Lakhmir Singh & Manjit Kaur: Chemical Effects of Electric Current- 1 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.1. Do liquids also conduct electricity? 

Liquids do conduct electricity, when they have free ions available like in case of Acids, Bases and Salts being dissolved in water.

Q.2. Name two liquids which conduct electricity and two liquids which do not conduct electricity. 

Tap water and lemon water conduct electricity, this happens because tap water. while distilled water and wine do not conduct electricity.

Q.3. Name a device which glows even when a weak electric current passes through it. 

A Light Emitting Diode (LED) glows even when a weak electric current passes through it.

Q.4. Write the full form of LED. 

Light emitting Diode (LED)

Q.5. How would you classify lemon juice- a good conductor or a poor conductor of electricity? 

Lemon juice is a good conductor of electricity. Lemon is a citrus fruit containing citric acid. Acids give H+ ions when dissolved in water, these free cations and anions make lemon juice a good conductor.

Q.6. Vinegar is a sour liquid. State whether vinegar will conduct electricity or not. 

Vinegar is a poor conductor of electricity because it does not have any free ions to carry electric charge and conduct electricity.

Q.7. What effect does an electric current produce when flowing through a conducting liquid (or conducting solution)? 

When electric current passes through a conducting liquid, it gets decomposed into ions. The conducting solution has free ions available which conduct electricity.

Q.8. When electric current is passed through acidified water, then hydrogen and oxygen are formed. What type of effect of current is illustrated by this statement? 

When electric current is passed through acidified water, it dissociates water into H+ and OH– ions. This process is called chemical effect.

Q.9. Acidified water is electrolyzed by using carbon electrodes. What is produced at:
(a) positive carbon electrode?
(b) negative carbon electrode? 

(a) Oxygen Gas is produced at positive carbon electrode.
(b) Hydrogen gas is produced as negative carbon electrode.

Q.10. Give one example of the chemical effect of electric current.

When an electric current is passed through a conducting solution, then chemical reactions take place in the solution. These chemical reactions cause chemical effects in the solution.
Example: When an electric current is passed through water, then water dissociates into hydrogen and oxygen. The chemical reaction is shown below: H₂O → H⁺ (aq) + OH^– (aq)

Q.11. What should be done to decompose water into hydrogen and oxygen? 

Electric current must be passed through water to decompose water into hydrogen and oxygen.

Q.12. Name the process in which a coating of one metal can be deposited on the surface of another metal by using current from a battery. 

Electroplating is the process in which a coating of one metal can be deposited on the surface of another metal by using current from a battery. The metal that needs to be deposited is used as the cathode while the metal on which it is deposited is used as anode. We use the salt of the cathode as the electrolyte.

Q.13. Name the metal which is usually electroplated on car parts such as bumpers and bicycle handlebars made of steel. 

Chromium is electroplated on car parts such as bumpers and bicycle handlebars made of steel.

Q.14. Which metal is electroplated on iron for making ‘cans’ used for storing food? 

Tin is electroplated on iron for making ‘cans’ used for storing food.

Q.15. Name two metal objects which have a coating of another metal.

• Chromium is electroplated on other metals.
• Gold is electroplated on other cheap metals.

Q.16. Name the most common application of the chemical effect of electric current.

The two most common examples of the chemical effect of electric current are:

• Gold Coating on cheap metals
• Electroplating of chromium metal to avoid corrosion.

Q.17. Name two metals which are usually electroplated on cheaper metals for making jewelry (or ornaments). 

Gold and silver are electroplated on cheaper metals for making jewelry or ornaments.

Q.18. Which is the polluting waste generated by electroplating factories? 

The conducting solution used in the electroplating process is the waste generated by electroplating factories.

Q.19. Give a list of five objects around you which are electroplated.

The list of five objects around you which are electroplated is:

• Kitchen utensils.
• Jewelry
• Car parts
• Cans
• Taps

Q.20. Name two metals which are purified by using the chemical effect of current (or electrolysis). 

Copper and Gold are purified by using the chemical effect of current (or electrolysis).

Q.21. Name two metals which are produced (or extracted) by using the chemical effect of electric current. 

Carbon and hydrogen are extracted by using the chemical effect of electric current.

Q.22. Name one chemical compound which is produced by using the chemical effect of electric current. 

Copper sulphate is one chemical compound which is produced by using the chemical effect of electric current.

Q.23. Name one compound which is decomposed into hydrogen and oxygen by using the chemical effect of electric current. 

Water is one compound which is decomposed into hydrogen and oxygen by using the chemical effect of electric current.

Q.24. State whether the following statements are true or false :
(a) Rainwater is a non-conductor of electricity.
(b) A piece of fresh potato does not conduct electricity at all. 

(a) False. Rainwater is a conductor of electricity because it has dissolved ions that conduct electricity.
(b) False. A piece of fresh potato conduct electricity at all because it does not have ions to conduct electricity.

Q.25. Fill in the following blanks with suitable words:
(a) Most liquids that conduct electricity are solutions of ________, ________ and ________
(b) LED glows even when a ________ electric current passes through it.
(c) The passage of an electric current through a conducting solution causes ________ effect.
(d) When electric current is passed through acidified water, then ________ and ________ are formed.
(e) The process of depositing a layer of any desired metal on another metal by means of electricity is called ________
(f) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ________ terminal of the battery.

(a) Most liquids that conduct electricity are solutions of acids, base and salts.
(b) LED glows even when a low electric current passes through it.
(c) The passage of an electric current through a conducting solution causes chemical effect.
(d) When electric current is passed through acidified water, then hydrogen and oxygen are formed.
(e) The process of depositing a layer of any desired metal on another metal by means of electricity is called electroplating.
(f) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.