DAV Class 8 Science Solution Chapter 16 Electric Current and Its Chemical Effects
DAV School Books Class 8 Science Solution Chapter 16 Electric Current and Its Chemical Effects all Question Answer. DAV Class 8 16th Chapter Electric Current and Its Chemical Effects full Chapter explanation by expert teacher.
DAV School Books Class 8 Science Solution Chapter 16 Electric Current and Its Chemical Effects
A.) Fill in the blanks.
1.) Most liquids, that conduct electricity, are solutions of ___________, ___________ and ___________.
2.) The ___________ the concentration of an ion in the solution, the greater is the conductivity of the solution.
3.) The passage of an electric current, through a solution, can cause ___________ effects.
4.) When electric current is passed through copper sulphate solution, copper gets deposited on the plate connected to the ___________ terminal of the battery.
5.) The process, in which electricity is used to deposit a thin layer of any desired metal on another metallic object, is known as ___________.
6.) The faster is the relative motion between the magnet and the (closed) coil, the ___________ is the current that flows through the coil.
Answer: (1) acid, base, salt (2) greater (3) chemical (4) negative (5) electroplating (6) stronger
B.) Write True or False for the following statements.
1.) A solution of silver nitrate is a good electrolyte.
2.) An electrolytic cell consists of a cathode, anode and an electrolyte
3.) Oxygen gets liberated at the anode during the electrolysis of acidified water.
4.) Electrorefining is the process of coating one metal on another using an electric current.
5.) The phenomenon of ‘Electro-magnetic Induction’ was discovered by the Italian Scientist, Alessandro Volta.
Answer: (1) True (2) True (3) True (4) False,Electrorefining is the process of purifying a metal (5) False, it was discovered by Michael Faraday
C.) Tick the correct option.
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-
Answer: B and D
2.) Electrolytes conduct electricity due to the movement of-
Answer: positive as well as negative ions.
3.) The electrode, connected to the positive terminal of a battery, is known as the-
Answer: anode
4.) The phenomenon of decomposition of an electrolyte, when electricity is passed through it, is known as-
Answer: electrolysis
5.) The process, of coating of (say) iron with chromium, is known as-
Answer: electroplating
D.) Answer the following questions in brief.
1.) State the appropriate term, used for a liquid or solution, which can conduct electricity (along with some accompanying chemical changes).
Answer: Electrolyte
2.) Distinguish between strong and weak electrolytes. Give two examples of each.
Answer: Strong electrolytes are substances that, when dissolved in water, totally disintegrate into ions. Examples include hydrochloric acid and table salt (NaCl) (HCl).
Weak electrolytes are substances that, when dissolved in water, partially breakdown into ions. Examples include carbonic acid and acetic acid (CH3COOH) (H2CO3).
3.) Name the device that converts-
(a) Chemical energy into electrical energy.
Answer: Cell
(b) Mechanical energy into electrical energy.
Answer: Generator
4.) Name the scientists who introduced the (scientific) world to the-
(a) voltaic cell
Answer: Alessandro Volta
(b) phenomenon of electrolysis
Answer: Michael Faraday
(c) phenomenon of electro-magnetic induction
Answer: Michael Faraday and Henry
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.
Answer: Electrodes A -anode
Electrodes B- is cathode.
(b) Name the process associated with the circuit shown here.
Answer: Electrolysis
6.) State the meaning of the terms:
(a) Electro-magnetic induction
Answer: Electromagnetic induction is the process of inducing an electric current in a conductor by exposing it to a changing magnetic field. It is the basis of many electrical technologies, including electric motors, generators, transformers and inductors.
(b) Electrolysis
Answer: Two electrodes that are submerged in the liquid electrolyte are used in the procedure, and when they receive an electric current, the electrolyte’s ions are drawn to them and a layer of material is formed on their surfaces. Once this layer of material has been taken from the electrode’s surface, the procedure can be repeated until the required amount of material has been eliminated. For electroplating or the purification of metals, electrolysis is frequently used to extract metals from a solution.
(c) Electrodes
Answer: A metal that permits an electric current to flow through an electric cell and is utilised in the electrolysis experiment setup.
(d) Electrorefining of metals
Answer: Electrorefining of metals is the technique of electrolyzing contaminated metals to create pure metal.
7.) State three uses of the phenomenon of electrolysis.
Answer: The three uses of the phenomenon of electrolysis are:
- Metal extraction from ores involves the use of electrolysis.
- In the electroplating procedure, a thin layer of metals is deposited on a surface using electrolysis.
- Systems for treating water employ electrolysis to filter out pollutants and minerals.
E.) Answer the following questions.
1.) Give reasons for the following:
(a) Solid chloride does not conduct electricity while sodium chloride solution conducts.
Answer: The solid chloride molecules are linked together by strong covalent bonds that prevent electrons from moving freely and carrying an electric current. When solid chlorine is dissolved in water, the strong covalent connections are broken, allowing the ions to move freely and generate an electric current. As a result, sodium chloride solution conducts electricity while solid chloride does not.
(b) It is not safe to carry out electrical repairs outdoors during a heavy downpour.
Answer: It is dangerous to perform electrical repairs outside during a heavy downpour because there is a risk of electrocution from rainwater coming into direct contact with unprotected electrical wiring. Water and electricity are a dangerous combination that can cause short circuits, shocks, and fire. Additionally, the high humidity and the damp atmosphere increase the likelihood of falling or slipping, which could lead to further injuries. Additionally, due to high gusts during a storm, the risk of electric shocks may rise as exposed unsecured wires. It’s imperative to wait until the storm has passed before carrying out any external electrical repairs.
(c) To carry out electrolysis of water, a few drops of sulphuric acid are (carefully) added to the water.
Answer: An electrolyte solution is made by mixing some water with a few drops of sulfuric acid. Electrolysis cannot take place without this because the electrolytes’ ions act as a conduit for the electric current. The concentrated sulfuric acid’s copious supply of hydrogen ions in the water speeds up the process as well.
(d) Kitchen gas burners are often coated with chromium.
Answer: Since chromium is so exceptionally resistant to corrosion and because kitchen gas burners are subjected to extremely high temperatures as well as the elements, chromium is frequently used to coat the burners. Additionally, because chromium is a fairly strong metal, it is more resistant to wear as well as tear and more durable. Last but not least, chrome is a polished metal that is simpler to clean and preserve.
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 distilled water.
(a) In which Set-up will the bulb glow the brightest? Justify your answers.
Answer: In Set-up as we know that sodium chloride is a strong electrolyte.
(b) In which Set-up will the glow of the bulb be quite dim? Justify your answers.
Answer: In Set-up B since acetic acid happens to be a weak electrolyte.
(c) In which Set-up will the bulb not glow at all? Justify your answers.
Answer: In Set-up C as distilled water is a bad conductor of electricity.
3.) Ramit sets-up the circuit shown below for purification of copper:
(a) Name the metals used for Electrodes A and B.
Answer: Impure copper -electrode A and pure copper -electrode B.
(b) Name the process of purification.
Answer: Electrorefining
(c) Name the solution that needs to be used.
Answer: Copper sulphate
4.) (a) Define ‘electroplating’. How can steel spoons be plated with silver? Explain with the help of a diagram.
Answer:
By running a current of electricity through a solution comprising a dissolved metal, the process of electroplating coats an item with a light coating of metal. By putting steel spoons in a silver plating liquid and running an electric charge through it, steel teaspoons can be coated with silver. The spoon and the solution’s silver atoms interact, forming a tiny film of silver on the top.
(b) State any three uses of electroplating.
Answer: The uses of electroplating involves the following:
- Metals and alloys can be electroplated to increase their corrosion resistance.
- Additionally, it is applied to make equipment and instruments more resilient.
- It is applied to improve the electrical properties of parts like switches and circuit boards.
5.) Describe an experiment to show that we can get electrical energy by using a magnet.
Answer: Making a basic generator is an experiment that demonstrates how we can generate amount of electricity by using a magnet. An apparatus that transforms mechanical energy into electricity is a generator. Get a magnet, a coiled of cable, a Dc power supply, and a multimeter to carry out the experiment. The DC motor’s shaft is first linked to the wire coil. The magnet is then positioned close to the coil but not contacting it. Using a multimeter, the initial voltage between the coil’s terminals is determined. The shaft is then rotated by the DC motor, which causes the coil to move toward the magnet.
A voltage is used to identify the electrical current that is caused by the coil’s rotating magnetic field. The multimeter is used once more to measure the final voltage all across coil’s terminals. The electrical energy that was produced by the magnet is represented by the change in voltage between the original and final values. The amount of electrical energy produced increased with the size of the differential. This experiment shows that moving a magnet close to a coil of wire causes the coil to create an electrical current, producing electrical energy. This is how a generator, which is frequently used to produce energy in power plants, works on a fundamental level.
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?
Answer: Bulb glows.
(b) pulled out of the coil?
Answer: Bulb glows.
(c) held stationery within the coil?
Answer: Bulb does not glow.