Saturday 28 October 2017

CBSE Class 8 Science - Chemical Effects of Electric Current (Q and A) (#cbseNotes)

Chemical Effects of Electric Current (Q and A)

CBSE Class 8 Science - Chemical Effects of Electric Current (Q and A) (#cbseNotes)

Q1: Which of the following liquids conduct electricity & which do not conduct electricity?
Lemon juice, Milk, Vinegar, Salt solution, Distilled water, Honey, Seawater, Rainwater.

Conducting: Lemon juice, Vinegar, Salt solution, sea water, Rainwater
Non-Conducting: Milk, Distilled water, Honey.

Q2: What is an electric current?

Answer: The rate of the flow of charge is called an electric current.

Q3: Name a device which glows even when a weak electric current passes through it.

Answer: LED (Light Emitting Diode)

Q4: When an electric current is passed through a solution of a metal salt. At which electrode the metal will be deposited?

Answer: At cathode.

Q5: What is the advantage of using LED over bulb in testing the electrical conductivity of liquids?

Answer: When electric current flows through a bulb then due to the heating effect of current, the filament of the bulb gets heated up to a high temperature and it starts glowing. For liquids having low electrical conductivity, the current flowing through the circuit is very weak due to which the filament does not get heated sufficiently. Thus the bulb
does not glow.

Therefore, LED is used in place of bulb because LED glows even when weak electric current flows in the circuit.

Q6: Distilled water does not conduct electricity. What substances can be added to distilled water in small amounts to make it a good conductor of electricity?

Answer: Salt, acid or base.

Q7: What is an electrolyte?

Answer: A substance which conducts electricity in the liquid state or when dissolved in water and breaks up chemically during the process is called an electrolyte.

Q8: Why is zinc electroplated on iron?

Answer: Zinc is electroplated on the iron to prevent it from rusting.

Q9: Why are metals good conductor of electricity?

Answer: Metals have a pool of free electrons which help in conducting electricity.

Q10: What are the advantages of electroplating iron with chromium?

Answer: Chromium is a shiny metal that does not corrode and resists scratches. It makes iron look more attractive and also resist corrosion.

Q11: How is electronic current different from conventional current?

Answer: The flow of electronic current is from negative to positive terminal whereas the flow of conventional current is from positive to negative terminal.

Q12: What happens when electricity is passed through tap water?

Answer: Tap water will conduct electricity as it has some salts dissolved in it. The electric current will break up tap water into its constituent gases, hydrogen and oxygen.

Q13: Which effect of electric current is utilized for detecting the flow of current through a solution:
(a) When a torch bulb is used?
(b) When a magnetic compass is used?

a) Heating effect
b) Magnetic effect.

Q14: 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.

Q15: Write down the important points which should be remembered while electroplating?

The metal on which electroplating is to be done should be cathode i.e., the negative electrode.

The metal to be deposited should be anode i.e., the positive electrode.

A water-soluble salt of the ‘metal to be deposited’ is taken as the electrolyte.

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