Daily Olympiad: Science - Chemical Effects Electric Current [20260520]

Solution

Correct: B

Liquids conduct electricity due to the presence of free ions. When salts, acids, or bases dissolve in water, they dissociate into positive and negative ions, which can move and carry electric charge.

Solution

Correct: D

Distilled water is pure water without any dissolved salts or impurities, which means it lacks free ions to conduct electricity. Tap water, salt solution, and vinegar all contain dissolved substances that form ions, making them good conductors.

Solution

Correct: C

Electrolysis is a chemical process that uses electric current to drive non-spontaneous chemical reactions. It involves the decomposition of an electrolyte by passing an electric current through it.

Solution

Correct: C

Ions are atoms or molecules that have an electrical charge due to gaining or losing electrons. In liquids, these mobile ions are responsible for carrying the electric current.

Solution

Correct: C

The formation of gas bubbles at the electrodes (e.g., hydrogen and oxygen from water decomposition) is a clear sign of a chemical change brought about by the electric current. This is known as the chemical effect of electric current.

Solution

Correct: C

Electroplating is a specific application of the chemical effects of electric current where a thin layer of one metal is deposited onto the surface of another metal or object, usually for decorative purposes or to prevent corrosion.

Solution

Correct: C

Chromium plating provides a brilliant, shiny, and non-corrosive finish. It also makes the surface resistant to scratches, enhancing both the appearance and durability of the objects.

Solution

Correct: C

Lemon juice contains citric acid, which dissociates into ions in water, making it a good conductor of electricity. Kerosene, sugar solution (unless highly concentrated and heated to decompose sugar), and mustard oil are generally non-conductors or very poor conductors.

Solution

Correct: B

The object to be plated acts as the cathode. Positively charged metal ions from the electrolyte are attracted to the cathode, where they gain electrons and deposit as a metallic layer. Therefore, the object must be connected to the negative terminal of the battery.

Solution

Correct: C

An electrolyte is a substance (typically a liquid or solution) that contains free ions and thus conducts electricity. During electrolysis, the electric current passes through the electrolyte.

Solution

Correct: C

Tap water contains dissolved salts and impurities, making it a good conductor of electricity. If your hands are wet, electricity can easily pass through your body, leading to a dangerous electric shock.

Solution

Correct: C

Zinc is commonly electroplated on iron to prevent rusting, a process known as galvanization. Zinc is more reactive than iron and acts as a sacrificial layer, corroding instead of the iron.

Solution

Correct: D

Vinegar (acetic acid solution), common salt solution (sodium chloride), and dilute sulphuric acid all contain ions and are thus electrolytes. Pure glycerin is a molecular compound that does not dissociate into ions, making it a non-electrolyte.

Solution

Correct: B

If the anode is made of the metal that is being plated onto the cathode (e.g., a copper anode for copper plating), the anode itself dissolves into the electrolyte, providing the metal ions needed for deposition.

Solution

Correct: C

Extracting metals from their ores, often through processes like electrolytic reduction, is a direct application of the chemical effect of electric current, where electricity causes chemical decomposition to yield pure metal. Electric heaters use the heating effect, doorbells use the magnetic effect, and fans use the magnetic effect.