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 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 __________.

Accepted 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. — Liquids that conduct electricity typically contain ions, which are present in solutions of acids, bases, and salts. When electric current passes through such solutions, chemical changes occur (chemical effects). In copper sulphate solution electrolysis, copper ions move towards the cathode (negative terminal) and get deposited there. Electroplating is the process of depositing a metal layer on another material using electric current.

Question 2

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

Accepted Answer

The magnetic needle shows deflection because the solution conducts electricity, allowing current to flow through the circuit. The current produces a magnetic field around the wire, which causes the magnetic needle to deflect. — When the tester's free ends are dipped into a conducting solution, ions in the solution carry electric current. The current flowing through the wire creates a magnetic field, which interacts with the magnetic needle causing it to deflect. This indicates the solution is a conductor of electricity.

Question 3

Name three liquids, which when tested in the manner shown in Fig.11.9, may cause the magnetic needle to deflect.

Accepted Answer

Three liquids that may cause the magnetic needle to deflect are:
1. Salt water (solution of common salt in water)
2. Lemon juice (acidic solution)
3. Vinegar (acetic acid solution) — These liquids contain ions which can conduct electricity. When the tester is dipped into these liquids, current flows through the circuit, producing a magnetic field that deflects the magnetic needle as shown in Fig. 11.9.

Question 4

The bulb does not glow in the setup shown in Fig.11.10. List the possible reasons. Explain your answer.

Accepted Answer

Possible reasons why the bulb does not glow:
1. The liquid in the container may not be conducting electricity (e.g., pure water).
2. There may be a loose connection or break in the circuit.
3. The bulb may be fused or faulty.
4. The battery may be dead or not connected properly.

Explanation: For the bulb to glow, the circuit must be complete and the liquid must conduct electricity to allow current flow. If any of these conditions fail, the bulb will not glow. — The bulb glows only if current flows through the circuit. If the liquid is non-conducting, no current flows. Similarly, loose connections or faulty components prevent current flow, causing the bulb to remain off.

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.

Accepted Answer

Option (i) liquid A is a better conductor than liquid B.

Explanation: The brightness of the bulb depends on the amount of current flowing through the circuit. A brighter bulb indicates higher current, which means liquid A conducts electricity better than liquid B. — Since the bulb glows brightly with liquid A and dimly with liquid B, it shows that liquid A allows more current to pass through, indicating better conductivity.

Question 6

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

Accepted Answer

Pure water does not conduct electricity because it lacks free ions. To make it conducting, we can add a small amount of an electrolyte such as salt, acid, or base to produce ions that carry electric current. — Pure water is a poor conductor as it contains very few ions. Adding substances like salt dissociates into ions, enabling the solution to conduct electricity.

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.

Accepted Answer

Firemen shut off the main electrical supply before using water hoses because water conducts electricity. If the electrical supply is not turned off, water can conduct electricity and cause electric shocks, posing danger to the firemen. — Water is a conductor of electricity when it contains impurities. Using water near live electrical circuits can cause electric shocks. To ensure safety, electrical supply is switched off before water is used.

Question 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?

Accepted Answer

Seawater contains more dissolved salts (ions) than drinking water. These ions increase the conductivity of seawater, allowing more current to flow, which causes greater deflection of the compass needle. — The presence of dissolved salts in seawater provides more charge carriers (ions), resulting in better conduction of electricity compared to drinking water, hence the larger deflection.

Question 9

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

Accepted Answer

It is not safe for an electrician to carry out electrical repairs outdoors during heavy rain because water conducts electricity and increases the risk of electric shock. — Water on the ground and equipment can create a conductive path for electricity, increasing the danger of electrocution. Hence, repairs should be avoided during heavy rain for safety.

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?

Accepted Answer

Rainwater is not as pure as distilled water because it contains dissolved gases and impurities from the atmosphere, such as dust and smoke particles. These impurities ionize the water, making it slightly conductive, which causes the compass needle to deflect. — Distilled water is pure and does not conduct electricity well. Rainwater picks up impurities and dissolved gases as it falls, which provide ions that conduct electricity, explaining the deflection.

Question 11

Prepare a list of objects around you that are electroplated.

Accepted Answer

Common electroplated objects include:
- Jewellery (silver or gold plated)
- Cutlery (silver or stainless steel plated)
- Car bumpers and parts (chrome plated)
- Watches and clocks
- Coins
- Electrical connectors and pins
- Bathroom fittings (chrome plated taps and faucets) — Electroplating is used to coat objects with a thin layer of metal to improve appearance, prevent corrosion, or reduce friction. Many everyday items are electroplated for these reasons.

Question 12

The process that you saw in Activity 11.7 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?

Accepted Answer

The thick rod of impure copper should be attached to the positive terminal of the battery (anode), and the thin plate of pure copper should be attached to the negative terminal (cathode). This is because copper atoms from the impure anode dissolve into the solution and get deposited on the cathode as pure copper. — In electrorefining, the impure copper anode loses copper ions to the solution, which migrate and deposit on the cathode as pure copper, thus purifying the metal.

Question 13

Test the conduction of electricity through various fruits and vegetables. Display your result in a tabular form.

Accepted Answer

Students should test different fruits and vegetables using a tester and record whether the bulb glows or the magnetic needle deflects, indicating conduction. The results can be tabulated as:

| Fruit/Vegetable | Conducts Electricity (Yes/No) |
|-----------------|-------------------------------|
| Lemon           | Yes                           |
| Potato          | Yes                           |
| Apple           | Yes                           |
| Cucumber        | Yes                           |
| Carrot          | Yes                           |

Explanation: Fruits and vegetables contain water and electrolytes (salts and acids) which conduct electricity. — The presence of electrolytes in fruits and vegetables allows them to conduct electricity, which can be demonstrated by the tester.

Question 14

Repeat Activity 11.7 with a zinc plate in place of the copper plate connected to the negative terminal of the battery. Now replace zinc plate with some other metallic object and again repeat the activity. Which metal gets deposited over which other metal? Discuss your findings with your friends.

Accepted Answer

When a zinc plate is connected to the negative terminal and immersed in a suitable electrolyte, zinc metal gets deposited on the cathode. Replacing the zinc plate with other metals will show deposition depending on the electrolyte and metal used. Generally, metal ions from the anode dissolve and deposit on the cathode. Students should observe and discuss which metals deposit on others based on their experiments. — Electroplating depends on the metal ions in the solution and the electrodes used. Metals with higher reduction potential tend to deposit on the cathode.

Question 15

Find out if there is a commercial electroplating unit in your town. What objects are electroplated there and for what purpose? (The process of electroplating in a commercial unit is much more complex than what we did in Activity 11.7). Find out how they dispose off the chemicals they discard.

Accepted Answer

Students should research locally to find commercial electroplating units. Commonly electroplated objects include jewellery, car parts, and household items. The purpose is to improve appearance, prevent corrosion, and increase durability. They should also inquire about chemical disposal methods, which ideally involve proper treatment to prevent environmental pollution. — Commercial electroplating involves complex processes and chemical management. Proper disposal is important to avoid environmental hazards.

CHEMICAL EFFECTS OF ELECTRIC CURRENT

CHEMICAL EFFECTS OF ELECTRIC CURRENT — Study Notes

Introduction

Chemical Effects of Electric Current

Electroplating

Practice Questions — CHEMICAL EFFECTS OF ELECTRIC CURRENT

All 13 Chapters in Science