Page 155 - Science Class 08

A er 3-4 minutes, you will observe the
forma on of gas bubbles at both the
electrodes. There bubbles will displace
water in the graduated tubes.
Once, the test tubes are filled with
respec ve gases, remove them carefully so
that gases could not escape.

Test these gases one-by-one by bringing a
burning splinter of wood close to the mouth
of test tubes. Ca ons
As soon as the burning splinter is brought Posi vely charged ions are called ca ons.
close to the mouth of a test tube, it burns When atoms lose electrons they get posi vely
with pop. charged.
When the burning splinter is brought close Anions
to the mouth of another tube, the splinter
Nega vely charged atoms are called anions.
starts glowing.
When atoms gain electrons, they get nega vely
What Conclusion Do you Find? charged.
You know that hydrogen is an inflammable During electrolysis, ions with a posi ve
gas. Therefore, when the splinter is brought electrical charge move towards the cathode,

near it, it burns with pop. This shows that where they take up electrons; ions with a
the tube contains hydrogen gas. nega ve charge move towards the anode,
In the second case, the splinter starts where they give up electrons. The transfer of
electrons causes chemical changes to take place
glowing. It is because this tube contains
at each electrodes.
oxygen. You know that oxygen does not
burn, it only supports burning. Electrolysis of Copper Sulphate Solu on

Now, we can conclude that when water is In the previous ac vity, we did the electrolysis
electrolysed it decomposes into hydrogen of water and saw how it was decomposed into
and oxygen. You already know that water is hydrogen and oxygen. Now, you will see the
made of hydrogen and oxygen and hence its effect of current when it is passed through a
molecular formula in H₂O. metallic solu on.

This proves that decomposi on takes place Let us do the electrolysis of copper sulphate
when we pass electric current through solu on:
electrolytes.

ION
Aim : Electrolysis of copper sulphate
Charged atoms of an element are called ions.
solu on using carbon electrodes.
They have different number of electrons and
Method :
protons. We can categorise ions into ca ons
Arrange the apparatus as you arranged in the
and anions on the basis of the charge they
previous ac vity.
possess.

Science-8 155