Question

100 ml of a saturated copper sulphate solution was taken in a beaker. A small amount of iron filings was added to the beaker and left undisturbed overnight. The mixture was then filtered to obtain the residue. The colour of the residue was found to be*

(a) greenish blue

(b) faint green

(c) steel grey

(d) reddish brown.​

Answer 1

Answer:-

The colour of the solution becomes (a) greenish blue .

This is because , copper is a low reactive metal other than Iron. Hence, when iron is added to copper sulphate , Iron displaces carbon and reacts with sulphate ion to give Iron sulphate.

Equation:

CuSO4(aq) + Fe(s) → FeSO4 + Cu

And , This is an example for Displacement reaction.

Additional Information:

Displacement Reaction:

• When a highly reactive metal displaces less reactive metal from its aqueous salt solution , this chemical reaction is called Chemical displacement reaction.

Another example for this is :

When a strip of zinc is added to CuSO4 , zinc replaces copper and forms ZnSO4 (Zinc Sulphate)

Equation:

CuSO4(aq) + Zn(s) = ZnSO4 + Cu

List of metals in the order of decreasing chemical reactivities :

K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag

(F > Cl > Br > I)

Answer 2

The colour of the residue was found to be (d) reddish-brown.

• The mixture of copper sulphate reacts with iron fillings. The reaction is a single displacement reaction where iron reacts with sulphate ions to form a compound. Copper ions get reduced to form copper.
• The residue obtained is copper.
• The mentioned chemical reaction is as follows - CuSO4 (aq) + Fe (s) --> FeSO4 (aq) + Cu (s)
• In the reaction, CuSO4 is copper sulphate, Fe is iron, FeSO4 is ferrous sulphate and Cu is copper.

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