Class 8 Science
Chemical Effects of Electric Current – Notes + Practice Questions
1. Conduction of Electricity in Liquids
Electric current can pass through some liquids just like it passes through wires.
Examples of conducting liquids
Lemon juice, Salt water, Tap water, Acid solutions, Non-conducting liquids, Distilled water, Kerosene, Oil
Key Point:
Liquids that allow electric current to pass through them are called conductors, while those that do not allow current are insulators.
Practice Questions:
1. Name two liquids that conduct electricity.
2. Why does distilled water not conduct electricity?
3. What happens when salt is added to distilled water?
2. Chemical Effects of Electric Current
When electric current passes through a conducting liquid, chemical reactions may occur.
These reactions may cause:
i) Formation of bubbles of gas.
ii) Deposits of metal on electrodes.
iii) Change in colour of the solution.
This phenomenon is called Chemical Effect of Electric Current.
Practice Questions:
1. What is meant by chemical effect of electric current?
2. Name two changes that indicate chemical effects.
3. Give one example of chemical effect in daily life.
3. Electrodes
The two terminals of a battery connected to a liquid are called electrodes.
Types:
i) Positive Electrode (Anode). ii) Negative Electrode (Cathode)
Electrodes are usually made of graphite or metal strips.
Practice Questions:
1. What are electrodes?
2. Name the two types of electrodes.
3. Which electrode is connected to the positive terminal?
4. Electroplating
Electroplating is the process of depositing a thin layer of one metal on another using electric current.
Example:
i) Gold plating on jewellery.
ii) Chromium plating on taps and car parts.
Why Electroplating is Done?
1. To prevent rusting
2. To improve appearance
3. To increase durability
Practice Questions:
1. What is electroplating?
2. Name one metal used for plating taps.
3. Why are iron objects electroplated with chromium?
5. Applications of Electroplating
Electroplating is used in many industries.
Examples:
i) Jewellery making
ii) Car parts coating
iii) Tin-plated food cans
iv) Bicycle handle plating
Practice Questions:
1. Write two uses of electroplating.
2. Why are food cans coated with tin?
3. Name one object in your house that is electroplated.
6. Good Conductors and Poor Conductors:
Some liquids conduct electricity better than others.
Good Conductors:
i) Acid solutions. ii) Salt solutions
Poor Conductors:
i) Distilled water. ii) Sugar solution
Practice Questions:
1. Which solution conducts electricity better: sugar solution or salt solution?
2. Why is tap water a conductor?
3. Define good conductor.
Very Short Answer:
1. Define electroplating.
2. What are electrodes?
3. Name one liquid conductor.
4. What happens when current passes through a liquid?
5. Give one use of electroplating.
Short Answer Questions:
1. Explain chemical effects of electric current.
2. Write differences between conductors and insulators.
3. Why is chromium used for electroplating taps?
4. Explain electroplating with an example.
Long Answer Questions:
1. Describe the process of electroplating with a diagram.
2. Explain the chemical effects produced by electric current in liquids.
3. Write the advantages of electroplating.
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