Summary and Question Answer of NCERT Class 8 Science Chapter 14, Titled “Chemical Effects of Electric Current"

Summary and Question Answer of NCERT Class 8 Science Chapter 14, Titled “Chemical Effects of Electric Current"


Summary/Question and Answer (Very Short Answer Question, Short Answer Question, Long Answer Question) / Assertion and Reasoning / Fill In the Blanks / Case Study Question and Answer


Chapter 14 - "Chemical Effects of Electric Current" in Class 8 Science NCERT.

Summary/Question and Answer (Very Short Answer Question, Short Answer Question, Long Answer Question) / Assertion and Reasoning / Fill In the Blanks / Case Study Question and Answer

1. Introduction to Chemical Effects of Electric Current:

Electricity is not just about lighting bulbs or running appliances; it can also cause chemical changes in certain materials. When electricity passes through substances, it can lead to chemical reactions. This phenomenon is called the chemical effect of electric current.

2. Conductors and Non-Conductors:

  • Conductors: These are materials that allow electric current to pass through them. Metals like copper, aluminum, and iron are good conductors of electricity.
  • Non-Conductors (Insulators): These materials do not allow electricity to pass through them. Rubber, plastic, and wood are examples of insulators.

3. Electrolytes and Non-Electrolytes:

  • Electrolytes: These are substances that conduct electricity when dissolved in water because they form ions. Common electrolytes include acids, bases, and salts.
  • Non-Electrolytes: Substances that do not dissociate into ions in solution and do not conduct electricity. Examples include sugar and alcohol.

4. Electroplating:

Electroplating is a process of depositing a layer of any desired metal on another material by means of electricity. It is used for various purposes such as preventing corrosion, making objects more attractive, and providing a durable coating on objects.

How Electroplating Works:

  1. Setup: The object to be electroplated is made the cathode (negative electrode) in an electrolytic cell. The metal to be plated is made the anode (positive electrode).
  2. Electrolyte: The electrolyte is a solution containing ions of the metal to be plated.
  3. Process: When electric current is passed through the electrolyte, metal ions from the anode are deposited on the cathode, forming a layer of the metal on the object.

5. Chemical Effects of Electric Current in Daily Life:

  • Electroplating: Used in making jewelry, silverware, and chrome-plating on automobiles.
  • Electrolysis: Used for electroplating, electro-refining of metals, and in the extraction of some metals from their ores.

6. Safety Measures in Electroplating:

Since electroplating involves the use of chemicals and electricity, it is crucial to follow safety precautions. Proper ventilation, safety goggles, and gloves are essential. Direct skin contact with chemicals should be avoided.

7. Electroplating and Its Uses:

Various industries utilize electroplating for making decorative items, preventing corrosion, and enhancing the quality of objects. For example, copper is electroplated on electrical wires to prevent them from rusting.

8. Applications of Electroplating in Industries:

  • Decorative Purposes: Electroplating is used for making decorative items such as jewelry and utensils.
  • Corrosion Prevention: Objects like car parts and pipes are electroplated to prevent them from corroding.
  • Enhancing Durability: Objects like coins and medals are electroplated to enhance their durability.

9. Summary and Revision:

The chapter concludes with a summary of the key points learned, encouraging students to revise the concepts of chemical effects of electric current.

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Question and Answer

Fill in the blanks.

(a) Most liquids that conduct electricity are solutions of acids, bases, and salts.

(b) The passage of an electric current through a solution causes chemical effects.

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

(d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

 

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


Answer: When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection because the solution allows the flow of electric current, which creates a magnetic field around the conductor.

Question 3.
Name three liquids, which when tested in the manner shown in Fig. 14.5. may cause the magnetic needle to deflect.

Answer: Three liquids that may cause the magnetic needle to deflect in the manner shown in Fig. 14.5 are acidic solutions, basic solutions, and salt solutions.

Question 4.
The bulb does not glow in the setup shown in Fig. 14.6. List the possible reasons. Explain your answer.

Answer: The bulb does not glow in the setup shown in Fig. 14.6 due to possible reasons like an open circuit, a faulty bulb, or improper connections. The exact reason should be investigated.

Question 5.
A tester is used to check the conduction of electricity through two liquids, labelled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that
(i) liquid A is a better conductor than liquid B.
(ii) liquid B is a better conductor than liquid A.
(iii) both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this manner.

Answer: (i) liquid A is a better conductor than liquid B. The brightness of the bulb indicates the conductivity, and a brighter glow means better conductivity.

Question 6.
Does pure water conduct electricity? If not, what can we do to make it conducting?

Answer: Pure water does not conduct electricity. To make it conducting, we can add impurities or electrolytes like salt or acids.

Question 7.
In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Answer: Shutting off the main electrical supply before using water hoses during a fire is essential to prevent electrical accidents due to water acting as a conductor and causing electric shocks.

Question 8.
A child staying in a coastal region test the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you ex¬plain the reason?

Answer: The compass needle deflects more in seawater because it contains more dissolved salts and ions, making it a better conductor of electricity than drinking water.

Question 9.
Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Answer: It is not safe for an electrician to carry out electrical repairs outdoors during heavy downpour due to the risk of electric shock. Water can conduct electricity, increasing the danger.

Question 10.
Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle showed deflection. What could be the reasons?

Answer: The deflection of the compass needle in rainwater could be due to dissolved impurities or ions, making it a conductor, unlike distilled water.

Question 11.
Prepare a list of objects around you that are electroplated.

Answer: Objects around us that are electroplated include jewelry, coins, cutlery, car parts, and decorative items.

Question 12.
The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

Answer: The thin copper plate should be attached to the positive terminal of the battery. This is because during electrolysis, the metal to be plated (copper in this case) should be connected to the positive terminal to attract the negatively charged ions and deposit pure copper on the thin plate.

 

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20 one-mark very short answer questions related to the chapter "Chemical Effects of Electric Current" along with their concise answers:

Question 1: What is the process of depositing a layer of metal on an object using electricity called?

Answer: Electroplating.

Question 2: Which type of solutions can conduct electricity?

Answer: Acidic, basic, and salt solutions.

Question 3: Name the device used to check the flow of electric current through a circuit.

Answer: Tester.

Question 4: What happens to the magnetic needle of a compass when an electric current flows through it?

Answer: It deflects.

Question 5: Why do we shut off the main electrical supply during a fire?

Answer: To prevent electric shocks due to water conducting electricity.

Question 6: What happens when electricity is passed through copper sulphate solution?

Answer: Copper gets deposited on the electrode connected to the negative terminal of the battery.

Question 7: Which metal is commonly used for electroplating iron objects to prevent rusting?

Answer: Zinc.

Question 8: Why do ionic compounds have high melting points?

Answer: Due to strong electrostatic forces between ions.

Question 9: Which gas is evolved at the anode during the electrolysis of water?

Answer: Oxygen.

Question 10: Why is the process of electroplating useful?

Answer: It enhances the appearance and prevents corrosion of objects.

Question 11: Can pure water conduct electricity?

Answer: No, it is a poor conductor.

Question 12: What is the purpose of adding impurities to water to make it conducting?

Answer: To create ions for conduction of electricity.

Question 13: What is the function of electrolytes in an electrolytic cell?

Answer: They provide ions for the conduction of electricity.

Question 14: Which electrode is connected to the positive terminal of the battery during electroplating?

Answer: Object to be plated.

Question 15: What is the product of the electrolysis of water?

Answer: Hydrogen gas and oxygen gas.

Question 16: Name the process used for obtaining a metal from its oxide.

Answer: Reduction.

Question 17: What is the unit of electric current?

Answer: Ampere (A).

Question 18: Name a liquid that does not conduct electricity.

Answer: Cooking oil.

Question 19: Why do we need to clean the object before electroplating it?

Answer: To remove dirt and ensure proper adhesion of the plated layer.

Question 20: Which metal is often used as the electrode in electrorefining of metals like copper?

Answer: Copper.

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10 two-marks short answer questions related to the chapter "Chemical Effects of Electric Current" along with their brief answers:

Question 1: Explain why metals are good conductors of electricity.

Answer: Metals are good conductors because they have free electrons in their outermost shells that can move easily, allowing the flow of electric current.

Question 2: How does the chemical effect of electric current help in electroplating?

Answer: In electroplating, the metal to be plated acts as the cathode, and metal ions from the solution are reduced and deposited on the cathode, forming a layer and enhancing the object's properties.

Question 3: Why is copper usually used for making electrical wires?

Answer: Copper is used for wires because it is an excellent conductor of electricity, has low resistance, and does not corrode easily, ensuring efficient and durable electrical connections.

Question 4: What happens when electricity is passed through water? Write the chemical equation for the reaction that takes place.

Answer: Water undergoes electrolysis, forming hydrogen gas at the cathode and oxygen gas at the anode. The chemical equation is: 2�2�(�)→2�2(�)+�2(�)2H2​O(l)→2H2​(g)+O2​(g).

Question 5: Why is electroplating done on objects made of iron?

Answer: Electroplating is done on iron objects to prevent them from rusting. A layer of a more reactive metal like zinc is plated on the iron, acting as a protective barrier against corrosion.

Question 6: Explain why pure water does not conduct electricity, but a solution of salt in water does.

Answer: Pure water does not conduct electricity because it lacks ions. Saltwater, on the other hand, contains dissolved ions, allowing the flow of electric current.

Question 7: How does the process of electrorefining purify impure metals?

Answer: Electrorefining involves the electrolysis of impure metal to dissolve it at the anode and deposit pure metal at the cathode, purifying it by removing impurities.

Question 8: What safety precautions should be taken while working with electricity in a laboratory?

Answer: Safety precautions include wearing rubber gloves, using insulated tools, ensuring dry conditions, and avoiding contact with water to prevent electric shocks.

Question 9: Why do metal objects plated with gold retain their shine and do not corrode easily?

Answer: Gold-plated objects do not corrode easily because gold is highly unreactive, and the thin layer of gold acts as a protective barrier, preventing oxidation and corrosion of the underlying metal.

Question 10: Explain the role of electrolytes in the conduction of electricity in liquids.

Answer: Electrolytes dissociate into ions in solution, allowing the flow of electric current. The movement of these ions facilitates the conduction of electricity in liquids.

 

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10 three-marks long answer questions related to the chapter "Chemical Effects of Electric Current" along with their detailed answers:

Question 1: Describe the process of electroplating. Explain its applications and importance in daily life.

Answer: Electroplating is the process of depositing a thin layer of metal on an object using electricity. It finds applications in enhancing the appearance of objects, preventing corrosion, and creating conductive surfaces in electronics. For instance, it's used in making decorative items, jewelry, and coating car parts, making objects more durable and aesthetically pleasing.

Question 2: Explain why water from rivers and lakes conducts electricity while pure water does not.

Answer: Water from rivers and lakes contains dissolved salts and minerals, forming ions that allow the conduction of electricity. Pure water lacks these ions, making it a poor conductor. The presence of impurities in natural water sources enables the flow of electric current.

Question 3: Describe an experiment to show that electricity can pass through a solution and decompose it into its constituents.

Answer: One can set up a simple electrolysis experiment using a solution (e.g., water) and two electrodes (usually copper or carbon rods). Passing electric current through the solution results in the decomposition of water into hydrogen and oxygen gases, collected at the cathode and anode respectively.

Question 4: Explain why the process of electroplating is essential in the preservation of certain metal objects.

Answer: Electroplating provides a protective layer on metal objects, preventing them from rusting or corroding. For example, iron objects are often electroplated with zinc to form a zinc coating, which acts as a barrier against moisture and corrosion, extending the lifespan of the object.

Question 5: Discuss the safety precautions that need to be taken while working with electricity in laboratories and homes.

Answer: Safety precautions include wearing rubber gloves, using insulated tools, ensuring dry conditions, turning off the power supply before working, and avoiding contact with water. These measures prevent electric shocks and accidents, ensuring safe working conditions.

Question 6: Explain why gold and silver are not used for making electrical wires, while copper and aluminum are preferred.

Answer: Gold and silver are excellent conductors, but they are expensive. Copper and aluminum are also good conductors and cost-effective. Hence, they are preferred for making electrical wires, balancing conductivity and cost efficiency.

Question 7: Describe the process of electrorefining with the help of an example. Explain its significance in obtaining pure metals.

Answer: Electrorefining involves dissolving an impure metal (e.g., copper) at the anode and depositing pure metal at the cathode. During electrolysis, impurities settle down, and pure metal is collected, ensuring high purity. Electrorefining is vital in obtaining pure metals for various industrial applications.

Question 8: Explain why metals like sodium and potassium are stored in kerosene oil.

Answer: Sodium and potassium are highly reactive with moisture and air. Storing them in kerosene oil prevents their exposure to these elements, ensuring they remain chemically unreactive and do not react with oxygen or water vapor in the air.

Question 9: Discuss the impact of electroplating on the environment. Mention any measures that can be taken to minimize the environmental impact.

Answer: Electroplating can lead to environmental pollution due to the disposal of chemicals. Proper waste management, recycling of plating solutions, and implementing wastewater treatment methods are crucial. Additionally, using eco-friendly plating processes and materials can minimize environmental harm.

Question 10: Explain the role of electrolysis in the process of electroplating. How does the choice of electrolyte affect the quality of electroplated objects?

Answer: Electrolysis in electroplating involves the reduction of metal ions at the cathode, forming a plated layer. The choice of electrolyte affects the plating process and the quality of the plated object. An appropriate electrolyte provides the desired metal ions for deposition, ensuring a smooth, uniform, and adherent coating, enhancing the quality of electroplated objects.

 

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10 Five-marks long answer questions related to the chapter "Chemical Effects of Electric Current" along with their detailed answers:

Question 1: Explain the process of electrolysis. Provide an example of an electrolytic cell and discuss the reactions occurring at the anode and cathode.

Answer: Electrolysis is the process of using electric current to drive a non-spontaneous chemical reaction. For example, in the electrolysis of water, when a direct current is passed through water, it decomposes into hydrogen gas at the cathode and oxygen gas at the anode. At the cathode, 2�2�(�)+2�−→�2(�)+2��−(��)2H2​O(l)+2e−→H2​(g)+2OH−(aq), and at the anode, 2�2�(�)→�2(�)+4�+(��)+4�−2H2​O(l)→O2​(g)+4H+(aq)+4e−.

Question 2: Discuss the concept of conductivity. Explain why some substances conduct electricity while others do not.

Answer: Conductivity is the ability of a substance to allow electric current to pass through it. Substances conduct electricity when they have free-moving ions or electrons. For example, acids, bases, and salts in their aqueous forms are conductive due to the presence of ions. In contrast, pure water, oils, and non-metallic solids do not conduct electricity because they lack free ions or electrons.

Question 3: Describe an experiment to demonstrate the chemical effect of electric current. Include the materials required and the observations made during the experiment.

Answer: One experiment involves the electrolysis of copper sulfate solution using copper electrodes. When a direct current is passed, copper gets deposited at the cathode (positive electrode) and copper ions dissolve at the anode (negative electrode). The cathode gains mass, while the anode loses mass due to the dissolution of copper ions.

Question 4: Explain the process of electrorefining with the help of an example. How does it help in obtaining pure metals?

Answer: Electrorefining involves the electrolysis of impure metal to dissolve it at the anode and deposit pure metal at the cathode. For instance, in the electrorefining of copper, impure copper acts as the anode, dissolving to form copper ions, which then plate onto a pure copper cathode. This process removes impurities, resulting in high-purity copper for industrial use.

Question 5: Discuss the applications of electroplating in different industries. How does electroplating benefit these industries?

Answer: Electroplating is widely used in industries such as jewelry, automobile, and electronics. In jewelry, it enhances aesthetics; in the automobile industry, it prevents corrosion, and in electronics, it creates conductive layers. Electroplating provides a protective coating, enhancing durability and appearance in various products.

Question 6: Explain the factors affecting the quality of electroplated objects. What measures can be taken to improve the quality of electroplated products?

Answer: Factors affecting electroplated objects include temperature, current density, cleanliness, and composition of plating solution. Quality can be improved by ensuring proper cleaning of objects, maintaining appropriate current density, regulating bath temperature, and using high-quality plating solutions, resulting in uniform and smooth coatings.

Question 7: Discuss the importance of electrolysis in various industrial processes. Provide examples of industrial applications where electrolysis is essential.

Answer: Electrolysis is vital in industries for various applications. In the production of aluminum, electrolysis is used to extract pure aluminum from aluminum oxide. Similarly, electrolysis is crucial in the chlor-alkali industry for producing chlorine gas, hydrogen gas, and sodium hydroxide, essential chemicals for numerous industrial processes.

Question 8: Explain why copper wires are preferred over iron wires in electrical connections. How does the chemical property of copper contribute to its suitability for this purpose?

Answer: Copper wires are preferred over iron wires due to copper's excellent conductivity, low resistance, and resistance to corrosion. Copper does not corrode easily, ensuring stable and efficient electrical connections. Its high conductivity allows the smooth flow of electric current, making it ideal for various electrical applications.

Question 9: Discuss the environmental impact of electroplating. What measures can industries adopt to minimize the environmental consequences of electroplating processes?

Answer: Electroplating can lead to environmental pollution due to chemical discharge. Industries can adopt closed-loop systems, proper waste disposal, and use eco-friendly plating solutions. Effluent treatment plants can help in treating wastewater, ensuring that harmful chemicals do not contaminate natural water bodies.

Question 10: Explain the safety precautions that should be followed while working with electrolytes and electrical equipment. Why is it essential to follow these precautions?

Answer: Safety precautions include wearing protective gear, working in dry conditions, and using insulated tools. It's crucial to prevent accidents, including electric shocks and chemical exposure. Following these precautions ensures the well-being of workers, minimizing the risks associated with working with electrolytes and electrical equipment.

 

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Multiple-Choice Questions (MCQs): Set 1

1. What is the purpose of electroplating? A) To produce electricity
B) To prevent corrosion and for decorative purposes
C) To generate heat
D) To produce sound

Answer: B) To prevent corrosion and for decorative purposes
Explanation: Electroplating is used to prevent corrosion, enhance the appearance of objects, and for decorative purposes.

2. Which of the following is a good conductor of electricity? A) Wood
B) Plastic
C) Copper
D) Rubber

Answer: C) Copper
Explanation: Copper is a metal and is an excellent conductor of electricity.

3. Which of the following is a non-electrolyte? A) Salt solution
B) Sugar solution
C) Vinegar solution
D) Hydrochloric acid solution

Answer: B) Sugar solution
Explanation: Sugar solution does not dissociate into ions in water and therefore does not conduct electricity.

4. What is the process of depositing a layer of metal on another material using electricity called? A) Electrolysis
B) Electroplating
C) Electromagnetism
D) Electrolytic cell

Answer: B) Electroplating
Explanation: Electroplating is the process of depositing a layer of metal on another material using electricity.

5. Which metal is commonly used for electroplating iron objects to prevent rusting? A) Gold
B) Copper
C) Silver
D) Zinc

Answer: D) Zinc
Explanation: Zinc is commonly used to electroplate iron objects to prevent rusting; this process is known as galvanization.

6. Which of the following is an example of an electrolyte? A) Sugar solution
B) Distilled water
C) Salt solution
D) Oil

Answer: C) Salt solution
Explanation: Salt solution dissociates into ions in water, making it an electrolyte.

7. What is the purpose of safety measures in electroplating? A) To make the process faster
B) To avoid accidents and protect workers
C) To increase the cost of electroplating
D) To improve the quality of the plating

Answer: B) To avoid accidents and protect workers
Explanation: Safety measures are essential to prevent accidents and protect the workers involved in electroplating.

8. What happens when electricity is passed through water containing electrolytes? A) Water freezes
B) Water evaporates
C) Electrolysis occurs
D) Water turns into a gas

Answer: C) Electrolysis occurs
Explanation: Electrolysis occurs when electricity is passed through water containing electrolytes, leading to the decomposition of water into hydrogen and oxygen gases.

9. Which of the following is an example of a non-conductor (insulator)? A) Copper
B) Rubber
C) Silver
D) Aluminum

Answer: B) Rubber
Explanation: Rubber is an insulator; it does not allow electric current to pass through.

10. What is the chemical formula for table salt? A) NaOH
B) HCl
C) NaCl
D) H2SO4

Answer: C) NaCl
Explanation: The chemical formula for table salt (sodium chloride) is NaCl.

11. Which metal is commonly used for electroplating car parts and bathroom fittings? A) Copper
B) Gold
C) Chromium
D) Iron

Answer: C) Chromium
Explanation: Chromium is commonly used for electroplating car parts and bathroom fittings to prevent corrosion.

12. Why is it important to wear safety goggles and gloves during electroplating? A) To look professional
B) To avoid accidents and protect eyes and hands from chemicals
C) To improve the quality of plating
D) To increase the speed of electroplating

Answer: B) To avoid accidents and protect eyes and hands from chemicals
Explanation: Wearing safety goggles and gloves protects the eyes and hands of workers from coming into direct contact with chemicals used in electroplating, preventing accidents.

13. Which of the following substances is a non-electrolyte? A) Hydrochloric acid
B) Vinegar (acetic acid)
C) Sodium chloride
D) Sulfuric acid

Answer: B) Vinegar (acetic acid)
Explanation: Vinegar (acetic acid) is a non-electrolyte; it does not dissociate into ions in solution.

14. What is the purpose of electro-refining in the extraction of metals? A) To produce electricity
B) To obtain pure metal from impure metal
C) To generate heat
D) To increase the conductivity of metals

Answer: B) To obtain pure metal from impure metal
Explanation: Electro-refining is used to obtain pure metal from impure metal by passing electric current through a solution containing the metal ions.

15. Why is copper electroplated on electrical wires? A) To make them heavy
B) To make them soft
C) To prevent them from rusting
D) To make them colorful

Answer: C) To prevent them from rusting
Explanation: Copper is electroplated on electrical wires to prevent them from rusting and to enhance their conductivity.

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Multiple-Choice Questions (MCQs): Set 2

1. What is the chemical formula for hydrochloric acid? A) HCl
B) NaCl
C) H2SO4
D) CH3COOH

Answer: A) HCl
Explanation: The chemical formula for hydrochloric acid is HCl.

2. Which metal is commonly used for electroplating silverware? A) Gold
B) Silver
C) Platinum
D) Nickel

Answer: B) Silver
Explanation: Silver is commonly used for electroplating silverware to enhance its appearance.

3. What happens when electricity is passed through copper sulfate solution using copper electrodes? A) Copper ions from the solution are deposited on the cathode
B) Copper ions from the anode enter the solution
C) Copper ions from the cathode enter the solution
D) Copper ions from the anode are deposited on the cathode

Answer: A) Copper ions from the solution are deposited on the cathode
Explanation: Copper ions from the solution are reduced and deposited on the cathode during electrolysis.

4. What is the purpose of adding a small amount of sulfuric acid to the electrolyte in a lead-acid battery? A) To make the battery heavy
B) To improve the conductivity of the battery
C) To increase the voltage of the battery
D) To activate the electrolyte

Answer: D) To activate the electrolyte
Explanation: Sulfuric acid activates the electrolyte in a lead-acid battery, allowing it to conduct electricity.

5. Which of the following metals is commonly used for electroplating iron objects to prevent rusting? A) Silver
B) Copper
C) Zinc
D) Gold

Answer: C) Zinc
Explanation: Zinc is commonly used for electroplating iron objects to prevent rusting; this process is known as galvanization.

6. Which of the following is a non-metal that conducts electricity? A) Copper
B) Aluminum
C) Graphite
D) Silver

Answer: C) Graphite
Explanation: Graphite is a non-metal that conducts electricity due to the presence of free electrons.

7. What is the chemical formula for table sugar (sucrose)? A) C6H12O6
B) NaCl
C) C12H22O11
D) H2SO4

Answer: C) C12H22O11
Explanation: The chemical formula for table sugar (sucrose) is C12H22O11.

8. Which of the following is a poor conductor of electricity? A) Copper
B) Silver
C) Wood
D) Aluminum

Answer: C) Wood
Explanation: Wood is a poor conductor of electricity.

9. Which gas is evolved at the cathode during the electrolysis of water? A) Oxygen
B) Hydrogen
C) Nitrogen
D) Carbon dioxide

Answer: B) Hydrogen
Explanation: Hydrogen gas is evolved at the cathode during the electrolysis of water.

10. What is the purpose of using an electrolyte in an electrolytic cell? A) To increase the temperature
B) To prevent chemical reactions
C) To facilitate the flow of electric current
D) To decrease the conductivity

Answer: C) To facilitate the flow of electric current
Explanation: Electrolytes facilitate the flow of electric current in an electrolytic cell by providing ions for the conduction of electricity.

11. Which of the following is an example of an electroplated object? A) Aluminum foil
B) Iron nail with a zinc coating
C) Wooden table
D) Plastic ruler

Answer: B) Iron nail with a zinc coating
Explanation: An iron nail with a zinc coating is an example of an electroplated object.

12. What is the chemical symbol for silver? A) Si
B) Ag
C) Au
D) Al

Answer: B) Ag
Explanation: The chemical symbol for silver is Ag (from the Latin word "argentum").

13. Which of the following substances does not conduct electricity in the solid state? A) Copper
B) Iron
C) Wood
D) Graphite

Answer: C) Wood
Explanation: Wood is a poor conductor of electricity, even in the solid state.

14. Which of the following is used as a negative electrode in electroplating? A) Anode
B) Cathode
C) Both A and B
D) Neither A nor B

Answer: B) Cathode
Explanation: The cathode is the negative electrode in electroplating where metal ions from the solution are deposited.

15. What is the chemical symbol for gold? A) G
B) Ag
C) Au
D) Pt

Answer: C) Au
Explanation: The chemical symbol for gold is Au (from the Latin word "aurum").

1. What is the chemical formula for hydrochloric acid? A) HCl
B) NaCl
C) H2SO4
D) CH3COOH

Answer: A) HCl
Explanation: The chemical formula for hydrochloric acid is HCl.

2. Which metal is commonly used for electroplating silverware? A) Gold
B) Silver
C) Platinum
D) Nickel

Answer: B) Silver
Explanation: Silver is commonly used for electroplating silverware to enhance its appearance.

3. What happens when electricity is passed through copper sulfate solution using copper electrodes? A) Copper ions from the solution are deposited on the cathode
B) Copper ions from the anode enter the solution
C) Copper ions from the cathode enter the solution
D) Copper ions from the anode are deposited on the cathode

Answer: A) Copper ions from the solution are deposited on the cathode
Explanation: Copper ions from the solution are reduced and deposited on the cathode during electrolysis.

4. What is the purpose of adding a small amount of sulfuric acid to the electrolyte in a lead-acid battery? A) To make the battery heavy
B) To improve the conductivity of the battery
C) To increase the voltage of the battery
D) To activate the electrolyte

Answer: D) To activate the electrolyte
Explanation: Sulfuric acid activates the electrolyte in a lead-acid battery, allowing it to conduct electricity.

5. Which of the following metals is commonly used for electroplating iron objects to prevent rusting? A) Silver
B) Copper
C) Zinc
D) Gold

Answer: C) Zinc
Explanation: Zinc is commonly used for electroplating iron objects to prevent rusting; this process is known as galvanization.

6. Which of the following is a non-metal that conducts electricity? A) Copper
B) Aluminum
C) Graphite
D) Silver

Answer: C) Graphite
Explanation: Graphite is a non-metal that conducts electricity due to the presence of free electrons.

7. What is the chemical formula for table sugar (sucrose)? A) C6H12O6
B) NaCl
C) C12H22O11
D) H2SO4

Answer: C) C12H22O11
Explanation: The chemical formula for table sugar (sucrose) is C12H22O11.

8. Which of the following is a poor conductor of electricity? A) Copper
B) Silver
C) Wood
D) Aluminum

Answer: C) Wood
Explanation: Wood is a poor conductor of electricity.

9. Which gas is evolved at the cathode during the electrolysis of water? A) Oxygen
B) Hydrogen
C) Nitrogen
D) Carbon dioxide

Answer: B) Hydrogen
Explanation: Hydrogen gas is evolved at the cathode during the electrolysis of water.

10. What is the purpose of using an electrolyte in an electrolytic cell? A) To increase the temperature
B) To prevent chemical reactions
C) To facilitate the flow of electric current
D) To decrease the conductivity

Answer: C) To facilitate the flow of electric current
Explanation: Electrolytes facilitate the flow of electric current in an electrolytic cell by providing ions for the conduction of electricity.

11. Which of the following is an example of an electroplated object? A) Aluminum foil
B) Iron nail with a zinc coating
C) Wooden table
D) Plastic ruler

Answer: B) Iron nail with a zinc coating
Explanation: An iron nail with a zinc coating is an example of an electroplated object.

12. What is the chemical symbol for silver? A) Si
B) Ag
C) Au
D) Al

Answer: B) Ag
Explanation: The chemical symbol for silver is Ag (from the Latin word "argentum").

13. Which of the following substances does not conduct electricity in the solid state? A) Copper
B) Iron
C) Wood
D) Graphite

Answer: C) Wood
Explanation: Wood is a poor conductor of electricity, even in the solid state.

14. Which of the following is used as a negative electrode in electroplating? A) Anode
B) Cathode
C) Both A and B
D) Neither A nor B

Answer: B) Cathode
Explanation: The cathode is the negative electrode in electroplating where metal ions from the solution are deposited.

15. What is the chemical symbol for gold? A) G
B) Ag
C) Au
D) Pt

Answer: C) Au
Explanation: The chemical symbol for gold is Au (from the Latin word "aurum").

 

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Assertion and Reasoning Question

1. Assertion: Electroplating is a method used to prevent corrosion and enhance the appearance of metal objects.
Reasoning: During electroplating, a metal coating is deposited on the object, protecting it from corrosion and improving its visual appeal.

Explanation:
Assertion and Reasoning are both correct. Electroplating involves the deposition of a thin layer of metal on objects, preventing them from corroding and enhancing their appearance.

2. Assertion: Electrolytes are substances that conduct electricity in their molten state but not in their aqueous solution.
Reasoning: Electrolytes in molten state have free ions that facilitate the flow of electricity, but when dissolved in water, they do not conduct electricity.

Explanation:
Assertion is incorrect. Electrolytes conduct electricity both in their molten state and in their aqueous solution, where they dissociate into ions.

3. Assertion: During electrolysis of water, oxygen is evolved at the cathode.
Reasoning: Water molecules dissociate into hydrogen ions and oxygen ions during electrolysis.

Explanation:
Assertion is incorrect. During electrolysis of water, hydrogen gas is evolved at the cathode, not oxygen. Water dissociates into hydrogen ions and hydroxide ions.

4. Assertion: Electroplating with silver is commonly used in the production of coins.
Reasoning: Silver-plated coins are more valuable than regular coins.

Explanation:
Assertion and Reasoning are both incorrect. Electroplating with copper, not silver, is commonly used in the production of coins to prevent corrosion and enhance durability.

5. Assertion: Electrolysis is the process of breaking down a substance into its constituent elements using electricity.
Reasoning: Electrolysis occurs only in liquids.

Explanation:
Assertion is correct, but Reasoning is incorrect. Electrolysis is the process of breaking down a substance into its constituent elements or ions using electricity. It can occur in both liquids and molten state.

6. Assertion: Electroplating is a reversible process.
Reasoning: The metal layer deposited during electroplating can be removed easily.

Explanation:
Assertion is incorrect. Electroplating is not a reversible process; the metal layer cannot be easily removed without damaging the object.

7. Assertion: Electrolysis of water results in the formation of hydrogen ions and oxygen ions.
Reasoning: Hydrogen ions are positively charged, and oxygen ions are negatively charged.

Explanation:
Assertion is incorrect. During electrolysis of water, hydrogen ions and hydroxide ions are formed. Hydrogen ions are positively charged, and hydroxide ions are negatively charged.

8. Assertion: Electroplating is used to coat iron objects with a layer of zinc to prevent rusting.
Reasoning: Zinc-plated iron objects do not corrode easily.

Explanation:
Assertion and Reasoning are both correct. Electroplating iron objects with a layer of zinc (galvanization) prevents rusting and corrosion.

9. Assertion: Electroplating is used for decorative purposes, but it does not improve the durability of objects.
Reasoning: Electroplated objects are prone to chipping and wear.

Explanation:
Assertion is incorrect. Electroplating is used for both decorative purposes and to enhance the durability of objects, making them more resistant to corrosion and wear.

10. Assertion: Electrolysis can occur in both molten and aqueous solutions.
Reasoning: In molten solutions, ions are fixed and do not move.

Explanation:
Assertion is correct, but Reasoning is incorrect. Electrolysis can indeed occur in both molten and aqueous solutions. In molten solutions, ions are mobile and can conduct electricity.

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Assertion and Reasoning Question

1. Assertion: Electroplating is a useful process for protecting iron objects from rusting.
Reasoning: A layer of metal is coated over iron objects during electroplating, preventing direct exposure to air and moisture.

Explanation:
Assertion and Reasoning are both correct. Electroplating creates a protective layer on iron objects, preventing them from direct contact with corrosive elements.

2. Assertion: Electrolysis is the process of breaking down a substance using electricity.
Reasoning: Electrolysis involves the formation of chemical bonds between atoms.

Explanation:
Assertion is correct, but Reasoning is incorrect. Electrolysis is indeed the process of breaking down substances into their constituent elements or ions using electricity.

3. Assertion: Electroplating is commonly used in the automotive industry to enhance the appearance of vehicles.
Reasoning: Electroplating allows for the application of a thin layer of metal on various parts of vehicles.

Explanation:
Assertion and Reasoning are both correct. Electroplating is widely used in the automotive industry to add decorative and protective layers to vehicle parts.

4. Assertion: Electrolysis can be used to extract certain metals from their ores.
Reasoning: Electrolysis allows for the separation of metals from their compounds by passing an electric current through the compound.

Explanation:
Assertion and Reasoning are both correct. Electrolysis is used in the extraction of certain metals from their ores by breaking the metal compounds using electricity.

5. Assertion: Electroplating is a permanent process, and the plated layer cannot be removed easily.
Reasoning: The plated layer is firmly bonded with the object during electroplating.

Explanation:
Assertion and Reasoning are both correct. Electroplating creates a strong bond between the plated layer and the object, making it a permanent process.

6. Assertion: Electrolytes are necessary for the conduction of electricity in an electrolytic cell.
Reasoning: Electrolytes provide a medium for the movement of ions, allowing electric current to pass through the cell.

Explanation:
Assertion and Reasoning are both correct. Electrolytes provide ions for the conduction of electricity in an electrolytic cell.

7. Assertion: Electroplating with gold is commonly used in the production of jewelry.
Reasoning: Gold-plated jewelry is more affordable than solid gold jewelry.

Explanation:
Assertion and Reasoning are both correct. Electroplating with gold is used to make jewelry more affordable, as the plated layer reduces the amount of gold used.

8. Assertion: Electrolysis of water results in the formation of hydrogen gas at the anode.
Reasoning: Hydrogen ions are positively charged and migrate to the anode during electrolysis.

Explanation:
Assertion is incorrect. During electrolysis of water, hydrogen gas is formed at the cathode, not the anode. Hydroxide ions migrate to the anode.

9. Assertion: Electroplating is an irreversible process.
Reasoning: The metal coating applied during electroplating cannot be removed without damaging the object.

Explanation:
Assertion is correct, but Reasoning is incorrect. Electroplating is indeed an irreversible process; the metal coating cannot be easily removed without damaging the object.

10. Assertion: Electrolysis is used in electrorefining to purify metals.
Reasoning: Electrolysis allows impurities to dissolve into the electrolyte, leaving behind pure metal.

Explanation:
Assertion and Reasoning are both correct. Electrolysis in electrorefining dissolves impurities, purifying the metal and leaving behind a pure substance.

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Top of Form

 

Case Study 1: Electroplating in Everyday Life

Case Study: A jewelry workshop in your town specializes in electroplating gold and silver jewelry. The owner uses this technique not only for enhancing the aesthetics of the jewelry but also to prevent tarnishing and corrosion. Analyze the process and its applications in different types of jewelry.

Questions:

  1. Question: Why is electroplating commonly used in the jewelry industry?

Answer: Electroplating is used in the jewelry industry to enhance the appearance of jewelry items and prevent tarnishing and corrosion. A thin layer of metal is deposited on the surface of jewelry items using this technique.

  1. Question: How does electroplating prevent jewelry from tarnishing?

Answer: Electroplating creates a protective layer on jewelry, preventing direct contact with air and moisture, which are the causes of tarnishing. The plated layer acts as a barrier, preserving the original shine of the jewelry.

  1. Question: Mention one other industry where electroplating is commonly used and explain its purpose.

Answer: Electroplating is commonly used in the automotive industry. It is applied on car parts to prevent corrosion, improve durability, and enhance the visual appeal of vehicles.

  1. Question: What precautions should be taken while performing electroplating in a workshop?

Answer: Safety measures such as wearing gloves, safety goggles, and proper ventilation are essential during electroplating. Workers should avoid direct contact with chemicals and be trained in handling equipment safely.

  1. Question: Can you think of an environmental concern related to electroplating? Explain.

Answer: Yes, one environmental concern is the disposal of chemicals used in electroplating. Proper disposal methods need to be employed to prevent contamination of soil and water sources.

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Case Study 2: Electrolysis for Metal Extraction

Case Study: A metal extraction plant in your region uses electrolysis to obtain pure metals from their ores. Explore the electrolytic process used in the plant and its significance in the production of various metals.

Questions:

  1. Question: How does electrolysis assist in the extraction of metals from their ores?

Answer: Electrolysis breaks down metal compounds in ores into their constituent elements using electricity. It separates the metal ions from the compound, allowing the extraction of pure metals.

  1. Question: What is the role of electrodes in the process of electrolysis?

Answer: Electrodes conduct electricity into the electrolyte. The positive electrode (anode) attracts negatively charged ions (anions), and the negative electrode (cathode) attracts positively charged ions (cations), allowing the separation of elements.

  1. Question: Explain one application of electrolysis in the production of a specific metal.

Answer: Electrolysis is used in the production of aluminum. Aluminum oxide dissolved in molten cryolite undergoes electrolysis, resulting in the extraction of pure aluminum at the cathode.

  1. Question: Why is it important to obtain metals in their pure form for industrial applications?

Answer: Pure metals have desirable properties such as high conductivity and malleability, making them essential for various industrial applications, including electronics and construction.

  1. Question: Can you name another method used for metal extraction besides electrolysis? Explain briefly.

Answer: Yes, another method is smelting, where metal ores are heated in a furnace with a reducing agent to extract the metal. The metal melts and is collected as it flows out of the furnace.

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Case Study 3: Electrolysis in Water Treatment

Case Study: A water treatment plant in your city uses electrolysis to disinfect water and make it safe for consumption. Investigate the electrolytic process used and its role in providing clean drinking water.

Questions:

  1. Question: How does electrolysis disinfect water, making it safe for consumption?

Answer: Electrolysis produces chlorine gas, which is a strong disinfectant. When dissolved in water, it forms hypochlorous acid, killing bacteria and other harmful microorganisms, making the water safe to drink.

  1. Question: What is the significance of disinfecting water before it reaches households?

Answer: Disinfecting water is essential to prevent waterborne diseases. It ensures that the water supply is free from harmful microorganisms, safeguarding public health.

  1. Question: Are there any by-products of electrolytic water disinfection? Explain.

Answer: Yes, one by-product is hydrogen gas. Hydrogen gas is formed at the cathode during the electrolysis of water. It can be collected and utilized as a source of energy.

  1. Question: What safety measures should be taken when handling chlorine gas during the electrolysis process?

Answer: Workers should wear appropriate protective gear such as masks and gloves when handling chlorine gas. Proper ventilation in the area is crucial to prevent the accumulation of the gas.

  1. Question: Can you suggest an alternative method for water disinfection besides electrolysis? Explain briefly.

Answer: Yes, another method is ultraviolet (UV) disinfection, where water is exposed to UV light, killing or inactivating microorganisms present in the water.

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Case Study 4: Electrolysis in Electroplating Industries

Case Study: An electroplating factory in your town utilizes electrolysis for coating metal products. Explore the various applications of electroplating in different industries and its impact on the quality of products.

Questions:

  1. Question: How does electroplating enhance the quality and durability of metal products?

Answer: Electroplating forms a protective layer on metal products, preventing corrosion and wear. It enhances the appearance, durability, and longevity of products.

  1. Question: Name two industries other than jewelry where electroplating is widely used. Explain its purpose in each industry.

Answer: Electroplating is used in the automotive industry to prevent corrosion on car parts. It is also used in the electronics industry to create conductive layers on components.

  1. Question: What is the role of electric current in the electroplating process?

Answer: Electric current helps in the deposition of metal ions onto the surface of the object being electroplated. It facilitates the formation of a uniform and adherent metal coating.

  1. Question: Why is it important to clean the object thoroughly before electroplating?

Answer: Thorough cleaning removes dirt, oil, and other impurities from the object's surface. Clean surfaces ensure proper adhesion of the plated layer and prevent defects in the coating.

  1. Question: Can you think of an environmental concern related to electroplating? Explain.

Answer: Yes, one concern is the disposal of electroplating chemicals, which can contaminate soil and water if not managed properly. Effluent treatment methods are essential to mitigate environmental impact.

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Case Study 5: Electrolysis in Electrorefining of Metals

Case Study: A metallurgical plant in your area uses electrolysis for the electrorefining of copper. Explore the electrorefining process and its significance in obtaining high-purity copper for industrial applications.

Questions:

  1. Question: How does electrorefining improve the purity of copper obtained from ores?

Answer: Electrorefining dissolves impure copper from the anode into the electrolyte. Pure copper is deposited at the cathode, resulting in high-purity copper.

  1. Question: Explain why impurities settle at the bottom of the electrolytic cell during electrorefining.

Answer: Impurities in the copper being refined have higher density than copper. Therefore, they settle at the bottom of the cell, separating from the pure copper.

  1. Question: Why is the copper obtained through electrorefining considered high-quality for electrical applications?

Answer: Electrorefined copper is highly pure, with low impurity levels. This purity ensures excellent electrical conductivity, making it ideal for electrical and electronic applications.

  1. Question: What is the role of the electrolyte in the electrorefining process?

Answer: The electrolyte provides copper ions for the conduction of electricity. It enables the movement of copper ions from the anode to the cathode during electrorefining.

  1. Question: Can you name another metal that is refined using the electrorefining process? Explain briefly.

Answer: Yes, another metal refined through electrorefining is silver. It is used to obtain pure silver for various applications, including jewelry and coins.

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These case studies and questions provide students with a comprehensive understanding of the applications and significance of electrolysis and electroplating processes in different industries and contexts.



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