NCERT 8th Class (CBSE) Science: Chemical Effects of Electric Current

Question: Why the bulb glows when the electric current passes through it?

Answer: Due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing.

Question: Does distilled water conduct electricity? Or, Does pure water conduct electricity? If not, what can we do to make it conducting?

Answer: No. distilled [pure] water does not conduct electricity When salt is dissolved in distilled water, we obtain salt solution. This is a conductor of electricity.

Question: Is tap water good conductor or bad conductor?

Answer: Tap water is good conductor because of the number of gases and mineral mixed into it.

Question: What is electrolysis?

Answer: The process of causing a chemical change in a solution by passing electricity is called electrolysis. This process is discovered by Johann Wilhelm. During electrolysis Cation gets reduced at Cathode and anion gets oxidized at anode.

Question: What is electrolyte?

Answer: The solution which contain electrode and conducts the current through itself is called electrolyte. Or, A substance which conduct electricity when dissolve in water or when melted is called electrolyte. Or. A substance which gives ion when melted or dissolves in water is called electrolyte.

Question: What phenomenon may occur during electrolysis?

Answer: At least one of the phenomenons may occur during electrolysis:

1. Deposition of gas bubbles on elected.
2. Change in the colour of electrolyte solution.
3. Deposition of metal on cathode

Question: Write some application of electrolysis?

Answer: The principal of electrolysis is used:

1. Purifying impure metal into pure one [called Refining]
2. Extraction of metal from their ores [called metallurgy]
3. Manufacture of industrial chemicals.
4. Electroplating

Question: In case of a fire, before the firemen use the water hoses, they shut off the main electrical
supply for the area. Explain why they do this.

Answer: This is because potable water is good conductor of electricity.

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

Answer: This is because seawater contains more salt and impurities than drinking water and a strong electrolyte.

Question: Define electroplating?

Answer: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. During electroplating, the object to be electroplated is made cathode and A thin plate of metal to be electroplated is made anode. A solution of any suitable salt of metal to be electroplated is used as electrolytes.