GSEB Class 8 Science Solutions Chapter 14 Chemical Effects of Electric Current

Question 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 sulfate 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) acids, bases, salts
(b) chemical
(c) negative
(d) electroplating.
In simple words: Many liquids that allow electricity to pass through them are solutions of either acids, bases, or salts. When electricity goes through a liquid solution, it makes chemical changes happen. In a copper sulfate solution, copper sticks to the plate linked to the battery's negative side. Using electricity to put a thin layer of one metal onto another material is known as electroplating.

Exam Tip: Remember the basic components of conducting liquids (acids, bases, salts) and the primary effect of current passing through solutions (chemical effects). For electroplating, linking it to the negative terminal ensures metal deposition.

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: Yes, we can explain the reason. The magnetic needle will show deflection when the circuit becomes complete. The deflection of the magnetic needle indicates that the solution is a good electrical conductor.
In simple words: A magnetic needle moves when the circuit is complete and electricity flows. This movement shows that the liquid is letting electricity pass through it, meaning it is a good conductor.

Exam Tip: The key principle here is that a magnetic needle detects current flow. Its deflection confirms that the circuit is closed and the liquid is conducting electricity, causing a magnetic field.

Question 3. Name three liquids, which when tested in the manner shown in Fig. 14.1 may cause the magnetic needle to deflect.
Answer: Tap water, hydrochloric acid, sodium hydroxide.
In simple words: Some liquids that can make the magnetic needle move are ordinary tap water, a strong acid called hydrochloric acid, and a strong base called sodium hydroxide.

Exam Tip: Recall common household liquids and strong laboratory solutions that act as good electrolytes, containing ions that allow electric current to flow.

Question 4. The bulb does not glow in the set up shown in Fig. 14.2. List the possible reasons. Explain your answer.
Answer: The possible reasons may be:
• The connections of the circuit may be loose.
• The bulb may be fused.
• The cells may be used up.
• The liquid may be a poor conductor.
In simple words: If the bulb does not light up, it could be because the wires are not connected tightly, the bulb itself is broken, the battery has no power left, or the liquid in the setup does not let electricity pass through it easily.

Exam Tip: When troubleshooting a non-working circuit, systematically check all components: power source, connections, load (bulb), and the medium (liquid) for conductivity.

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:
(a) liquid A is a better conductor than liquid B.
(b) liquid B is a better conductor than liquid A.
(c) both liquids are equally conducting.
(d) conducting properties of liquid cannot be compared in this manner.
Answer: (a) liquid A is a better conductor than liquid B.
In simple words: When the bulb glows brightly, it means more electricity is flowing. A dim glow means less electricity. So, if liquid A makes the bulb shine brighter, it lets electricity pass through better than liquid B.

Exam Tip: The brightness of the bulb in a tester directly relates to the conductivity of the liquid. A brighter glow indicates higher conductivity, while a dimmer glow suggests lower conductivity.

Question 6. Does pure water conduct electricity? If not what can we do to make it conducting?
Answer: No, pure water does not conduct electricity. Pure water can be made conducting by dissolving salt in it.
In simple words: Clean, pure water does not carry electricity. To make it conduct electricity, we can mix some salt into it. The salt adds particles that help electricity move.

Exam Tip: Pure water is a poor conductor because it lacks free ions. Adding impurities like salts (electrolytes) introduces ions, making it a good conductor. This is why tap water conducts electricity but distilled water does not.

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: The water used in water hoses is a good conductor of electricity. Firemen turn off the main electrical supply, because if the electricity continues there may be a high risk of electrocution due to the water.
In simple words: Firemen switch off the electricity before using water because the water they use can carry electric current. This prevents people from getting an electric shock, which is very dangerous.

Exam Tip: Water, especially tap water or river water, contains dissolved salts that make it conductive. Mixing water with active electrical circuits creates a serious hazard, hence the safety protocol of cutting power first.

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 explain the reason?
Answer: Seawater contains a greater amount of salt than drinking water. So, the seawater is a better conductor of electricity. This is the reason that the compass needle deflects more in the case of seawater.
In simple words: Seawater has much more salt than regular drinking water. More salt means more particles that can carry electricity, so seawater lets electricity pass through more easily. This strong flow of electricity causes the compass needle to move a lot more.

Exam Tip: The concentration of dissolved salts (ions) directly affects the conductivity of water. Seawater, with its high salinity, is an excellent conductor compared to drinking water, leading to a stronger magnetic effect on the compass needle.

Question 9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Answer: No, it is not safe for the electrician to carry out electrical repairs outdoors during a heavy downpour. It is because during heavy downpour there is a higher risk of electrocution.
In simple words: It is not safe for electricians to fix electrical things outside when it's raining heavily. Rainwater can conduct electricity, which means there is a very high chance of getting an electric shock.

Exam Tip: Water significantly increases the risk of electrocution as it acts as a conductor, providing a path for electricity to flow through the body. Always avoid electrical work in wet conditions.

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: Rainwater is like distilled water but some impurities get mixed in from the atmosphere. These impurities make the rainwater conducting. This could be the reason for the deflection of the compass needle.
In simple words: Even though rainwater starts pure, it picks up dirt and other bits from the air as it falls. These extra bits turn the rainwater into something that can carry electricity, making the compass needle move.

Exam Tip: While rain starts as distilled water, it collects atmospheric pollutants and dust, dissolving them to form a weak electrolyte solution. This makes it slightly conductive, sufficient to cause a compass needle to deflect.

Question 11. Prepare a list of objects around you that are electroplated.
Answer: Pots of metals, bath taps, ornaments, rims of vehicles, the handlebar of cycles and motorcycles, kitchen gas burner, the bottom of cooking utensils, handles of doors, tin cans are some objects around us that are electroplated.
In simple words: Many items around us are coated with a thin layer of another metal using electricity. This includes metal pots, bathroom taps, jewelry, car wheel rims, bicycle handles, gas stove parts, bases of cooking pans, door handles, and tin cans.

Exam Tip: Electroplating is widely used for enhancing appearance, preventing corrosion, and increasing durability. Think of objects that need to look shiny, resist rust, or be stronger.

Question 12. The process that you saw in Activity 14.7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the 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 rod of the copper plate should be connected to the positive terminal of the battery. Because when an electric current is passed through the copper sulfate solution, it separates into copper and sulfate particles. The free copper drawn to the negative terminal of the battery gets deposited on it. On the other hand, the loss of copper from the solution would be gained from the impure copper rod which is connected to the positive terminal of the battery.
In simple words: The impure copper rod should go to the positive side of the battery. When electricity passes, copper from the impure rod dissolves into the solution and then moves to the pure copper plate on the negative side, making it thicker and purer.

Exam Tip: In electrolytic refining, the impure metal acts as the anode (positive terminal) where it oxidizes and dissolves into ions, while the pure metal acts as the cathode (negative terminal) where the pure metal ions deposit.