Solved Questions - Chemical effects of current - Class 8 PDF Download

 Page 1


JSUNIL TUTORIAL ,SAMASTIPUR 
 
CLASS VIII   Chemical effects of electric current solved Questions  Page 1 
 
Q1. Which of the following liquids conduct electricity & which do not conduct 
electricity? 
Lemon juice, Milk, Vinegar, Salt solution, Distilled water, Honey, Sea water, Rain 
water. 
Ans: Conducting: Lemon juice, Vinegar, Salt solution, sea water, Rain water Non 
Conducting: Milk, Distilled water, Honey. 
Q2. What is advantage of using LED over bulb in testing the electrical 
conductivity of liquids? 
Ans: When electric current flows through a bulb then due to heating effect of current, 
the filament of the bulb gets heated up to a high temperature & it starts glowing. Now 
for a liquids having low electrical conductivity, the current flowing through the circuit is  
very weak due to which the filament does not get heated sufficiently & hence the bulb 
does not glow. Therefore LED is used in place of bulb because LED glows even 
when weak electric current flows in the circuit. 
Q3. Which effect of electric current is utilized for detecting the flow of current  
through a solution: 
a)  When a torch bulb is used? b) When a magnetic compass is used? 
Ans: a) Heating effect            b) Magnetic effect. 
Q4. Distilled water does not conduct electricity. What substances can be added 
to distilled water in small amounts to make it a good conductor of electricity? 
Ans: Salt, acid & base. 
Q5. In case of a fire, before the fireman uses the water hoses to throw water to 
douse fire, they shut off the electricity supply for the area. Explain why this is 
done? 
Ans: To prevent electrocution of fireman because ordinary water is conductor of 
electricity. 
Q6. When the free ends of a conductivity tester (made by using a battery 
connected to a wire wound around a compass) are dipped into a solution, the 
magnetic needle shows deflection. Can you give the reason of this deflection? 
Page 2


JSUNIL TUTORIAL ,SAMASTIPUR 
 
CLASS VIII   Chemical effects of electric current solved Questions  Page 1 
 
Q1. Which of the following liquids conduct electricity & which do not conduct 
electricity? 
Lemon juice, Milk, Vinegar, Salt solution, Distilled water, Honey, Sea water, Rain 
water. 
Ans: Conducting: Lemon juice, Vinegar, Salt solution, sea water, Rain water Non 
Conducting: Milk, Distilled water, Honey. 
Q2. What is advantage of using LED over bulb in testing the electrical 
conductivity of liquids? 
Ans: When electric current flows through a bulb then due to heating effect of current, 
the filament of the bulb gets heated up to a high temperature & it starts glowing. Now 
for a liquids having low electrical conductivity, the current flowing through the circuit is  
very weak due to which the filament does not get heated sufficiently & hence the bulb 
does not glow. Therefore LED is used in place of bulb because LED glows even 
when weak electric current flows in the circuit. 
Q3. Which effect of electric current is utilized for detecting the flow of current  
through a solution: 
a)  When a torch bulb is used? b) When a magnetic compass is used? 
Ans: a) Heating effect            b) Magnetic effect. 
Q4. Distilled water does not conduct electricity. What substances can be added 
to distilled water in small amounts to make it a good conductor of electricity? 
Ans: Salt, acid & base. 
Q5. In case of a fire, before the fireman uses the water hoses to throw water to 
douse fire, they shut off the electricity supply for the area. Explain why this is 
done? 
Ans: To prevent electrocution of fireman because ordinary water is conductor of 
electricity. 
Q6. When the free ends of a conductivity tester (made by using a battery 
connected to a wire wound around a compass) are dipped into a solution, the 
magnetic needle shows deflection. Can you give the reason of this deflection? 
JSUNIL TUTORIAL ,SAMASTIPUR 
 
CLASS VIII   Chemical effects of electric current solved Questions  Page 2 
 
Ans: Electric current flowing through the wire produces a magnetic field around it.  
And this magnetic field of electric current acts on the magnetic needle of compass & 
deflects it. 
Q7. What effects does an electric current produce when flowing through a 
conducting solution? 
Ans: When an electric current flows through the conducting solution, it causes a 
chemical reaction (or chemical change). These chemical reactions may produce 
following effects: 
i) Bubbles of gas/es may be formed on the electrodes. 
 ii) Deposits of metals may form on electrodes.  
iii) Change in colour of solution may occur. 
Q8. When electric current is passed through acidified water then what is 
produced at  
a) Positive carbon electrode (anode)?        b) Negative carbon electrode 
(cathode)? 
Ans: a) oxygen gas b) hydrogen gas. 
Q9. Which effect of electric current is utilized when a thin layer of chromium 
metal is deposited on an iron tap? What is this process known as? 
Ans: Chemical effect of current is utilized. The process is known as electroplating. 
Q10. What is meant by electroplating? What is the purpose of electroplating? 
Ans: The process of depositing a layer of any desired metal on another material, by 
means of electricity, is called electroplating. Electroplating is done  
i)  for protection against corrosion (or rusting). 
ii) for decorative purposes. 
Q11. Which properties of chromium metal make it suitable for electroplating it 
on car bumpers, bath taps & bicycle hand bars, etc., made of iron? 
Ans It has shiny appearance. It does not corrode easily. It resists scratches. 
Page 3


JSUNIL TUTORIAL ,SAMASTIPUR 
 
CLASS VIII   Chemical effects of electric current solved Questions  Page 1 
 
Q1. Which of the following liquids conduct electricity & which do not conduct 
electricity? 
Lemon juice, Milk, Vinegar, Salt solution, Distilled water, Honey, Sea water, Rain 
water. 
Ans: Conducting: Lemon juice, Vinegar, Salt solution, sea water, Rain water Non 
Conducting: Milk, Distilled water, Honey. 
Q2. What is advantage of using LED over bulb in testing the electrical 
conductivity of liquids? 
Ans: When electric current flows through a bulb then due to heating effect of current, 
the filament of the bulb gets heated up to a high temperature & it starts glowing. Now 
for a liquids having low electrical conductivity, the current flowing through the circuit is  
very weak due to which the filament does not get heated sufficiently & hence the bulb 
does not glow. Therefore LED is used in place of bulb because LED glows even 
when weak electric current flows in the circuit. 
Q3. Which effect of electric current is utilized for detecting the flow of current  
through a solution: 
a)  When a torch bulb is used? b) When a magnetic compass is used? 
Ans: a) Heating effect            b) Magnetic effect. 
Q4. Distilled water does not conduct electricity. What substances can be added 
to distilled water in small amounts to make it a good conductor of electricity? 
Ans: Salt, acid & base. 
Q5. In case of a fire, before the fireman uses the water hoses to throw water to 
douse fire, they shut off the electricity supply for the area. Explain why this is 
done? 
Ans: To prevent electrocution of fireman because ordinary water is conductor of 
electricity. 
Q6. When the free ends of a conductivity tester (made by using a battery 
connected to a wire wound around a compass) are dipped into a solution, the 
magnetic needle shows deflection. Can you give the reason of this deflection? 
JSUNIL TUTORIAL ,SAMASTIPUR 
 
CLASS VIII   Chemical effects of electric current solved Questions  Page 2 
 
Ans: Electric current flowing through the wire produces a magnetic field around it.  
And this magnetic field of electric current acts on the magnetic needle of compass & 
deflects it. 
Q7. What effects does an electric current produce when flowing through a 
conducting solution? 
Ans: When an electric current flows through the conducting solution, it causes a 
chemical reaction (or chemical change). These chemical reactions may produce 
following effects: 
i) Bubbles of gas/es may be formed on the electrodes. 
 ii) Deposits of metals may form on electrodes.  
iii) Change in colour of solution may occur. 
Q8. When electric current is passed through acidified water then what is 
produced at  
a) Positive carbon electrode (anode)?        b) Negative carbon electrode 
(cathode)? 
Ans: a) oxygen gas b) hydrogen gas. 
Q9. Which effect of electric current is utilized when a thin layer of chromium 
metal is deposited on an iron tap? What is this process known as? 
Ans: Chemical effect of current is utilized. The process is known as electroplating. 
Q10. What is meant by electroplating? What is the purpose of electroplating? 
Ans: The process of depositing a layer of any desired metal on another material, by 
means of electricity, is called electroplating. Electroplating is done  
i)  for protection against corrosion (or rusting). 
ii) for decorative purposes. 
Q11. Which properties of chromium metal make it suitable for electroplating it 
on car bumpers, bath taps & bicycle hand bars, etc., made of iron? 
Ans It has shiny appearance. It does not corrode easily. It resists scratches. 
JSUNIL TUTORIAL ,SAMASTIPUR 
 
CLASS VIII   Chemical effects of electric current solved Questions  Page 3 
 
Q12. Which metal is electroplated on iron for making ‘cans’ used for storing 
food & Why? 
Ans: Tin. Tin metal has shiny appearance, it does not corrode & it is non poisonous. 
Tin is less reactive than iron. Due to tin plating over the surface of iron, the food does 
not come in contact with iron & is protected from getting spoilt. 
Q13. For electroplating copper on an iron object, which terminal of the 
battery is connected to the iron objects? 
Ans: Negative terminal of the battery 
Q14. In the process of purification of copper metal, a thin plate of pure copper 
& a thick rod of impure copper are used as electrodes & a metal salt solution is 
used as an electrolyte: 
a) Which electrode is connected to the positive terminal of the battery? 
b) Which electrode is connected to the negative terminal of the battery? 
c)  Which metal salt solution is taken as electrolyte? 
Ans: a) Thick rod of impure copper.     b) Thin rod of pure copper. c) Copper sulphate 
solution. 
Q15. Write down the important points which should be remembered while 
electroplating? 
Ans: i)  The metal on which electroplating is to be done should be cathode i.e., the 
negative electrode. 
ii) The metal to be deposited should be anode i.e., the positive electrode. 
iii) A water soluble salt of the ‘metal to be deposited’ is taken as the electrolyte.  
Q16. On what factors the chemical effect produced by an electric current 
depends? 
Ans: The chemical effect produced by an electric current depends on the nature of 
conducting solution (through which it is passed), & on the nature of electrodes used 
for passing the electric current