Science STD 8 Chapter 11: Chemical Effects of Electric Current - Exercises

The magnetic needle shows deflection because the solution acts as a conductor, allowing the electric current to pass through it. The passage of electric current produces a magnetic effect. Even a weak current can cause a deflection in the magnetic needle, indicating that the solution is conducting electricity.

Three liquids that may cause the magnetic needle to deflect are lemon juice, tap water, and vinegar. These liquids are good conductors of electricity due to the presence of dissolved acids or salts.

Possible reasons why the bulb does not glow in the given setup are:

• The liquid in the beaker might be a poor conductor of electricity. In this case, the current is too weak to heat the bulb's filament.
• The connections in the circuit might be loose.
• The bulb itself could be fused or damaged.
• The battery might be weak or used up.

1. liquid A is a better conductor than liquid B.
2. liquid B is a better conductor than liquid A.
3. both liquids are equally conducting.
4. conducting properties of liquid cannot be compared in this manner.

Pure water (distilled water) is a poor conductor of electricity because it is free of dissolved salts. To make it conducting, we can add a pinch of common salt, a few drops of an acid like lemon juice, or a base like caustic soda to it. The dissolved ions from these substances make the water a good conductor.

Firemen shut off the main electrical supply because the water they use to douse the fire is a good conductor of electricity due to the presence of dissolved mineral salts. If the electrical supply is not shut off, the water could conduct electricity and cause electric shock to the person trying to extinguish the fire. It could also damage the electrical equipment.

The compass needle deflects more in the case of seawater because it is a better conductor of electricity than drinking water. Seawater contains a much higher concentration of dissolved salts. These salts break down into ions in the water, which allows the electric current to flow more easily and strongly, resulting in a larger magnetic effect and a greater deflection of the compass needle.

No, it is not safe for an electrician to carry out electrical repairs outdoors during a heavy downpour. Rainwater is not pure water; it contains dissolved mineral salts, making it a conductor of electricity. There is a high risk of electric shock or short circuits if the electrician comes in contact with electrical wires while exposed to rain.

Paheli's observation is correct because rainwater is not as pure as distilled water. As rain falls through the atmosphere, it dissolves gases like carbon dioxide, sulphur dioxide, and nitrogen oxides, forming carbonic, sulphuric, and nitric acids. These impurities make rainwater a weak conductor of electricity, which is enough to cause a deflection in a sensitive compass needle.

A list of objects that are commonly electroplated includes:

• Car parts, such as bumpers and wheel rims.
• Bathroom taps and showerheads.
• Kitchen gas burners.
• Bicycle handlebars.
• Jewellery with a gold or silver coating.
• Tin cans used for storing food.

The thick rod of impure copper should be attached to the **positive terminal** of the battery. This is because, during electroplating, the impure copper dissolves into the solution from the positive electrode (anode). The copper ions from the solution then get attracted to the negative electrode (cathode) and get deposited as pure copper. This process continuously transfers pure copper from the impure rod to the thin plate.

Outline: This activity demonstrates that many fruits and vegetables can act as conductors due to the presence of acids and mineral salts. You would use a tester (like the one with a magnetic compass) to test fruits like lemon and oranges and vegetables like potatoes and tomatoes. The results would be presented in a table showing whether each item is a good or poor conductor. For example, a lemon would be a good conductor due to its high citric acid content.

Outline: This activity is a hands-on exploration of electroplating. By using a zinc plate and a copper sulphate solution, you would observe a layer of copper getting deposited on the zinc plate. This demonstrates that a less reactive metal can be coated with a layer of a more reactive metal. The discussion would focus on the principles of electroplating and how different metal combinations can be used to create specific coatings.

Outline: This project involves a field trip to an electroplating unit to understand industrial processes. You would learn that commercial units electroplate various objects like car parts, jewellery, and utensils for purposes like corrosion resistance, improving appearance, and increasing durability. You would also inquire about their waste disposal methods, highlighting the environmental concerns related to the chemicals used in electroplating.

Outline: This is a creative project that encourages you to apply your knowledge of electroplating in a business scenario. As an entrepreneur, you might choose to electroplate steel jewellery with a thin layer of gold to make it look expensive without being as costly as solid gold. This would attract customers who want affordable, stylish jewellery. You would also explain how you would manage waste to ensure an environmentally friendly operation.

Outline: This project is a research activity on the health hazards of chromium electroplating. You would learn that chromium compounds are toxic and can cause respiratory problems, skin rashes, and other health issues. The research would also reveal that people are trying to resolve these issues by using safer alternative coatings, implementing stricter waste disposal regulations, and improving safety measures in the workplace to minimise worker exposure to harmful chemicals.

Outline: This project is a creative demonstration of the chemical effects of electric current. When you write on the paste with the free end of the wire, the electric current causes a chemical reaction that produces a visible colour change. The potassium iodide reacts to form iodine, which then reacts with the starch to form a blue-black compound, making your writing visible. This shows how electricity can be used to cause a chemical change and create a fun, temporary "pen."