Q. 25.0( 1 Vote )

Observing the action of Zn, Fe, Cu and Al metals on the following salt solutions :
(a) ZnSO4(aq.)
(b) FeSO4(aq.)
(c) CuSO4(aq.)
(d) Al2(SO4)3(aq.)
(ii) Arranging Zn, Fe, Cu and Al (metals) in the decreasing order of reactivity based on the above result.

Answer :

Let us study the relative reactivity of metals using Salt Solution with the help of experiment shown here. 

MATERIALS REQUIRED

Test tubes, test stand, metals-Zn granules, Fe filings, Cu turnings, Al foil and aqueous solutions of zinc sulphate, ferrous sulphate, copper sulphate and aluminium sulphate.

THEORY

In a displacement reaction, an ion or an atom in a compound is replaced by an ion or an atom of zinc sulphate element. It may be denoted as

X + YZ → XZ + Y

The displacement reactions are based on the reactivity series, where a more reactive metal displaces a less reactive metal from its salt solution.

For three different metals A, B, C if metal A replaces metal B from its aqueous solution then metal A is more reactive than metal B.

It metal C displaces metal B from its salt solution, but metal A displaces metal C from its salt solution it follows that the increasing order of reactivity is :

B < C < A

When pieces of Zn are dipped in copper sulphate solution, the blue colour of copper sulphate starts fading and reddish-brown particles of copper settle at the bottom. This occurs because of the following reaction :


Some other examples of displacement reactions are as follows:



Colour of solutions and metals


PROCEDURE

1. Take four test tubes and label them as ZnSO4, FeSO4 and Al2(SO4)3.

2. Pour an equal amount of their aqueous solution into the respective test tubes.

3. Add a small strip of Al foil to each of the test tubes.

4. Observe the change and record your observations.

5. Repeat a similar procedure using :

(a) Cu turnings with ZnSO4, FeSO4, CuSO4 and Al2(SO4)3 solutions

(b) Fe filings with ZnSO4, FeSO4, CuSO4 and Al2(SO4)3 solutions

(c) Zn granules with ZnSO4, FeSO4, CuSO4 and Al2(SO4)3 solutions

Record your observations in the following table :

OBSERVATIONS




RESULT

1. Al is able to displace Fe, Cu and Zn from their salt solutions, therefore Al is most reactive.

2. Cu is unable to displace any metal among Al, Fe and Zn from their salt solutions, therefore Cu is least reactive.

3. Fe is unable to displace Zn from its salt solution, whereas Zn is able to displace Fe from its salt solution, therefore Zn is more reactive than Fe.

4. The decreasing order of reactivity for these metals follow the order :

Al > Zn > Fe > Cu

PRECAUTIONS

1. Handle the chemicals carefully.

2. Clean each metal with sandpaper.

3. Observe the changes carefully as few reactions may occur slowly.

4. Do not taste the chemicals.

5. Wash your hands properly after the experiment.

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