Predicting the properties of francium
5 marks · HardFrancium is a Group 1 alkali metal that has never been seen directly. Chemists use trends to predict its properties.
State the expected physical appearance of francium when freshly cut.
Explain why francium would be stored under oil if it could be collected in the laboratory.
Describe and explain what you would expect to happen if francium was dropped into water.
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(a) Shiny, silvery metal (accept: shiny, metallic, silvery-white)
(b) Francium would react very rapidly with air and moisture, forming oxides and tarnishing instantly, so it must be stored under oil to prevent reaction with air or water vapour.
(c) Francium would react extremely violently with water, more so than caesium, producing hydrogen gas and francium hydroxide, with much heat, and possibly an explosion; this is because it is the most reactive alkali metal.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States appearance: shiny/silvery/metallic when freshly cut.
M1 (b) · 1 mark · Explains reacting/tarnishing instantly with air/moisture.
A1 (b) · 1 mark · Mentions storage under oil prevents this reaction/tarnishing.
M2 (c) · 1 mark · Describes violent or explosive reaction with water, producing hydrogen and francium hydroxide.
A2 (c) · 1 mark · Correctly explains this is due to francium being the most reactive alkali metal (reason linked to trend and position in group).
Worked solution
a) Francium would be a shiny, silvery metal when freshly cut.
b) Francium would tarnish/react instantly with air or moisture, so it would be stored under oil to prevent this reaction.
c) Francium would react extremely violently when dropped in water, producing hydrogen gas and francium hydroxide, and likely enough heat to cause an explosion, because it is the most reactive alkali metal.