EXERCISE
A. Choose the correct option:
1.When an
electric current passes through salt water , the gas liberated at the positive
electrode is →a) Chlorine
2.Which of
the following liquids conducts electricity? →a)Lemon juice
3.In which
of the following options, the liquids have been arranged in the increasing
order of conductivity ? →c)Tap water, River water, salt water
4.Iron
sheet used for making household articles are usually coated with zinc to
prevent →a)Rusting
5.Which
among the following is not an application of electroplating?
→d) Iron is coated on zinc sheet
B. State whether the following statements are true
(T) or False (F) .
1.When salt
is added to pure water ,it reduces the conductivity of water .(F)
2.Electrolyte
is a chemical substance that allows electricity to pass through it. (T)
3.Distilled
water is a good conductor of electricity.(F)
4.Base
water is a bad conductor of electricity . (F)
5.When acid
is added to pure water ,it becomes a good conductor of electric current . (T)
C. Fill in the blank using the correct words.
1.During
the electrolysis process , pure metal gets deposited at the - Cathode.
2.For
electroplating of copper on iron, the terminal of the battery that is to be
connected to the iron is – Negative .
3.The
process of coating of a metal on another metal by means of electricity is known
as – Electroplating.
4.When
electric current passes through a solution , it causes a – Chemical effect .
5.The
process of purifying a metal using an electrochemical process is known as –Electro refining.
D. Define the following terms.
1.Electrolyte:
A substance that conducts electric current in its solution or molten state is
called Electrolyte.
2.Electrplating:
The process of coating a metal with a layer of another metal using electrolysis
is called Electroplating.
3.Electrorefining
: The process of purifying a metal using electrolysis is called
Electrorefining.
4.Electrolysis:
The process of passing electricity through an electrolyte , thereby causing chemical changes is called Electrolysis.
5.Cathode
: The electrode connected to the negative terminal of the battery is known as cathode.
6.Anode:
The electrode connected to the negative
terminal of the battery is known as Anode.
E. Answer the following questions briefly.
1.Mention two application of electroplating.
ANS:-
a)Gold and
silver is coated on different ornaments
in jewellery industry .
b)Iron
parts like taps , bicycle wheel rims and handle are coated with Chromium to protect
iron from corrosion.
2. Sea water is a better conductor of
electricity than tap water .Why?
ANS:-Sea water contains a large amount of dissolved salts
in it as compared to tap water. Because of presence of ions salt solution like
sea water can conduct electricity. Therefore sea water is a better conductor of
electricity than tap water.
3. Name the gases that are obtained
during the electrolysis of water?
ANS:-The gases that are obtained during the electrolysis of
water are – Hydrogen gas at cathode and Oxygen gas at anode.
4.How do you choose an electrolyte for
electroplating a given metal on another metal ?
ANS:-In electroplating, a solution of the salt of the metal
to be coated (taken as anode) is used as
the electrolyte. For example to electroplate copper on another metal , copper
sulphate solution is used.
5.What is the advantage of dry cell
over wet cell ?
ANS:-Unlike a wet cell a dry cell can be used easily and
can be kept in any orientation .It is portable and compact compared to a wet
cell .
F. Answer the following questions in detail .
1.Explain the method of copper plating on iron nail ?
ANS:-To electroplate copper on iron nail, the materials
required are – Beaker, copper rod, iron nail, copper sulphate solution. and a
battery. Now take the solution of copper sulphate in a beaker. The connections
and setup of the experiment are as shown below:
In this setup the negative terminal of the battery is connected with the iron nail (cathode) and the positive terminal with the copper rod(anode) .Now pass electric current through the copper sulphate solution for 10-15 minutes. We will observe that a uniform brown coating forms on the iron nail because copper gets deposited on it.
2.What is electrolytic cell ? Draw its
schematic diagram.
ANS:-A electrolytic cell consisting of an electrolyte an
electrolyte and electrodes to allow free passage of electric current from an
external source .
3.Draw a schematic diagram of the set up for electrorefining copper.
ANS:-
4. What are electrodes and how do they function ?
ANS:-The two terminals dipped into the electrolyte that
make the electrical contact between the solution and the external circuit is
called Electrode.
Electrodes
are two type – cathode and anode . Generally cathode is connected to negative and anode is connected to positive
terminal of a battery. When current is passed , the ions in the electrolyte
move towards the electrodes . Cation(positive charges) moves towards the
cathode and anion (negative charge) move towards the anode.
5.Explain the working of a dry cell .
ANS:-A dry cell consist of a hollow cylindrical container
made up of zinc(negative terminal) and a carbon rod at the centre(positive
terminal). An ammonium chloride paste is used as the electrolyte. When the cell
is connected across a circuit , due to chemical reaction electron liberated at
anode (zinc) and through external circuit it reaches cathode (carbon rod).
The
chemical reaction that take palace are:
----------x---------
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