Chemical Effects of Electric Current – Short Answer Type Questions
CBSE Class 8 Science – Chapter Wise Study Materials Based on NCERT
Chapter 14: Chemical Effects of Electric Current – Short Answer Type Questions
Suitable for:
Annual Examination • Periodic Tests • Class Tests • Pre-Board / School Level Board Exam Pattern
These Short Questions with Answers are designed strictly as per the NCERT syllabus, making them ideal for CBSE Class 8 board exams standard.
This page contains a topic-wise set of 50 Short Answer Type Questions from
Chapter 14: Chemical Effects of Electric Current with clear, easy-to-understand answers
to strengthen concepts and support exam-focused revision.
Short Answer Type Questions – Chapter 14
A. Conductors, Insulators and Conducting Liquids
Q1.What is a conductor? Give two examples.
A conductor is a substance that allows electric current to pass through it easily because it has free electrons or ions.
Examples: copper and aluminium.
Q2.Define an insulator with two examples.
An insulator is a substance that does not allow electric current to pass through it easily.
Examples: plastic and rubber. They have no free charge carriers and are used for covering wires and plugs.
Q3.What is meant by a conducting liquid?
A conducting liquid is a liquid that allows electric current to pass through it.
It usually contains ions (charged particles) which move when a potential difference is applied and conduct electricity.
Q4.Why does a solution of common salt in water conduct electricity but distilled water does not?
Distilled water does not contain dissolved salts and hence has almost no ions, so it does not conduct electricity.
When common salt is added, it dissolves and produces ions, making the solution a good conductor of electricity.
Q5.How can you show that tap water is a better conductor than distilled water?
Set up an electric circuit with a bulb or LED and place two electrodes in a beaker of distilled water.
The bulb does not glow. Replace distilled water with tap water; the bulb/LED glows faintly.
This shows that tap water is a better conductor because it contains dissolved salts and minerals (ions).
Q6.Classify: lemon juice, kerosene, sugar solution, vinegar – into conductors and insulators.
- Conductors: Lemon juice and vinegar (they contain acids and ions).
- Poor conductors/insulators: Kerosene and sugar solution in small concentration (almost no ions).
Q7.Why is the human body considered a conductor of electricity?
The human body contains water with dissolved salts and minerals, which provide ions.
These ions allow electric current to pass through the body, so it behaves as a conductor of electricity.
Q8.Why should we be careful while working with electricity near water?
Water, especially tap water, is a conductor due to dissolved salts.
If we touch electrical appliances with wet hands or stand on a wet floor, current can pass through our body and cause an electric shock, so we must be very careful.
B. Testing Conductivity – LED, Bulb and Magnetic Effect
Q9.Describe a simple circuit to test whether a liquid conducts electricity.
Connect a battery, a switch and a bulb/LED in series.
Attach two conducting electrodes to the free ends of the wires and dip them in the liquid.
If the bulb/LED glows when the switch is turned on, the liquid conducts electricity; otherwise it does not (or conducts very weakly).
Q10.Why may an ordinary bulb sometimes fail to show conduction in a liquid even if the liquid is a weak conductor?
An ordinary filament bulb requires a comparatively larger current to glow.
If the liquid allows only a very small current, it may not be sufficient to heat the filament,
so the bulb will not glow even though some current is passing through the liquid.
Q11.How does an LED help in detecting weak currents through a liquid?
An LED (Light Emitting Diode) is very sensitive and can glow even with a small current.
When used in the testing circuit, it can detect weak currents in liquids that are not strong enough to light a normal bulb,
thus helping us identify weak conductors among liquids.
Q12.How can the magnetic effect of current be used to test conduction in a liquid?
In the circuit, a coil of wire is placed near a compass needle.
The circuit is completed with two electrodes dipped in the liquid.
If the liquid conducts, current flows through the coil, producing a magnetic field and causing the compass needle to deflect,
showing that the liquid is conducting electricity.
Q13.What conclusion can you draw if neither the bulb glows nor the compass needle deflects when a liquid is used in the circuit?
If neither the bulb glows nor the compass needle deflects, it shows that the liquid does not allow sufficient current to pass through it.
It is therefore a poor conductor or almost an insulator at the given conditions.
Q14.Why is it important to clean the electrodes before using them in a conductivity experiment?
Electrodes may have oxide layers, grease or dirt on their surface, which can reduce the contact with the solution and affect conduction.
Cleaning removes these layers so that the true conducting property of the liquid can be tested accurately.
C. Chemical Effects of Electric Current – Basic Ideas
Q15.What is meant by the chemical effect of electric current?
When electric current is passed through certain conducting liquids, they undergo chemical changes such as gas formation,
colour change or deposition of metals. These changes produced due to electric current are called the chemical effects of electric current.
Q16.Mention any three changes that may occur in a solution due to the chemical effect of current.
The three changes are:
- Formation of gas bubbles at one or both electrodes.
- Change in colour of the solution.
- Deposition of a metal or change in mass of the electrodes.
Q17.What is an electrolyte? Give one example.
An electrolyte is a conducting liquid or solution through which electric current can pass because it contains ions.
Example: Copper sulphate solution or sodium chloride (salt) solution in water is an electrolyte.
Q18.What are electrodes? Which materials are commonly used as electrodes?
Electrodes are conducting rods or plates dipped in an electrolyte and connected to a battery.
They allow current to enter and leave the solution. Metals like copper, zinc and iron, or graphite (carbon rods),
are commonly used as electrodes in school experiments and industries.
Q19.Define anode and cathode in an electrolytic cell.
In an electrolytic cell:
- Anode is the positive electrode connected to the positive terminal of the battery.
- Cathode is the negative electrode connected to the negative terminal of the battery.
Q20.Why do some liquids show chemical effects when current is passed through them while others do not?
Liquids that contain ions, such as solutions of acids, bases and salts, conduct electricity and undergo chemical changes (chemical effects)
when current passes through them. Liquids like pure water, oil or kerosene have almost no ions and therefore do not show noticeable chemical effects of current.
Q21.How can passing an electric current through a solution lead to the formation of new substances?
When current passes through an electrolyte, ions move towards electrodes and may gain or lose electrons there.
This can break down the compound into simpler substances or form new products like gases or metals,
thereby changing the chemical composition of the solution and producing new substances.
D. Copper Sulphate Experiment and Related Concepts
Q22.Describe the basic setup of the copper sulphate experiment given in NCERT.
Take copper sulphate solution in a beaker and dip two clean copper plates as electrodes.
Connect one plate to the positive terminal (anode) and the other to the negative terminal (cathode) of a battery.
Allow current to pass for some time and observe changes at the electrodes and in the solution.
Q23.What changes are observed at the cathode in the copper sulphate experiment?
At the cathode, a reddish-brown layer of copper metal is deposited.
This shows that copper ions from the solution gain electrons at the cathode and get converted into copper metal,
which sticks to the cathode surface, making it thicker and heavier.
Q24.What happens to the anode in the copper sulphate experiment and why?
The copper anode gradually becomes thinner because copper atoms from the anode lose electrons and go into the solution as copper ions.
Thus, some copper from the anode dissolves into the solution to replace the ions deposited at the cathode, maintaining the concentration of the solution.
Q25.Why does the colour of copper sulphate solution remain almost unchanged in this experiment?
Copper ions from the solution are deposited on the cathode, but at the same time, copper atoms from the anode dissolve to form new copper ions.
The loss and gain of copper ions balance each other, so the overall concentration of Cu2+ ions, and hence the blue colour of the solution, remains almost unchanged for some time.
Q26.How does the copper sulphate experiment prove that electric current can cause chemical changes?
In this experiment, current causes a transfer of copper from the anode to the cathode and changes the masses of electrodes.
These changes involve breaking and forming of chemical bonds and the movement of ions, which clearly shows that electric current has produced chemical changes in the system (chemical effect of electric current).
Q27.What will happen if iron plates are used as electrodes in copper sulphate solution instead of copper plates?
If iron plates are used, iron may react with copper sulphate solution.
A displacement reaction can occur in which iron displaces copper from copper sulphate, leading to the formation of iron sulphate and deposition of copper on iron.
The solution’s colour and composition will change due to both chemical and electrolytic effects.
E. Electrolysis and Role of Ions
Q28.What is electrolysis? Explain in simple words.
Electrolysis is the process in which an electric current is passed through a conducting liquid (electrolyte)
and causes it to break down into simpler substances or its components.
It is a chemical decomposition brought about by electricity, as in the breakdown of copper sulphate solution into copper and other ions at the electrodes.
Q29.What are ions? How do they help in conduction of electricity in liquids?
Ions are charged particles formed when atoms or molecules gain or lose electrons.
Positive ions are called cations and negative ions are called anions.
In liquids, these ions move freely and carry electric charge from one electrode to the other, thus allowing current to flow through the liquid.
Q30.Why do solutions of acids, bases and salts conduct electricity?
Solutions of acids, bases and salts contain ions when dissolved in water.
Acids provide H+ ions, bases provide OH− ions and salts provide both positive and negative ions.
These ions move under the influence of electric field and make the solution conductive, allowing electric current to pass.
Q31.Explain what happens to positive and negative ions during electrolysis.
During electrolysis, positive ions (cations) move towards the cathode, where they gain electrons and may be converted into neutral atoms or molecules.
Negative ions (anions) move towards the anode, where they lose electrons and may form neutral substances or gases.
These reactions cause chemical changes at the electrodes and in the solution.
Q32.Why is it dangerous to insert metal objects into an electric socket when you are in contact with water?
Metal objects are good conductors and water on our body increases conductivity due to ions.
Inserting a metal object into a live socket can allow a large current to pass through our body and water path to the earth,
causing a serious or even fatal electric shock. Therefore, it is extremely dangerous and should never be done.
F. Electroplating – Principle and Setup
Q33.Define electroplating and mention its main purpose.
Electroplating is the process of depositing a thin layer of one metal over the surface of another metal object by passing electric current through an electrolyte.
Its main purposes are to protect the object from corrosion and to improve its appearance by giving it a shiny or decorative finish.
Q34.In an electroplating setup, which electrode is the object to be plated and how is it connected?
The object to be plated is always taken as the cathode (negative electrode).
It is connected to the negative terminal of the battery so that positive metal ions from the solution are attracted to it and deposited as a thin layer of metal on its surface.
Q35.Which electrode provides the metal in electroplating and how is it connected?
The electrode made of the metal that is to be deposited acts as the anode (positive electrode).
It is connected to the positive terminal of the battery.
Metal atoms from this anode lose electrons, become ions, go into the solution and later get deposited on the cathode (object to be plated).
Q36.What type of solution is used as electrolyte during electroplating? Give an example.
The electrolyte used for electroplating is a solution of a salt of the metal to be deposited.
For example, for copper plating, a solution of copper sulphate is used; for silver plating, a solution of silver nitrate or other silver salt is used.
These solutions provide metal ions for deposition on the cathode.
Q37.Explain why the object to be electroplated must be thoroughly cleaned before electroplating.
If dirt, grease, rust or oxide layers remain on the object, the deposited metal layer will not stick properly and may peel off.
Cleaning removes these impurities and exposes a smooth metal surface, so that the thin layer of plating metal forms a strong, even coating on the object.
Q38.Describe the electroplating of an iron key with copper.
To electroplate an iron key with copper:
- Clean the iron key thoroughly and connect it to the negative terminal of a battery (cathode).
- Use a copper plate as the anode and connect it to the positive terminal.
- Take copper sulphate solution as the electrolyte and dip both electrodes in it.
- When current is passed, copper ions from the solution deposit on the iron key, forming a thin copper layer on its surface.
Q39.What changes occur at the anode and cathode during electroplating of copper on an iron object?
At the anode (copper strip), copper atoms lose electrons and go into the solution as Cu2+ ions, making the anode thinner.
At the cathode (iron object), Cu2+ ions from the solution gain electrons and get deposited as copper metal,
forming a thin layer on the iron object and increasing its mass slightly.
Q40.State the general rule for choosing the cathode, anode and electrolyte for electroplating.
The general rule is:
- The object to be plated is the cathode (negative electrode).
- The metal that is to be deposited is the anode (positive electrode).
- The electrolyte is a solution of a salt of that metal.
G. Uses and Advantages of Electroplating
Q41.How does electroplating protect metal objects from corrosion?
Electroplating covers the surface of a reactive metal (like iron) with a thin layer of a less reactive metal (like tin, chromium or zinc).
The coating metal does not corrode easily and prevents air and moisture from reaching the underlying metal, thus protecting it from rust and corrosion for a longer time.
Q42.Why is chromium-plating done on car and bicycle parts?
Chromium is shiny and resistant to corrosion.
By electroplating a thin layer of chromium on iron or steel parts of cars and bicycles,
they become more attractive and durable while using only a small amount of expensive chromium metal, making it economical and protective at the same time.
Q43.Give two examples from daily life where electroplating is used.
Two examples are:
- Electroplating of artificial jewellery with gold or silver to give it a rich, attractive appearance.
- Electroplating of iron cans with tin, so that food stored inside does not react with iron and remains safe.
Q44.How does electroplating help in saving the amount of costly metals?
In electroplating, only a very thin layer of costly metal is deposited on the surface of a cheaper base metal.
The inner part of the object is made of inexpensive metal, while the outside looks and behaves like the expensive metal.
This gives the desired properties and appearance at a much lower cost, saving a large amount of costly metal.
Q45.Why is electroplating widely used in the industry?
Electroplating is widely used because it:
- Protects metal objects from corrosion and wear.
- Improves appearance by giving a shiny, decorative finish.
- Provides special surface properties (hardness, smoothness) without using expensive metal for the entire object.
- Is economical and can be controlled to produce very uniform coatings.
H. Safety, Precautions and Miscellaneous Concepts
Q46.Why should only small cells or batteries be used in school experiments on chemical effects of electric current?
Small cells or batteries provide a limited and safe amount of current and voltage.
Using mains electricity for such experiments is dangerous because it can cause electric shocks, burns or fires if there is any mistake in the circuit or if liquids spill.
Therefore, only low-voltage batteries are used in school laboratories for safety reasons.
Q47.State two precautions to be taken while performing experiments involving electric current and liquids.
Two precautions are:
- Do not touch the circuit or electrodes when the current is switched on, especially with wet hands.
- Use low-voltage batteries and avoid spilling liquids on the battery or other electrical connections.
Q48.What kind of change is the electroplating of an object – physical or chemical? Explain.
Electroplating is a chemical change because a new layer of metal is chemically formed and deposited on the surface of the object.
This change involves the movement of ions and electron transfer at electrodes and generally cannot be reversed easily by simple physical methods,
so it is considered a chemical change rather than just a physical one.
Q49.Why should we not use acids and other strong chemicals carelessly during experiments on chemical effects?
Acids and strong chemicals can cause burns on the skin, damage the eyes and release harmful fumes if used carelessly.
They can also react dangerously with metals or other substances.
Therefore, they should be handled with care, in small quantities, with proper safety equipment and under the guidance of a teacher or trained person.
Q50.Summarise why the study of chemical effects of electric current is important for us.
The study of chemical effects of electric current helps us understand how electricity can bring about chemical changes in solutions.
It explains useful processes like electroplating and metal purification, teaches us about safe use of electricity in liquids,
and shows how science is applied in industries, daily-life products and environmental protection.
This knowledge is essential for both exams and real-life applications.
These 50 topic-wise Short Answer Type Questions with solutions cover all major concepts, activities and applications from
Chapter 14: Chemical Effects of Electric Current of the NCERT Class 8 Science textbook,
making them highly useful for CBSE Class 8 board exams standard preparation.