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Q1. Why distilled water is a poor conductor of electricity?

Solution

Distilled water is a poor conductor of electricity because it does not contain any dissolved salts in it which can provide it ions to conduct electricity.

Q2. Does pure water conduct electricity? If not, what can we do to make it conducting?

Solution

No, pure water does not conduct electricity. We can add a pinch of common salt in pure water to make it conducting.

Q3. How will you identify the positive terminal of a battery if it is hidden in a box and you can only see two of its leads.

Solution

Both the leads of the battery can be dipped into a single piece of potato for long time. After that, it can be observed that there is green coloration near one of the terminals. This is the positive terminal and the other one is the negative terminal.

Q4. Mention three common solutions that are good conductors of electric current. What is common in these solutions?

Solution

Good conductors are:1.    Common salt in water2.    Hydrochloric acid in water3.    Copper sulphate in waterThey all are solutions of acid, base or salt in water.

Q5. How will you modify an electroplating circuit to clearly indicate that the electroplating process is over?

Solution

An LED can be added to the circuit in the same way it is connected in a tester. While electroplating is still taking place, electric current will flow and the LED will be lighted up. The moment electroplating stops, so does the flow of current and thus the LED will also turn off.

Q6. If metal electrodes are coated with an insulator, what will happen during electroplating?

Solution

No electroplating will take place as insulators will not appear as positive or negative electrodes to the ions in the solution. For electroplating to take place, the surface on which metal is to be deposited should be a good conductor (whether bulk is conducting or not has no effect).

Q7. When the free ends of a magnetic tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Solution

The magnetic needle shows deflection due to the current passing through the wire wound around it. The current will pass only when the circuit is complete i.e. the when the solution allows electric current to pass through it. So, the magnetic needle deflects to show that the given solution is conducting in nature.

Q8. Mention the components in a circuit of a tester.

Solution

The components are:1. Battery2. Leads or wires3. Key4. Bulb/LED/magnetic compass

Q9. Define electroplating. List any three uses of it.

Solution

The method of coating one metal with another using an electric current is called electroplating. Uses: i) Metals that corrode easily can be protected by coating them with a metal that does not corrode easily. ii) An attractive and shiny appearance  is given to the objects made of iron or steel. iii) Ornaments made of a cheap metal are coated with a more expensive metal to make them look more attractive.

Q10. Can a solution, which is a poor conductor of electricity according to our testers, ever allow electric current to pass through it? Give a common example.

Solution

Yes, even if a solution seems to be a poor conductor of electric current, it might become a good conductor if a high voltage is applied on it. A common example is air, which is a poor conductor according to all the testers we might devise, but still allows lightning, which is electric current, to pass through it.

Q11. A child staying in a coastal region tests the drinking water and also the sea water with his tester. He finds that the compass needle deflects more in the case of sea water. Can you explain the reason?

Solution

Sea water contains more dissolved salts than drinking water, which makes it more conducting. Because of this reason, the compass needle deflects more in sea water than in drinking water.

Q12. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain

Solution

No, it is not at all safe for an electrician to carry out electrical repairs during heavy downpour. Rather, it is highly dangerous because during heavy downpour there is a high risk of electrocution as water is a good conductor of electricity.

Q13. Distilled water is a poor conductor of electric current. Then why should we never touch electrical appliances with wet hands?

Solution

Mostly our hands are wet with tap water and not distilled water. Tap water has salts dissolved in it and it is a good conductor of electric current. So we should never touch electrical appliances with wet hands.

Q14. How is electroplating used to save iron from corrosion?

Solution

Using the technique of electroplating, iron is coated with zinc which does not corrode.

Q15. What effects does an electric current produce when flowing through a conducting solution?

Solution

When an electric current flows through the conducting solution, it causes a chemical reaction (or chemical change).These chemical reactions may produce one or more of the following effects:i) Bubbles of gas (or gases) may be formed on the electrodes.ii) Deposits of metals may form on electrodes.iii) Change in colour of solution may occur.

Q16. Gold does not corrode. Despite this, gold ornaments start showing patches of other color after repeated use. Why?

Solution

Most ornaments that appear to be made of gold are actually made of other metal and only coated with gold. After repeated use, the gold layer tends to peel off in patches and the metal underneath, which is of a different color starts to show.

Q17. What is an electrolyte? Give one example.

Solution

A liquid that conducts electricity because of the presence of the ions is called an electrolyte. Example: a solution of copper sulphate salt in water.

Q18. In what way does adding an impurity like salt affect the conductivity of pure water?

Solution

Pure water does not form enough ions to conduct electricity that is why pure water is a poor conductor of electricity. By adding salt, it forms ions of sodium and chloride which makes it possible for an electric current to pass through the solution.

Q19. During electroplating, initially some bubbles were appearing near an electrode. After 30 mins, no bubbles appear. What do you conclude from this?

Solution

If bubbles have stopped, this means that no chemical effects are taking place in the solution any more. Thus, there must not be any electrical conduction occuring in the solution which implies that electroplating was taking place initially but has now stopped.

Q20. Define (i) Electrolyte (ii) Cathode (iii) Anode

Solution

(i) Electrolyte: A liquid that conducts electricity due to the presence of ions is called an electrolyte. (ii) Cathode: The electrode connected to the negative terminal of the battery is called cathode. (iii) Anode: The electrode connected to the positive terminal of the battery is called anode.

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