8th Solved Chemical effects of electric current assignments

Q1. Do liquids also conduct electricity? Name two liquids which conduct electricity and two liquids which do not conduct electricity.

Ans: Two liquids which conduct electricity are : Lemon juice ,Vinegar, Tap water.

Two liquids which do not conduct electricity : Milk, Honey

Q2. Name a device which glows even when a weak electric current passes through it.

Ans: LED [Light Emitting Diode]

Q3.What is electrochemistry? 

Ans: Electrochemistry is defined as the branch of science that deals with chemical effect of electric current.

Q4. 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 compass is used?

Ans: (a) Heating effect              (b) Magnetic effect

Q5. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? .

Ans : No, This is because ordinary water is conductor of electricity and it will be fetal.

Q6. 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?

Ans: Chemical effect of current

Q7. State some of the characteristics of chemical changes brought about by the chemical effect of electric current.

Ans: (a) When electric current is passed through water, water dissociates into hydrogen and oxygen. Hydrogen is deposited over negative pole and oxygen is deposited over positive pole. Deposition of hydrogen and oxygen at different poles is visible in the form of bubbles.

(b) When electric current is passed through the solution of a metal salt, such as solution of copper sulphate, metal gets deposited at the negative pole, because metal is positively charged.

(c) Sometimes, the colour of solution also changes when electric current passes through it.

Q8. Name the metal which is usually electroplated on car parts such as bumpers and  bicycle handlebars made of steel.

Ans: Chromium

Q9. An iron key is to be electroplated with copper. Draw a labeled sketch of the experimental set up used for this purpose.

Ans: Iron rod made as cathode and copper rod as anode and dipped into copper sulphate electrolyte.

Credit: www.brighthubengineering.com

When current passes through copper sulphate split up into ions Cu⁺² and SO₄^-2 . Cu⁺²  move towards catode to gain electron and neutralize as cu and form layer over iron. Copper as anode losse electron and form  Cu⁺² move to electrolyte to form CuSO4

Q10. Name two metals which are usually electroplated on cheaper metals for making jewellery (or ornaments).

Ans:chromium and silver and Gold

Q11. You are required to do electroplating of copper on an iron object. Name the positive electrode (anode) and  the electrolyte you will use for this purpose.


Ans: Copper as anode and cathode as a cathode and CuSO4 as electrolyte

Q12. During electroplating the copper deposited on the plate connected to negative terminal comes from the solution. How this loss of copper from solution compensated?

Ans:  From the other plate an equal amount of copper gets dissolved in the  solution. Thus the loss of copper from the solution gets compensated and the process keeps going. This means that copper gets transferred from one plate to another.

Q13. Why does compass needle show more deflection when you test sea water, compared to ordinary water?

Ans: Sea water is more conductor compared to ordinary water as they contain lot of dissolved salt 

Q15. Describe electrolysis of water?

Ans: When electricity passes through water it splits up into H+ and O- ions. H+ move toward cathode to gain electrons to became H2 and  O- move towards anode to lose electrons to became O2

Reduction at cathode: 2 H⁺(aq) + 2e⁻ → H₂(g)

Oxidation at anode: 2 H₂O(l) → O₂(g) + 4 H⁺(aq) + 4e⁻

Q16. What happens to the needle of a magnetic compass kept nearby when electric current is switched on in a wire? Why does this happen?

Ans:  The needle of a magnetic compass shows deflection when  kept nearby a wire caring current

 as wire behave like a magnet

Q17 Iron is used in bridges and  automobile to provide strength. Which metal is electroplated on iron to protect it from corrosion?

Ans: iron is plated with nickel, chromium, tin, zinc, or cadmium.
Iron used in constructing a building is coated with a layer of zinc. This protects iron from corrosion and rusting.

Q18. We should never handle electrical appliances with wet hands or while standing on a wet floor. Why?

Ans : This is because water  conduct electric current to body and we get shock as water is good conductor.

Q19. When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into the following solution, then in which solution or solutions the compass needle shows deflection. 

Solutions are: Lemon juice, Vinegar, Tap water, Vegetable oil, milk, Honey.

Ans: Lemon juice, Vinegar, Tap water.

Q20.Why does an electric bulb glow when a current passes through it?

Ans:The bulb glows because the electricity which is a form of energy which heats a wire inside of the bulb as it passes through. This gives a glow to the wire which is magnified by the curve of a bulb.

Solution for Basic Science Publication Bharati Bhawan  [Central public School]

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VIII Science Chapter-14-Chemical Effects Of Current

CBSE NCERT 8th (VIII) Science Chapter-14-Chemical Effects Of Current
Solved Questions for formative and summative assessments [FA+SA]

Q. What is electricity?

Answer: Electricity is a phenomenon known for its effect like chemical effect, Heating effect and magnetic effect.

Q. What is the cause of electricity?

Answer: The flow of charge is the main cause of electricity.

Q. What is charge?

Answer: The fundamental properties of matter caused by gain or loss of electrons.SI unit of charge is Coulomb or C

Q. What is the charge on 1 electron?

Answer: 1.6 x 10^-19C

 Q. How many electrons present in 1 coulomb charge?

Answer: Q = n e Þ n  = (1C)/(1.6x10^-19C) = 6x10¹⁸ electrons

Q. What are the two types of electricity on the basis of charge?

Answer: the two types of electricity on the basis of charge are:

(a) Static electricity: The electricity cause by the charge at rest.

(b) Current electricity: The electricity cause by the charge when in motion

Q. What is the cause of the flow of charge?

Answer: Electric potential or potential difference is the main cause of electric charge.

Q. What do you mean by chemical effect of current?

Answer: The phenomenon of causing chemical change by passing electric current through a conduction solution is called chemical effect of current. For example: Electrolysis and Electroplating

Q. What do you mean by heating effect of current?

Answer: Whenever current flows through a conductor it causes heating of material. This effect of current is known as heating effect of current.

Q. What do you mean by magnetic effect of current?

Answer: Whenever current flows through a conductor it behaves like a magnet. This effect of current is known as magnetic effect of current.

Q. What is LED?

Answer: LED stands for Light Emitting Diode. LED glows even when a weak electric current flows through it.

Q. What precaution you should take to add LED in a circuit?

Answer: The longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.

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Chemical Effect of Electric Current VIII (8th) Physics Chapter Based Formative Assessment

Physics Chapter-Chemical Effect of Electric Current :Formative Assessment

Q.1: Fill in the blanks: Oral Questions

(i) Most liquids that conduct electricity are solutions of ---------, ---------- and ----------------

Ans: acids, bases, salt

(ii) The passage of an electric current through a solution causes ----------- effect.

Ans: Chemical

(iii) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the -------------- terminal of the battery.

Ans: negative

(iv) The process of depositing a layer of any desired metal on another metallic object, by means of electricity, is called ---------------.

Ans: electroplating.

(v)------- is an instrument to measure across any two points.

Ans: Volt meter

(vi)------------- is rate of the flow of current

Ans: Electric current

(vii) Decomposition of an electrolyte on passing electricity is called -------

Ans: Electrolysis

(viii)Chemical effect of current involve transformation of --------- energy into chemical energy.

Ans: Electrical

(ix) --------- is a source of energy give direct current.

Ans: Cell ( battery –a combination of chemical cells)

(x) --------- in an instrument used to measure flow of current

Ans: Ammeter

Short and very short type Answer Questions

Q.1. At which electrode hydrogen and oxygen gas evolved during electrolysis of water?

Ans: Hydrogen at cathode connected to negative terminal and oxygen to anode connected to positive terminal.

Q.2: When the free ends of a tester are dipped into a solution the magnetic needle shows deflection. Can you explain the reason?

Ans: Electric current flow through the tester and creates magnetic field which causes deflection of the magnetic needle of a compass.

Q.4: Name the two processes based on the principal of electrolysis?

Ans: Refining and Electroplating

Q.6: What can we do to make pure water a good conductor of electricity?

Ans: Pure water does not conduct electricity. We add electrolyte like acid, base or salt to make it conductor.

Q.8: A child staying in a coastal region tests the drinking water and also the sea water with his tester. He finds that his tester needle deflects more in case of sea water. Can you explain the reason?

Ans: Drinking water has less salt impurities than the sea water. therefore his tester needle deflects more in case of sea water.

9. How can you prove conducting properties of substances when the current is very small and bulb does not glow?

Ans: By using magnetic compass.

10. What is LED, why is it the most preferable source of electricity?

Ans: Light Emitting Diode is an electronic device that emits light even when a weak current passes through it and consumption is lesser  than Ordinary  so, is it the most preferable source of electricity .we use it  for many purposes like in traffic signals, on railway platforms as a indicators in different color

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8th physics Chemical effects of electric current Solved Questions

CBSE VIII(8th)CHEMICAL EFFECT OF ELECTRIC CURRENT

Physics Questions with their Answers

Q 1. Which of the following liquids conduct electricity and 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.

Q 2. 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.

Q 3. 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.

Q 4. 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?

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 handle, etc., made of iron?

Ans It has shiny appearance. It does not corrode easily. It resists scratches.

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 and  is protected from getting spoilt.

Q13. 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.

Q14. In the process of purification of copper metal, a thin plate of pure copper and  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.

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