Question

A student added few pieces of aluminium metal to two test tubes A and B containing aqueous solutions of iron sulphate and copper sulphate. In the second part of her experiment, she added iron metal to another test tubes C and D containing aqueous solutions of aluminium sulphate and copper sulphate.

In which test tube or test tubes will she observe colour change? On the basis of this experiment, state which one is the most reactive metal and why.

Answer 1

Test tube A : `Al + FeSO_4 -> Al_2(SO_4)_3 + Fe`

Iron sulphate is a green coloured solution. However, the resultant aluminium sulphate is colourless.

Test tube B : `Al + CuSO_4 -> Al_2 (SO_4)_3 + Cu`

Copper sulphate is a blue coloured solution. However, the resultant aluminium sulphate is colourless.

Test tube C: `Fe + Al_2(SO_4)_3 -> No  reaction`

No reaction takes place here because aluminium is more reactive than iron.

Test Tube D : `Fe + CuSO_4 -> FeSO_4 + Cu`

Here, iron replaces copper and form ferrous sulphate which is a pale green coloured solution because iron is more reactive than copper.

Colour changes were observed in test tubes A, B and D.

Therefore, reactivity in decreasing order is: Al > Fe > Cu

Aluminium is the most reactive metal because it displaced both iron and copper from their compounds.