Page 178 - Chemistry ICSE Class X

164 ICSE Chemistry – 10
ƒ Procedure. An experimental set-up required for silver electroplating
is shown in Fig. 6.11.
Š Use a glass/plastic container (blackened from outside) as the
electrolytic cell.
Š Fill this container to two-third of its capacity with silver nitrate
UQNWVKQP CEKFKſGF YKVJ PKVTKE CEKF
Š Make the object to be electroplated, say a brass spoon, the cathode
(–ve electrode), and a thin plate of pure silver anode (+ve
electrode).
Š The object to be electroplated is dipped completely into the
electrolyte. When electric current is passed through the solution,
+
Ag ions move towards cathode. At the electrodes, the following
reactions take places:
–
At cathode: Ag + + e o Ag
silver ion silver atom
(from solution) (gets deposited on the
object as silver metal)
At anode: Ag o Ag + + e –
from silver anode goes into solution
–
The nitrate ion (NO ) although carries the current towards anode,
3
Fig. 6.11 An experimental set-up for it does not get oxidised at the anode. Instead, the silver (Ag) of the anode
silver electroplating gets oxidised at anode as shown above. Thus, during electroplating of
+
silver, Ag ions from the solution move to the cathode, get reduced and
get deposited on the surface of the object. Silver metal of the anode gets
+
oxidised and the Ag ions so formed go into the solution.
^ŝůǀĞƌ ŶŝƚƌĂƚĞ ; ŐEK Ϳ ƐŽůƵƟŽŶ ŝƐ ŶŽƚ
ϯ
ĚŝƌĞĐƚůLJ ƵƐĞĚ ĂƐ ƚŚĞ ĞůĞĐƚƌŽůLJƚĞ ĨŽƌ How is electroplating of nickel done
ĞůĞĐƚƌŽƉůĂƟŶŐ ŽĨ ƐŝůǀĞƌ ďĞĐĂƵƐĞ ŝƚ Certain facts regarding the electroplating of nickel are given below:
ŐŝǀĞƐ Ă ŶŽŶƵŶŝĨŽƌŵ ĚĞƉŽƐŝƚ͘
ƒ Electrolyte. Aqueous solution of nickel ammonium sulphate
.
[NiSO .(NH ) SO 6H 1? CEKFKſGF D[ CFFKPI UOCNN SWCPVKV[ QH
4
2
4
4 2
sulphuric acid (H SO ). or
2
4
Aqueous solution of nickel sulphate (NiSO CEKFKſGF YKVJ UWNRJWTKE
4
acid.
ƒ Electrodes. Cathode: The object to be electroplated with nickel
(say, an aluminium spoon)
Anode: A plate of pure nickel.
ƒ Electrolytic cell. Glass/plastic or ceramic container/vessel.
ƒ Electrode reactions. See below.
2+
+
+
ƒ Ions which carry the current. Ni (aq), NH (aq) and H (aq) ions
4
migrate towards cathode and carry the current in that direction.
2–
–
SO ions and OH ions (in minute quantity) migrate towards anode
4
and carry the current in that direction.
ƒ Ions which take part in the electrode reactions.
2+
At cathode. Ni (aq) ions get reduced to nickel and get deposited on
the object to be electroplated.
2+
2+
At anode. Nickel (Ni) gets oxidised to Ni . The Ni ions go to the
solution.
Procedure. An experimental set up for the electroplating of nickel (Ni)
on an aluminium spoon is shown in Fig. 6.12. Here, the aluminium spoon
is made cathode, and a thin strip of pure nickel is made anode. A solution
Fig. 6.12 Electroplating of nickel on of nickel ammonium sulphate [NiSO .(NH ) SO .6H O] is taken as the
aluminium spoon 4 4 2 4 2