The DAV Class 8 Science Solutions and DAV Class 8 Science Chapter 16 Question Answer – Electric Current and Its Chemical Effects are essential study tools for DAV public school students in Class 8.
DAV Class 8 Science Ch 16 Question Answer – Electric Current and Its Chemical Effects
DAV Class 8 Science Ch 16 Solutions – Electric Current and Its Chemical Effects
Something To Know
A. Fill in the following blanks:
1. Most liquids, that conduct electricity, are solutions of ________, ________ and ________ .
Answer:
acid, base, salt
2. The ________ the concentration of an ion in the solution, the greater is the conductivity of the solution.
Answer:
greater
3. The passage of an electric current, through a solution, can cause ________ effects.
Answer:
chemical
4. When electric current is passed through copper sulphate solution, copper gets deposited on the plate connected to the ________ terminal of the battery.
Answer:
negative terminal
5. The process, in which electricity is used to deposit a thin layer of any desired metal on another metallic object, is known as ________ .
Answer:
electroplating
6. The faster is the relative motion between the magnet and the (closed) coil, the ________ is the current that flows through the coil.
Answer:
stronger
B. State true or false for the following statements:
1. A solution of silver nitrate is a good electrolyte.
Answer:
True
2. An electrolytic cell consists of a cathode, anode and an electrolyte.
Answer:
True
3. Oxygen gets liberated at the anode during the electrolysis of acidified water.
Answer:
True
4. Electrorefining is the process of coating one metal on another using an electric current.
Answer:
False
5. The phenomenon of ‘Electro-magnetic Induction’ was discovered by the Italian scientist, Alessandro Volta.
Answer:
False
C. Tick (✓) the correct option:
Question 1.
The names of four electrolytes are given below:
(A) Sea water
(B) Tap water
(C) Nitric acid
(D) Oxalic acid
Out of these, the weak electrolytes are the ones labelled as-
(a) A and B
(b) B and D
(c) B and C
(d) A and D
Answer:
(b) B and D
Question 2.
Electrolytes conduct electricity due to the movement of-
(a) The electrolyte itself
(b) Electrons only
(c) Positive as well as negative ions
(d) The electrodes themselves
Answer:
(c) Positive as well as negative ions
Question 3.
The electrode, connected to the positive terminal of a battery, is known as the-
(a) Anode
(b) Positive pole
(c) Cathode
(d) Electrorefiner
Answer:
(a) Anode
Question 4.
The phenomenon of decomposition of an electrolyte, when electricity is passed through it, is known as-
(a) Conduction
(b) Coating
(c) Electrolysis
(d) Electrorefining
Answer:
(c) Electrolysis
Question 5.
The process, of coating of (say) iron with chromium, is known as-
(a) Extraction
(b) Electrolysis
(c) Electroplating
(d) Electrorefining
Answer:
(c) Electroplating
D. Answer the following questions in brief:
Question 1.
State the appropriate term, used for a liquid or solution, which can conduct electricity (along with some accompanying chemical changes).
Answer:
Electrolyte
Question 2.
Distinguish between strong and weak electrolytes. Give two examples of each.
Answer:
Strong electrolyte completely dissociates into its ions in a solution, while a weak electrolyte incompletely dissociates into its ions in a solution. Nitric acid and sulphuric acid are strong electrolytes. Tap water and oxalic acid are weak electrolytes.
Question 3.
Name the device that converts-
(a) Chemical energy into electrical energy
(b) Mechanical energy into electrical energy
Answer:
(a) Cell
(b) Generator
Question 4.
Name the scientists who introduced the (scientific) world to the
(a) Voltaic cell
(b) Phenomenon of electrolysis
(c) Phenomenon of electro-magnetic induction
Answer:
(a) Alessandro Volta
(b) Alessandro Volta
(c) Michael Faraday
Question 5.
An electrode ‘A’ is connected to the positive terminal while electrode ‘B’ is connected to the negative terminal of a battery, as shown in the diagram.
(a) Give the names of the electrodes A and B.
(b) Name the process associated with the circuit shown here.
(c) Name the gases produced at A and B.
Answer:
(a) A is anode and B is cathode
(b) Electrolysis
(c) Oxygen at A and Hydrogen at B
Question 6.
State the meaning of the terms:
(a) Electro-magnetic induction
(b) Electrolysis
(c) Electrodes
(d) Electrorefining of metals
Answer:
(a) The production of electricity by a changing magnetic field is called electromagnetic induction.
(b) The chemical change in an ionic solution by passing electric current is called electrolysis.
(c) A metal rod/plate through which electric current enters or leaves an electric cell is called electrode.
(d) Obtaining pure metal from impure metal by electrolysis is called electrorefining of metals.
Question 7.
State three uses of the phenomenon of electrolysis.
Answer:
Following are the three uses of electrolysis:
- Electrorefining of metals
- Electroplating
- Extraction of metals
E. Answer the following questions:
Question 1.
Give reasons for the following:
(a) Solid sodium chloride does not conduct electricity while sodium chloride solution conducts.
(b) It is not safe to carry out electrical repairs outdoors during a heavy downpour.
(c) To carry out electrolysis of water, a few drops of sulphuric acid are (carefully) added to the water.
(d) Kitchen gas burners are often coated with chromium.
Answer:
(a) Solid sodium chloride does not provide free ions, while its solution provides free ions. Hence, solid sodium chloride does not conduct electricity while its solution conducts electricity.
(b) Rainwater often contains many dissolved salts in it. So, rainwater is a good conductor of electricity. Hence, carrying out electric repairs during a heavy downpour poses the risk of electric shock. So, it is not safe to carry out electric repairs during a heavy downpour.
(c) Adding a few drops of sulphuric acid makes the water more conducting. So, a few drops of sulphuric acid are added to water while carrying out electrolysis of water.
(d) The coat of chromium prevents corrosion of the gas burner. Hence, kitchen gas burners are often coated with chromium.
Question 2.
Three electrolytic cells A, B and C are connected with identical bulbs in separate circuits as shown in the diagram. Electrolytic cell A contains sodium chloride solution and electrolytic cell B contains acetic acid solution. The electrolytic cell C contains water.
(a) In which set-up will the bulb glow the brightest?
(b) In which setup will the glow of the bulb be quite dim?
(c) In which set-up will the bulb not glow at all?
Answer:
(a) Set-up A, because sodium chloride is a strong electrolyte.
(b) Set-up B, because acetic acid is a weak electrolyte.
(c) Set-up C, because distilled water is a bad conductor of electricity.
Question 3.
Ramit sets-up the circuit as shown below for purification of copper.
(a) Name the metals used for electrodes A and B.
(b) Name the process of purification.
(c) Name the solution that needs to be used.
Answer:
(a) Pure copper for electrode B and impure copper for electrode A
(b) Electrorefining
(c) Copper sulphate
Question 4.
(a) Define ‘electroplating’! How can steel spoons be plated with silver? Explain with the help of a diagram.
(b) State any three uses of electroplating.
Answer:
Coating a layer of metal on another metal by electrolysis is called electroplating.
- For this, a plate of pure silver is made the anode, while the steel spoon is made the cathode.
- Silver nitrate is used as electrolyte.
- When electric current flows through the set up, pure silver from anode dissociates and gets deposited on cathode. Thus, a coat of silver is applied on the spoon.
Question 5.
Describe an experiment to show that we can get electrical energy by using a magnet.
Answer:
Take a hollow cylindrical pipe of iron, some copper wires, bulb and a bar magnet.
- Wrap numerous turns of copper wire over iron cylinder.
- Connect the wires to a bulb.
- Move the bar magnet towards the coil. You will notice that the bulb glows.
- Now, move the bar magnet away from the coil. You will notice that the bulb glows.
- This shows that we can get electrical energy by using a magnet.
Question 6.
A coil of insulated copper wire is connected to a torch bulb. State the likely ‘response’ of the bulb, if a bar magnet is
(a) Pushed into the coil?
(b) Pullcd out of the coil?
(c) Held stationery within the coil?
Answer:
(a) Bulb glows
(b) Bulb glows
(c) Bulb does not glow
Value Based Question
One day, when Aisha came back from school, she was very upset and was on the verge of crying. When her mother consoled her, Aisha vent out her feelings to her and told her that she was bullied by seniors at her school. Her mother calmed her and advised her to learn to face such challenges. She gave her the example of electroplating, in which a protective cum decorative layer is put over a base metal to help it avoid corrosion. She told Aisha that we all need to develop a ‘shield of courage’ around us. This would help us in protecting ourselves from negative influences and in ‘freeing us from fear’. Aisha resolved to follow her mother’s advice and felt better equipped to face all types of challenges.
Question 1.
State the values depicted by Aisha’s mother.
Answer:
Courage to face the challenges
Question 2.
State any three conditions that help in getting smooth and firm deposit during electroplating.
Answer:
Source of electric current, suitable electrolyte and anode of pure metal.
Question 3.
Have a ‘group discussion’ about developing qualities that can help one to face the ‘day to day challenges of life’.
Answer:
Do it yourself.
Something To Do
Question 1.
We can make a continuity tester using the magnetic effect of current. Wrap an electric wire few times around a compass needle box. Make a simple circuit as shown. The free ends of the ‘tester’ can be put in the solution to be tested.
This type of a tester is more sensitive as compass needle shows quite a large deflection even for a weak current. Try repeating some of the activities using this tester.
Answer:
Do it yourself.
Question 2.
Metal polishing substances and their related, wastes and releases, are all potential hazards to human health and the environment, when no managed properly.
Many metal ‘finishing processes’, like electroplating, generate toxic or hazardous pollutants that can result in direct exposure of the employees, and/or pollution of the air, land and water. For example, chromium provides excellent corrosion resistant properties but may lead to liver, kidney, brain and muscle damage. Hence, in the electroplating factories, the disposal of the used conducting solutions is a major concern. There are specific disposal guidelines and methods to protect the environment.
Find out the health concerns, associated with the ‘waste’, in electroplating industries. How are people trying to resolve them?
Answer:
Do it yourself.
Question 3.
Take out the carbon rods carefully from two discarded (discharged) cells. Use them as two electrodes to test the conduction of electricity through various liquids.
Answer:
Do it yourself.
Question 4.
Some of us might have a ‘generator’ fitted in our bicycle. See how the cycle bulb lights up more brightly when the cycle is ‘pedalled’ at a faster rate.
Answer:
Do it yourself.
Question 5.
Solve the ‘crossword puzzle’ with the help of the given clues.
| Across → | Down ↓ |
| 1. Coating a thin film on another material using electricity. | 1. A chemical effect of electric current. |
| 2. The name given to the negative electrode. | 2. ‘Atoms’ that have an electric charge. |
| 3. A conducting liquid. | 3. An expensive metal, often coated on ornaments. |
| 4. The name given to the positive electrode. | 4. A rod, through which an electric current enters or leaves a circuit, having a ‘liquid solution’ as one of its parts. |
Answer:
DAV Class 8 Science Chapter 16 Solutions – Electric Current and Its Chemical Effects Important Questions and Answers
I. Fill in the blanks:
1. Sodium chloride solution is a ________ electrolyte.
Answer:
Strong
2. Vinegar is a ________ electrolyte.
Answer:
Weak
3. Liquids conduct electricity because of movement of ________ .
Answer:
Ions
4. A dry cell converts ________ energy into electrical energy.
Answer:
Chemical
5. A tester made of ________ can detect even very weak current.
Answer:
Magnetic compass
6. Electromagnetic induction was first demonstrated by ________ .
Answer:
Michael Faraday
II. Answer the following questions:
Question 1.
Explain the cause of conductivity of liquids.
Answer:
Movement of ions results in conduction of electricity through a liquid. Molecules of salts, acids and bases break up into free ions; when dissolved in water. These free ions allow the passage of electric current through the solution.
Question 2.
What do you understand by a strong electrolyte?
Answer:
An electrolyte which completely ionizes in a solution is called a strong electrolyte. In case of a strong electrolyte’s solution, a large number of ions are available to conduct electricity.
Question 3.
What do you understand by a weak electrolyte?
Answer:
An electrolyte which partially ionizes in a solution is called a weak electrolyte. In case of a weak electrolyte’s solution, a small number of ions are available to conduct electricity.
Question 4.
Explain the structure of a voltaic cell.
Answer:
An electrolytic solution is kept in a container. Two electrodes are dipped in the solution. The electrodes are connected to electric wires and a resistance or an electrical appliance; like a bulb. Car battery is composed of many voltaic cells. A cell in such a battery is usually filled with dilute sulphuric acid. A zinc rod and a copper rod are used as electrodes in it.
Question 5.
What happens when a steady current is passed through water?
Answer:
When a steady current is passed through water, water decomposes into oxygen and hydrogen. The oxygen bubbles are formed on anode and the hydrogen bubbles are formed at the cathode.
Question 6.
Why do we coat an iron article with chrome?
Answer:
Iron articles are often electroplated with chrome to provide a protective coating. The protective coating prevents the rusting of iron. Rims and handles of bicycle are electroplated with chrome. Bathroom fittings are electroplated with chrome.
IV. Projects:
Question 1.
Make a list of 10 iron articles in your house which are coated with chrome.
Answer:
Do it yourself
Question 2.
Make a working model of a photovoltaic cell and display it in your classroom.
Answer:
Do it yourself