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.

The student will observe a colour change in test tubes A and C. In test tube A, aluminium will displace iron from iron sulphate solution because aluminium is more reactive than iron. In test tube C, iron will displace aluminium from aluminium sulphate solution because iron is more reactive than aluminium but less reactive than aluminium in this case as aluminium sulphate is a salt of weak acid and iron is more reactive than aluminium in case of weak acid salts. However, in test tube B, aluminium cannot displace copper from copper sulphate solution because aluminium is less reactive than copper. Similarly, in test tube D, iron cannot displace copper from copper sulphate solution because iron is less reactive than copper. Therefore, aluminium is the most reactive metal among the three.