AQA A Level chemistry Group 2

A laboratory technician discovered four badly−labelled bottles, each containing one pure white solid. Each bottle contained a compound of a different Group 2 metal (magnesium, calcium, strontium and barium).
Some tests were carried out on the solids or, if the compound was soluble, on the aqueous solution. The results are given in the table.

Test
Compound 1
Compound 2
Compound 3
Compound 4
Added to water
Dissolves
Insoluble
Dissolves
Dissolves
Solution or solid added to HCl(aq)
Solution
remains colourless
Gives off carbon dioxide gas and a colourless solution forms
Solution
remains colourless
Solution
remains colourless and heat released
Solution or solid added to NaOH(aq)
Solution gives a white
precipitate
Solid remains insoluble
Solution gives a slight white precipitate
Solution has no visible change
Solution or solid added to H2SO4(aq)
Solution has no visible change
Gives off carbon dioxide gas and a white solid remains
Solution slowly forms a slight white
precipitate
Solution forms
a white precipitate

(a) One of the bottles has a very faint label that could be read as ‘Magnesium Sulfate’.
Use the information in the table to deduce which one of the four compounds is magnesium sulfate and explain your answer.

Does anyone know which paper this question is from please? Or how to work out the answer?

Reply 1

kaiakrion

Dunno where the question is from but i worked out that it's compound 1 for the following reasons:

1. MgSO4 is not insoluble in water, and doesn't give off CO2 so that eliminates compound 2
2. MgSO4 does react with NaOH to give a white precipitate of Mg(OH)2 so that eliminates compound 4
3. MgSO4 shows no visible reaction/change when added to H2SO4 because the SO4 2- ion is already present so that eliminates Compound 3

This leaves us with compound 1, and as a check, when the MgSO4 solution is added to dilute HCl, it does remain colourless so it adds up. TBH point 3 is all you need to prove it. Hope this helps!