Q1. In testing the electrical conductivity of liquids, what is the advantage of using LED over bulb? Choose the wrong option.
Solution
If a weak current flows through the circuit, the heating effect produced by the current in the filament of the bulb through the circuit will be weak. Hence, the filament of the bulb does not get heated sufficiently and the glow of the bulb is weaker. Therefore, a LED is used in place of a bulb.
Q2. Mention any two applications of electrolysis.
Solution
Applications of electrolysis:(i) Used in the production of many metals and non metals, such as aluminum, magnesium, chlorine.(ii) Used for coating one metal with another.
Q3. A chemical change in a solution can be identified by
Solution
In a chemical change all of the above mentioned effects might occur.
Q4. Which of the following is not a strong electrolyte?
Solution
Acetic acid solution is a weak conductor of electricity.
Q5. When the liquid between two ends of a tester is a good conductor, the bulb glows because
Solution
A conducting liquid allows electric current to pass through it and hence completes the circuit. This makes the bulb connected in the circuit glow.
Q6. Instead of a bulb, sometimes a LED is used in the tester, because
Solution
LED glows even with weak currents but bulbs do not. So, a LED is sometimes used in the circuit to detect weak currents passing through weak electrolytes.
Q7. 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.
Q8. 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.
Q9. When an electric current flows through a solution, it produces
Solution
Chemical effects in the solution are produced when an electric current flows through a solution.
Q10. 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.
Q11. 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.
Q12. A metal is released in the electrolysis of a salt. It gets deposited on the
Solution
A metal is released in the electrolysis of a salt. It gets deposited on the cathode.
Q13. The bulb does not glow in the setup shown in Figure. List the possible reasons. Explain your answer.
Solution
The bulb may not glow because of the following reasons: (i) Liquid in the beaker may be non-conducting. In such a case, the electric current would not be able to pass through the liquid. Hence, the circuit will not be complete. (ii) The conductivity of the liquid may be very low and so the current flowing through the circuit may be too weak to produce enough heat in the filament of the bulb so as to make it glow. (iii) The battery may be exhausted and does not have sufficient energy to generate electricity. (iv) The bulb may be fuse or the circuit connections may be loose.
Q14. 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.
Q15. 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).
Q16. _________ is one of the chemical effects of electric current.
Solution
Electroplating is one of the chemical effects of electric current.
Q17. 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.
Q18. 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.
Q19. Substances which allow electricity to pass through them are called ___________.
Solution
Substances which allow electricity to pass through them are called conductors.
Q20. Substances which do not allow electric current to pass through them are called _________.
Solution
Substances which do not allow electric current to pass through them are called insulators.
Q21. How is electroplating used to save iron from corrosion?
Solution
Using the technique of electroplating, iron is coated with zinc which does not corrode.
Q22. 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.