Page 157 - Science Class 08

Let us carry out electropla ng of copper to
Aim : Electrolysis of copper sulphate using
copper electrodes.
Method:
Arrange the apparatus as shown in the
figure. You can see that we have used copper
electrodes in place of carbon electrodes.
– +
Nega ve cathode Posi ve anode
electrode electrode
Cathode Anode
(+) (–)
Cu 2+
– +
Copper Copper
deposit removed
CuSO₄ solu on
Copper electrodes should be clean and shiny.
Use a pencil to mark one electrode (+) and
the other (-). Weight each electrode with an
accurate balance before pu ng them in the
electrolyte.
Now, allow electric current to pass through
the copper sulphate solu on for half an hour.
A er half an hour stop the current. You will
observe that a layer of copper has been
deposited on an electrode. Now, wash both
electrodes with dis lled water. Dry them and
re-weigh both the electrodes separately.
What do you no ce?
You will no ce that one of the electrode has
more mass than it has earlier. While the
mass of the other electrode has decreased.
Why is it so? Actually, due to electrolysis the
cathode (-) has gained mass and is covered
with a new layer of copper. We can say that
it has been electroplated with copper. On
the other hand, the anode (+) has lost an
equal mass of copper.
It means...
Loss in mass at the anode = Gain in mass at
the cathode
Science-8
understand it properly:
Aim : Electropla ng on a metal spoon.
Method:
Take a beaker and half-fill it with copper
sulphate solu on (CuSO₄). Take a thick
copper wire and hammer it to fla er it out.
Connect it to the posi ve terminal of the
ba ery. Connect the spoon through a switch
to the nega ve terminal of the ba ery. Dip
both of them in the copper sulphate
solu on. Make sure that they do not touch
each other. Allow current to pass through the
solu on for about half and hour.
Stop the current and remove the spoon from
the beaker.
What do you observe?
You will observe that a layer of bright copper
has been deposited on the metal spoon.
CHEMICAL ANALYSIS OF ELECTROPLATING
2+
Copper sulphate contains copper ions (Cu )
2-
and sulphate ion (SO ). On passing electric
4
current through the solu on (CuSO ), copper
4
ions move towards the nega vely charged
cathode (spoon) and get converted into copper
atoms. These copper atoms get deposited on
the spoon.
At cathode (-)
2+ e-
Cu + 2 Õ Cu
2-
On the other hand, the sulphate ions (SO )
4
move towards the anode. The copper atoms of
copper rod lose an electron and convert into
2+ 2-
copper ions (Cu ). The sulphate ions (SO )
4
react with copper ions to produce copper
sulphate.
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