (or grey), solid. Iodine: dark grey or black, solid. · must show Sodium: solid, silvery, Iodine: solid, grey/black
(b) Potassium is softer and can be cut more easily than lithium; potassium is shinier when freshly cut. · must show Potassium: softer, Potassium: shinier when cut
(c) Chlorine gas is pale green; a solution containing iodine (iodine water) is brown. · must show Chlorine: pale green gas, Iodine solution: brown
(d) Group 1: No trend in colour (all silvery metals); Group 7: become darker in colour down the group. · must show Group 1: all silvery, Group 7: colour gets darker down group
Common mistakes: Confusing states or colours; Mixing up group trends
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Sodium: correct state and colour (solid, silvery/grey)
B2 (a) · 1 mark · Iodine: correct state and colour (solid, grey/black)
B3 (b) · 1 mark · Potassium softer than lithium or cuts more easily
B4 (b) · 1 mark · Potassium is shinier when freshly cut
B5 (c) · 1 mark · Chlorine gas is pale green
B6 (c) · 1 mark · Iodine solution is brown
B7 (d) · 1 mark · Group 1: all silvery, no colour trend
B8 (d) · 1 mark · Group 7: colour darkens down the group
Worked solution
a. Sodium is a silvery, solid metal at room temperature. Iodine is a dark grey or black solid at room temperature.
b. Potassium is softer than lithium; it can be cut more easily and is more shiny inside when freshly cut.
c. Chlorine gas is pale green, while a solution containing iodine is brown.
d. Group 1 metals are all silvery with no colour change down the group; Group 7 elements become darker in colour as you go down the group (from pale yellow-green for chlorine to dark grey/black for iodine).