Chapter 14: Chemical Effects of Electric Current  

Extra Internal Question and Answer :

Question: : What is an electrode? Name the two types of electrodes used in a circuit.

Answer: An electrode is a conductor through which electric current enters or leaves a liquid in a circuit. The two types of electrodes used are the positive electrode (anode) and the negative electrode (cathode).

Question: What is meant by conduction of electricity in liquids?

Answer: Conduction of electricity in liquids means the flow of electric current through a liquid. This happens due to the movement of charged particles (ions) present in the liquid, which allow electricity to pass through it.
Question: Why are acids, bases and salts good conductors of electricity in aqueous solutions?

Answer: Acids, bases and salts conduct electricity in aqueous solutions because they dissociate into charged particles called ions. These ions are free to move in the solution and carry electric current, making the solution a good conductor of electricity.
Question: What is electroplating ? Give one example.

Answer:The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. It is one of the most common applications of chemical effects of electric current. Example: Chromium plating on iron taps.
Question: What are the main components required for electroplating ?

Answer: The main components required for electroplating are a source of electric current, two electrodes (the metal to be coated and the object to be plated), and an electrolyte which is a solution of a salt of the coating metal.
Question: What are the chemical effects of electric current ? Name any two changes produced by the chemical effect of current.

Answer: The passage of an electric current through a conducting liquid causes chemical reactions.The resulting effects are called chemical effects of currents.

Two changes produced by the chemical effect of electric current are:

(a) Deposition of metal on the electrodes.
(b) Change in colour of the solution.

Question: Why is distilled water a poor conductor of electricity ?

Answer: Distilled water is a poor conductor of electricity because it does not contain dissolved salts or minerals. In the absence of ions, electric current cannot pass through it easily. Hence, distilled water does not conduct electricity.
Question: What is the role of a tester in checking conductivity of liquids?

Answer: A tester is used to check whether a liquid conducts electricity or not. When the tester is placed in the liquid, the flow of current is indicated by the glowing of the bulb or deflection of the compass needle, showing that the liquid is a conductor.
Question: What happens when salt is added to pure water? Explain.

Answer: When salt is added to pure water, it dissolves and forms a solution. The dissolved salt produces ions in the water, which help in the flow of electric current. As a result, the solution becomes a good conductor of electricity.

Exercises

1. Fill in the blanks.
(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.
(b) The passage of an electric current through a solution causes ______________ effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the……………… terminal of the battery.
(d) The process of depositing a layer of any desired metal on another material by means of electricity is called………………. .

Answer:  (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.

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 the tester are dipped into the solution, the solution allows electric current to pass through it. This current flows in the circuit and produces a magnetic effect. Due to this magnetic effect, the magnetic needle gets deflected.
3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

Answer: The three liquids that may cause the magnetic needle to deflect are lemon juice, vinegar, and tap water. These liquids contain dissolved ions that allow electric current to pass through them, making them good conductors of electricity.

4. The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.

Answer:  The list of the possible reasons are :

(i) The liquid may be a poor conductor of electricity; it may not allow enough current to pass for the bulb to glow.

(ii) The connections may be loose; if the wires are not properly connected, the circuit will remain open.

(iii) The bulb may be fused; a broken filament will prevent it from glowing.

(iv) The battery may be weak or exhausted; an insufficient power supply will not make the bulb glow.

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 depends on how much current flows through the liquid. Since the bulb glows brightly for liquid A and dimly for liquid B, it means liquid A allows more current to pass ,so it’s a better conductor of electricity than liquid B.]
6. Does pure water conduct electricity? If not, what can we do to make it conducting?

Answer: Pure water does not conduct electricity because it does not contain enough free ions. To make it conducting, we can add a small amount of substances like salt, lemon juice, or acid. These substances release ions in water, which help in the flow of electric current.

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: In case of a fire, firemen first switch off the main electrical supply because water is a good conductor of electricity. If water comes in contact with live wires, it can cause electric shocks to the firemen and others nearby. So, to prevent accidents and ensure safety, the electricity is turned off before using water hoses.

8. A child staying in a coastal region tests 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 explain the reason?

Answer: Seawater contains a larger amount of dissolved salts than drinking water. These salts produce more ions, which allow electric current to pass more easily. Hence, the current is stronger in seawater, causing a greater deflection in the compass needle.

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

Answer: No, it’s not safe for an electrician to do electrical repairs during a heavy downpour. Rainwater conducts electricity because it contains dissolved salts and impurities. If the electrician touches wet wires or equipment, electric current can pass through the water and cause a severe electric shock. So, repairs should only be done when it’s dry and safe.

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: Rainwater usually contains dissolved gases like carbon dioxide and impurities or dust particles from the atmosphere. These substances form ions when mixed with water, making it slightly conducting. That’s why, when Paheli tested the rainwater, electric current flowed through it, causing the compass needle to show deflection.

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

Answer: List of objects around us that are electroplated:

(i) Car parts like bumpers and handles

(ii) Bath taps and kitchen gas burners

(iii) Bicycle handlebars and wheel rims

(iv) Jewellery coated with silver or gold

(v) Tin cans used for storing food

(vi) Iron gates or automobile parts coated with zinc to prevent rusting

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 transfered to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

Answer:  The impure copper rod should be connected to the positive terminal of the battery because copper from the impure rod dissolves into the solution as positive copper ions. These ions then get deposited on the pure copper plate, which is connected to the negative terminal, forming pure copper. Thus, impurities stay behind, and the pure copper plate gets thicker.