The Alkali Metals
5 marks · EasyAnswer the following about compounds of Group 1 metals and the properties of francium.
State the typical colour and solubility in water for compounds of sodium and potassium.
Give the formula and expected colour of the hydroxide formed when francium reacts with water.
Suggest what you would observe when a solution of francium hydroxide is added to universal indicator.
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.
Show answer
(a) Colourless (or white), and soluble in water · must show Colourless or white, Soluble in water
(b) Formula: FrOH; Expected colour: White or colourless · must show Formula: FrOH, Colour: White/colourless
(c) Universal indicator turns blue or purple (shows strongly alkaline solution) · must show Blue or purple colour, Alkaline solution
Common mistakes: Saying group 1 compounds are coloured; Wrong formula for francium hydroxide; Forgetting francium hydroxide is alkaline
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · States that sodium/potassium compounds are colourless or white.
A2 (a) · 1 mark · States that they are soluble in water (or 'dissolve to give colourless solutions').
B1 (b) · 1 mark · Gives correct formula: FrOH.
B2 (b) · 1 mark · States that francium hydroxide is white or colourless.
C1 (c) · 1 mark · States universal indicator turns blue or purple (shows strong alkali).
Worked solution
a) Compounds of sodium and potassium are usually colourless or white because group 1 compounds do not have coloured metal ions. They are usually soluble in water.
b) When francium reacts with water, the formula of the hydroxide formed is FrOH. Its colour will be white (solid) or give a colourless solution if dissolved in water.
c) Francium hydroxide solution is strongly alkaline. Universal indicator added to this solution would turn blue or purple.