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

Question: In case of a fire, before the fireman uses the water hoses to throw water to douse fire, they shut off the electricity supply for the area. Explain why this is done?

Answer: To prevent electrocution of fireman because ordinary water is conductor of electricity.

Question: When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into a solution, the magnetic needle shows deflection. Can you give the reason of this deflection?

Answer: Electric current flowing through the wire produces a magnetic field around it. And this magnetic field of electric current acts on the magnetic needle of compass; deflects it.

Question: What effects does an electric current produce when flowing through a conducting solution?

Answer: When an electric current flows through the conducting solution, it causes a chemical reaction (or chemical change). These chemical reactions may produce following effects:

1. Bubbles of gas/es may be formed on the electrodes.
2. Deposits of metals may form on electrodes.
3. Change in colour of solution may occur.

Question: When electric current is passed through acidified water then what is produced at a) Positive carbon electrode (anode)? b) Negative carbon electrode (cathode)?

Answer: a) oxygen gas b) hydrogen gas.

Question: Which effect of electric current is utilized when a thin layer of chromium metal is deposited on an iron tap? What is this process known as?

Answer: Chemical effect of current is utilized. The process is known as electroplating.

Question: What is meant by electroplating? What is the purpose of electroplating?

Answer: The process of depositing a layer of any desired metal on another material, by means of electricity, is called electroplating. Electroplating is done:

1. for protection against corrosion (or rusting).
2. for decorative purposes.

Question: Which properties of chromium metal make it suitable for electroplating it on car bumpers, bath taps & bicycle hand bars, etc., made of iron?

Answer: It has shiny appearance. It does not corrode easily. It resists scratches.

Question: Which metal is electroplated on iron for making ‘cans’ used for storing food & Why?

Answer: Tin is used to electroplate iron for making cans useful for storing food. Tin metal has shiny appearance, it does not corrode & it is non poisonous.Tin is less reactive than iron. Due to tin plating over the surface of iron, the food does not come in contact with iron & is protected from getting spoilt.