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Chemical Effects of Electric Current (Class VIII)

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Which of the following are strong electrolytes?

a. Acetic acid solution b. Carbonic acid solution c. Nitric acid solution d. Potassium hydroxide solution

  1. Only a and b

  2. Only a and c

  3. Only a and d

  4. Only b and c

  5. Only c and d


Correct Option: E
Explanation:

This is the correct option. Nitric acid solution and potassium hydroxide solution are strong electrolytes. They both contain lots of ions in them.

Which of the following solutions are non-electrolytes?

a. Glucose solution b. Vinegar solution c. Alcohol solution d. Common salt solution

  1. Only a and b

  2. Only a and c

  3. Only a and d

  4. Only b and c

  5. Only b and d


Correct Option: B
Explanation:

This is the correct option. Glucose solution and alcohol solution are non-electrolytes. They are non-conducting liquids.

Which of the following cannot be added to distilled water to make it a good conductor of electricity?

  1. Dilute sulphuric acid

  2. Sodium hydroxide

  3. Lemon juice

  4. Vinegar

  5. Vegetable oil


Correct Option: E
Explanation:

This is the correct option. Vegetable oil cannot be added to distilled water to make it a good conductor of electricity.

In which of the following ways can the weak electric current flowing through liquids, having low conductivity, be detected?

a. By using a torch bulb b. By using an LED c. By using a compass surrounded by turns of circuit wire

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only a and c


Correct Option: D
Explanation:

This is the correct option. The weak electric current flowing through liquids, having low conductivity, can be detected by using an LED and by using a compass surrounded by turns of circuit wire.

When electric current is passed through acidified water by using carbon electrodes, then a chemical reaction takes place to form

  1. hydrogen gas and carbon dioxide gas

  2. hydrogen gas and nitrogen gas

  3. oxygen gas and carbon dioxide gas

  4. hydrogen gas and oxygen gas

  5. carbon dioxide gas and nitrogen gas


Correct Option: D
Explanation:

This is the correct option. When electric current is passed through acidified water by using carbon electrodes, then a chemical reaction takes place to form hydrogen gas and oxygen gas.

Which of the following statements is/are false?

a. Caustic soda is produced by the electrolysis of an aqueous solution of potassium chloride. b. If we take ordinary water in a beaker and pass electricity through it, then the torch bulb will not glow at all even if a large battery is applied. c. A solution of sodium hydroxide or potassium hydroxide in water conducts electricity.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c


Correct Option: A
Explanation:

This is the correct option as this statement is false. Caustic soda is produced by the electrolysis of an aqueous solution of sodium chloride.

Which of the following gases is formed at the anode, which is connected to the positive terminal of the battery when electric current is passed through acidified water?

  1. Hydrogen

  2. Nitrogen

  3. Oxygen

  4. Argon

  5. Helium


Correct Option: C
Explanation:

This is the correct option. Oxygen is formed at the anode, which is connected to the positive terminal of the battery when electric current is passed through acidified water.

When an electric current flows through a conducting solution, it causes a chemical change. The chemical reactions brought about by an electric current will not produce which of the following effects?

a. Change in colour of solution may occur. b. Deposits of metal will be formed on the sides of the container. c. Bubbles of a gas or gases may be formed on the electrodes.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c


Correct Option: C
Explanation:

This is the correct option as the chemical reactions brought about by an electric current will not deposit metal on the sides of the container. It may deposit metal on electrodes.

Which of the following statements is/are incorrect regarding electroplating of an iron object with copper metal?

a. A copper plate is made the positive electrode. b. The iron object, which is to be electroplated, is made the negative electrode. c. Iron sulphate solution is taken as an electrolyte.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c


Correct Option: E
Explanation:

This is the correct option as this statement is false regarding electroplating an iron object with copper metal. Copper sulphate solution, and not iron sulphate solution, is taken as an electrolyte as it contains copper metal in dissolved form as copper ions.

The chemical effect of electric current is not used in the industry for which of the following purposes?

  1. Decomposing chemical compounds

  2. Production of chemical compounds

  3. Purification of metals

  4. Separation of certain metals from the ores

  5. Electroplating metals


Correct Option: D
Explanation:

This is the correct option as the chemical effect of electric current is not used in the industry for the separation of certain metals from the ores. It is used for the production of certain metals from the ores.

Which of the following statements is/are false?

a. The chemical decomposition produced by passing an electric current through a conducting liquid is called electrolysis. b. Due to the presence of small amounts of carbonic acid and nitric acid in the rainwater, it becomes a conductor of electricity. c. Drinking water is a much better conductor of electricity than sea water.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c


Correct Option: E
Explanation:

This is the correct option as this statement is false. Sea water is a much better conductor of electricity than drinking water.

Electroplating is done to protect something from corrosion and for decorative purposes. Which of the following metals cannot be used for electroplating?

  1. Nickel

  2. Chromium

  3. Iron

  4. Copper

  5. Tin


Correct Option: C
Explanation:

This is the correct option. Iron cannot be used for electroplating because it corrodes and rusts.

Which of the following cannot be produced by passing electric current through its compounds in molten state?

  1. Magnesium

  2. Calcium

  3. Sodium

  4. Aluminium

  5. Platinum


Correct Option: E
Explanation:

This is the correct option. Platinum cannot be produced by passing electric current through its compounds in molten state because it is the least reactive metal.

Match the following:

 
a. Electrolyte 1. It is the negatively charged electrode.
b. Anode 2. It is a liquid that can conduct electricity.
c. Cathode 3. It is the positively charged electrode.
  1. a - 2, b - 3, c - 1

  2. a - 2, b - 1, c - 3

  3. a - 1, b - 2, c - 3

  4. a - 3, b - 2, c - 1

  5. a - 1, b - 3, c - 2


Correct Option: A
Explanation:

This is the correct option. Electrolyte is a liquid that can conduct electricity. Anode is the positively charged electrode. Cathode is the negatively charged electrode.

Which of the following statements is/are false?

a. A solution of hydrochloric acid or sulphuric acid in water conducts electricity. b. Vinegar does not conduct electricity as it is a solution of acid. c. An arrangement having two electrodes kept in a conducting liquid in a vessel is called an electrolytic cell.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c


Correct Option: C
Explanation:

This is the correct option as this statement is false. Vinegar does conduct electricity as it is a solution of acid.

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