Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.4 Chemical Effects of Electricity Reaction offer valuable context and analysis.
WBBSE Class 8 Science Chapter 2.4 Question Answer – Chemical Effects of Electricity
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
Which of the following is non-eiectrolyte?
i) pure water square
ii) solution of glucose and water square
iii) liquid ammonia square
iv) all of tise above
Answer:
iv) all of the above
Question 2.
Which of the following is electrolyte?
i) soluton of sugar and water
ii) graphite
iii) water solution of H2 SO4
iv) water solution of glucose
Answer:
iii) water solution of H2 SO4
Question 3.
During zinc plating in anode is given-
i) iron item
ii) copper item
iii) graphite rod
iv) zinc rod square
Answer:
iv) zinc rod
Question 4.
During electrolysis of water gas produced in anode is-
i) oxygen
ii) hydrogen
iii) chlorine
iv) nitrogen
Answer:
i) oxygen
Question 5.
Plating of zinc is done to-
i) to increase beauty
ii) to prevent rusting
iii) none of the above
iv) both of the above
Answer:
iv) both of the above
Question 6.
Plating with zine is called-
i) Seradisation
ii) Galvanisation
iii) Oxidation
iv) Reduction is
Ans:
ii) Galvanisation
Question 7.
Metal used for coating on iron pipe-
i) zinc square
ii) silver
iii) nickel
iv) chromium
Answer:
iii) nickel
Question 8.
Electrolysis is used for-
i) metal extraction
ii) purification of metals
iii) electroplating
iv) All the above
Answer:
iv) All the above
State whether True or False : (1 mark for each question)
1. After a long use the handle of a bicycle lose their glaze.
2. To remove the impurities, the impure copper is purified by electroplating method.
3. In electrolysis insulated electrical wires are required for sonnections.
4. Substances like butter, ghee are not soluble in water.
5. The electrode sonnected with the positive end of battery is called cathode.
6. Disilled water mixed with salt is a bad conductor of electricity.
7. Examples of electrolytes are acid, alkali solution.
8. Elcctrolysis of fused NaCl produces sodium metal.
Answer:
1. true
2. false
3. true
4. true
5. false
6. false
7. true
8. true
Fill in the blanks : (1 mark for each question)
1. Conduction of electricity through a metai means movement of _______.
2. CuSO4 is a ______ electrolyte.
3. The compounds which do not prodace ions are calied _____.
4. The hope of _____ is taken to give the metallic coating on an object of another metal.
5. Rusting of iron occurs in contact with ____ and moisture of air.
6. Parts of a bicycle or a car or a bran tap are coated with ____.
7. To protect iron tools or utensils from rusting a thin coating of ____ is given on them.
8. Nickel plated substances are attracted by _______.
9. Impure copper is purified by _______ method.
10. Some electrolytes remain completely _______ in solution.
11. An LED can glow even at a low _______.
12. During electroplating the substance on which plating to be done is taken as _______.
Answer:
1. electrons
2. strong
3. non-clectrolytes
4. electrolysis
5. oxygen
6. chromium
7. nickel
8. magnet
9. electrolytic
10. dissociated
11. current
12. cathode
Match the following : (1 mark for each question)
a) Match the column A with column B.
| Column A | Column B |
| a) In elect: olysis of water get | i) are essential for our body |
| b) coating of zinc is given | ii) impure metal is taken as anode |
| c) Salt mixed water | iii) is a strong electrolyte |
| (d) NaCl | iv) is a bad conductor of electricity |
| e) Solution of water and glucose is | v) hydrogen and oxygen |
| f) At the time of electro- plating | vi) is a good conductor of electricity |
| g) Minerals present in drinking water | vii) in the process of electrolysis |
Answer:
a) In eletrolysis of water we get hydrogen and oxygen.
b) Coating of zinc is given in the process of electrolysis.
c) Salt mixed water is good conductor of electricity.
d) NaCl is a strong electrolyte.
e) Solution of water and glucose is a bad conductor of electricity.
f) At the time of electroplating impure metal is taken as anode.
g) Minerals present in drinking water are essential for our body.
Very Short Questions & Answers : (1 mark for each question)
Question 1.
Name a non-metal conductor.
Answer:
Graphite is a non-metal conductor.
Question 2.
Give an example of electrolyte.
Answer:
NaCl is an electrolyte.
Question 3.
Name a non-electrolyte.
Answer:
Sugar is a non-electrolyte.
Question 4.
Name a substance which is electrolyte even in solid state.
Answer:
Sodium.
Question 5.
To give a coatng of copper on a substance what is given as electrolyte solution?
Answer:
Water solution of copper’sulphate
Question 6.
Split (NH4)2 SO4 in ions.
Answer:
(NH4)2 SO4 = 2+
Short Questions & Answers : (2 marks for each question)
Question 1.
What are electrolytes? Give example.
Answer:
The compounds which are able to conduct electricity in a fused state or in a solution, are called electrolytes. Examples of electrolyies are acid or aikyle soluton, aqueous solution of a salt, fused NaCl etc.
Question 2.
What is electroplating?
Answer:
Electroplating is the process by which electric current is use to deposit one metal on the surface of another metal.
Question 3.
During electroplating which is taken as cathode and anode?
Answer:
During electroplating the substance on vhich plating is to be done is taken as cathode. The metal with which it is to be plated is taken as anode.
Question 4.
What is galvanized iron?
Answer:
Rusting of iron occurs in contact with oxygen and moisture of air. So another metal, zinc is coated over iron. It is called zinc-plated or galvanized iron.
Question 5.
How can you differ between stainless steel and nickel-coated iron?
Answer:
Nickel plated iron is attracted by a magnet very strongly, whereas stainless steel is not strongly attracted by a magnet.
Question 6.
Why wax, butter, ghee etc are non-clectrolytes?
Answer:
To be an electrolyte. a substance must produco ions in a fused state or in solution. None of these compounds produce ions. so these are not electrolytes.
Long Questions & Answers : (3 marks for each question)
Question 1.
Name the ions produced by potassium hydroxide, sulphuric acid and potassium nitrate in an aqueous solution.
Answer:
potassium hydroxide arrow K and OH
Sulphuric acid arrow H– and
Potassium nitrate arrow K– and
Question 2.
What is eiectrolysis?
Answer:
When chemical change of a substance occurs upon passage of electricity through a fused state or a solution, it is called electrolysis. Electrolysis is a redox reaction. Reduction occurs at cathode, the electrode connected to the negative terminal of the battery. Oxidation occurs at anode, the electrode connected to the positive terminal of the battery.
Question 3.
Why some acid or alkali is added with pure water in an experiment?
Answer:
Actually, the number of ions in pure water is so low, that it is not a good conductor of electrcity. So the number of ions in water must be increased. For this purpose some alkali ( NaOH or KOH ) or some acid (H2 SO4) is to be added to water. As they are strong electrolytes, the number of ions in the solution increases. Then it becomes possible to carry out electrolysis.
Question 4.
What are strong and weak electrolytes?
Answer:
Some electrolytes remain completely dissociated in solution. These are called strong electrolytes. e.g NaCl. KOH, H2 SO4, CuSO4 etc.
There are some electrolytes that remain ionised in solution only to a very small extent. These are called weak electrolytes. e.g acetic acid.
Question 5.
Give three important uses of electrolysis.
Answer:
i) Metal Extraction : Some metals are separated from their compounds by electrolysis. Some of these are sodium, potassium and calcium.
ii) Purification of metals: The metal primarily obstained from copper are is impure. To remove the impurities, the impure copper is purified by electrolytic method.
iii) Electroplating : Articles made of iron or steel are electroplated with nickel or chromium through electrolysis to prevent them from rusting.