• CBSE - NCERT - Chemical Effects Of Electric Current (Questions, MCQs)

     

    What is electric current? How does it flow?

     

    Flow of electric charge through a conductor is called electric current.

     

    There are electrons in the atom in various shells around the nucleus.  These electrons carry negative charge. The outermost electrons require the least amount of force to be freed from an atom. 

     

    The flow of electrons from the negative terminal of a source example battery to the positive terminal in a closed circuit is called electric current.

     

    Conventionally flow of electric current is considered from positive terminal to the negative terminal in a closed circuit.  This current is also called Conventional current.


     

    Describe the structure of an atom.

    • An atom is the smallest unit of matter.

    • Nucleus is present at the center of the atom.

    • The nucleus has protons and neutrons.  positively charged particles are called proton neutral particles are called neutrons.

    • The nucleus surrounded by negatively Charged particle orbiting around nucleus called electrons

    • Number of electrons =  number of protons. Hence the atom is electrically neutral.

    • Its electrons in the outermost shell of the atom can move from one atom to another and hands set up electric current.


    Show the direction of electrons and conventional electric current in a circuit.

    Flow of electrons:  negative terminal to the positive terminal of source

    conventional current:  positive terminal to the negative terminal

     


    Electrons closer to the nucleus are hard to remove compared to the electrons far from the nucleus. Why?

     

    Electrons in the outermost shells are free electrons and require less energy to be ejected from the atom. 

     

     The electrons close to the nucleus are attracted more to the positive charge of the protons inside the nucleus, hence need a lot of energy to remove.


     

    What are conductors of electricity? Give an example.

    Substances that allow electric current to pass through them are called conductors example all metals- iron copper silver etc and nonmetals like graphite.

     

    Fllowing electrons contribute to electric current in metal Where are free electrons in the outermost shell which can be ejected from the atom with relatively less energy.


     

    What are insulators? Give some examples.

    Substances which do not allow electricity to pass through them example rubber, dry wood, cotton,  asbestos, plastic, wool etc.


     

    Why are handles of kettles, pressure cookers, electric iron and toasters made of bakelite or wood but not metals?

     

    Plastic,  Bakelite and wood  are poor conductors of electricity and do not allow electric current and heat produced by electricity to pass through them.


     

    Why are electric wires made of copper?

    • Good conductor of electricity

    •  metal that has three electrons in the outermost shell  that can be freed with very less energy


     

    Make an electric circuit to check whether a given substance is conductor or insulator.

     

    Materials: 

    • 5 volt battery

    • switch

    •  insulated copper wire

    •  Bulb

    •  Holder

    •  small pieces of copper,  iron,  glass,  plastic,  wood

    Procedure:

    Conclusion: Bulb glows when the sample material is copper or iron but does not glow when we use plastic glass or wood.


     

    What is meant by the electrical conductivity of a material.  give some examples of substances which have good electrical conductivity And some which do not have.

     

    The ability of a material to conduct electricity or the ability to allow the flow of electric charges is called electrical conductivity.

     

    Examples of good conductors:  iron,  copper,  silver,  aluminium

     

    Examples of bad conductors or insulators:  rubber,  dry wood,  asbestos,  plastic, wool, cotton


     

    How does electrical conductivity depend on the position of electrons with respect to each other?

    If the electrons are loosely bound to the atom e.g.  in case of metals electrical conductivity is high,  in case of nonmetals, electrons are tightly bound to the atom.


     

    Can only solid have good electrical conductivity?

     

    No, Liquids and gases too can be good conductors of electricity.  for example tap water,  salt solution,  milk,  lemon juice.  Distilled water,  sugar solution,  oil,  honey are non electrolyte.


     

    What is an electrolyte? Give an example.

     

    A Liquid that is a good conductor of electricity is called electrolyte. e.g.  Copper sulphate,  sodium chloride,  tap water,  salt solution,  milk,  lemon juice.


     

    With the help of an activity show how different liquids conduct Electricity.

     

    Materials: 

    • 4 beakers

    • 100 ml distilled water

    •  Salt solution

    • Lemon juice

    • Milk

    • A pair of carbon electrodes

    • LED wore

    • Switch

    • 6V or 9V Battery

     

    PROCEDURE:

    • Make a closed circuit using the wire,  LED,  switch and battery and  the two electrodes.

    •  Dip the electrodes in the beaker containing the distilled water. Note down your observation

    •  did the electrode in salt solution,  lemon juice and then milk one by one.  no down your observation

     

    Conclusion: 

    • Bulb glows in case of salt solution,  lemon juice and then milk but does not glow in case of  Distilled Water.

    • Water is a non electrolyte

    •  lemon is a good conductor sense LED bulb glows when electrodes are the Dem lemon juice

    • Salt solution and milk also make the bulb glow.


     

    Why should we choose LED instead of a bulb?

     

    The current conducted by liquid is v and LED can glow even in the presence of weak current whereas a bulb may not


    Why are some liquid electrolytes able to conduct electricity?

    • Liquid contains positive and negatively charged ions

    •  when these ions low electric current is setup

    •  when electricity is passed through tap water It Breaks down to give  hydrogen and Oxygen gas

    •  solutions of acids, bases and salt in water can also conduct electricity Because of presence of large number of free ions

    •  beat electrolyte have negligible or very less number of free charged ions, so they are weak conductors of electricity


    Is pure water a good conductor of electricity?

     

    No, Pure water has no Free charged ions


     

    Why is it dangerous to touch electrical appliances with wet hands?

    Tap water and potable water are not pure and contain several impurities which increase the number of freely charged and in the water making it good conductor of electricity.


     

    Is it advisory for the electrician to carry out electrical repairs during heavy downpour?

     

    During heavy downpour, the pure water gets mixed with suspended particles in the atmosphere, for example Sulphur dioxide, Nitrogen dioxide, Lead and many impurities. These impurities increase the number of freely charged ions in water leading to increase in electrical conductivity.  Hence, electricians may get electric shocks.


     

    Define the terms electrodes anode and cathode.

     

    ELECTRODES: Solid conductor through which electric current enters or leaves and electrolytic cell

     

    ANODE:  The electrode through which the current enters the electrolyte is called anode. it is positively charged.

     

    CATHODE: The electrode through which the current leaves the electrolyte is called cathode. it is negatively charged.


     

    What is an electrolytic cell?

     

    A device containing two electrodes in contact with an electrolyte that brings about a chemical reaction when connected to a battery is called an electrolytic cell.


     

    What is meant by the term electrolysis?

    When electric current is passed through an electrolyte ( good conductor of electricity),  it initiates a chemical reaction that split up the chemical compound present in electrolyte into its constituent substances.  Thus,  the chemical effect of current and the chemical changes are seen in the electrolyte. This process is called electrolysis.

     

    Example: When electric current is passed through water,  its splits into hydrogen and oxygen.


    Describe electrolysis of water. Name the gas(es) liberated at the electrodes during electrolysis of water.

     

    • When electric current is passed through water containing small amount of sulphuric acid,  water split into hydrogen and oxygen.  The bubbles of hydrogen are formed at the cathode ( negative electrode)  while bubbles of oxygen are formed at the anode ( positive electrode).

    • H2SO4 is added to increase the conductivity of water

    • Industries use this method to generate hydrogen and oxygen gases

    • Twice as much hydrogen is produced as oxygen



     


     

    Which substances are formed at the electrodes when electrolysis of copper chloride is carried out?

    • Copper chloride (CuCl2) gets split into Copper and chlorine.

    • CU is collected at negative electrode that is cathode

    • Cl is collected at positive electrode that is anode

    • Twice as much Cl is collected as Cu


     

    Why does the blue colour of copper chloride Fade away gradually during electrolysis?

    • CuCl2 dissociates into Copper and chlorine during electrolysis. 

    • Copper Gets collected at cathode

    • Chlorine get selected at anode 


     

    What is meant by electroplating? Why is it done?

    • Electroplating is the process of coating a metal or an alloy with another metal using the process of electrolysis. 

    • It is done to protect various metals from corrosion

    • In hands a visual appearance of objects


     

    Explain the process of electroplating copper on an iron nail.

    • Take copper sulphate in a beaker as an electrolyte.

    •  connect an iron nail to the negative terminal of the battery

    •  connect the copper plate to the positive terminal of the battery if the help of wire and a key between them

    •  Dip them in the solution of copper sulphate 

    •  press the key

    •  copper collecting on Iron nail because The positive ions of copper move towards the cathode (negative electrode)

     

    Here the material to be coated with a layer is used as anode

    The material of which the coating is to be obtained is used as cathode

    Solution of the same material of which coating is to be obtained is used as an electrolyte


     

    What are the applications of electroplating?

    (a) Jewellery for lustre

    (b) zinc is electroplated on Iron to prevent corrosion

    (c) Thin layer of chromium is used on car parts for smooth texture and aesthetic looks

    (d) Reducing friction by elctroplating and making the surface smooth

    (e) Protection from radiation by using suitable materials


     

    A copper vessel needs to be electroplated with silver. Name the anode and the electrolytes you will use for this purpose.  Draw a labeled sketch of this experiment.

     

    ANODE: Desired material to  be coated,  ( silver )

    CATHODE: Material on which coating needs to be done

    ELECTROLYTE: salt solution of the anode (silver nitrate) 

     

    Make a circuit with a copper vessel connected to the negative terminal of the battery with the help of a piece of wire. 

    Connect the silver medal to the positive terminal of the battery with the help of wires and the key between them.

     Put them in the solution of silver nitrate.

     when electric current is passed through the setup the cations of silver from silver nitrate solution towards the negative terminal and get neutralized by the electrons there. As a result neutral atoms of silver get deposited on copper vessel.

     

    The electrons present at copper vessel or the cathode at transferred from silver metal present at the anode.  this make the cations of metal deposit at the anode. 


     

    Name the three effects of electric current.

    1. Heating

    2. Magnetic

    3. Chemical


     

    In charging a battery of a motor car,  which effect of electric current is used and why?

    Chemical Effect of Electric CurrentBecause the electrons flow from the battery to the motor car in the form of chemical energy.  the flow from higher potential of battery to lower potential of motor car.


     


    Chemical effect of electric current may cause

    1.  formation of gas Bubbles at the electrodes

    2.  deposition of metal on the electrodes

    3.  change in colour of the solution

    4.  all of the above


     

    Electroplating does not help in which of the following cases?

    1.  fine finish

    2.  Luster

    3.  hardening of metal

    4.  prevention from corrosion


     

     Upon dissolving in water, ____________  starts conducting electricity

    1. NaCl

    2. Sugar

    3. Oxygen

    4. Kerosene 


     

    ____________ Plating is done on objects such as car parts,  bath taps,  kitchen gas burners,  bicycle handlebars,  wheel rims  because of its shining appearance.

    1.  Nickel

    2.  Chromium

    3.  Carbon

    4.  Iron


     

    A coating of____________  is done to iron to prevent it from corrosion.


     

    Electrode that is joined with the negative terminal of the battery is called ____________.

     

    Electrode that is joined with the positive terminal of the battery is called ____________.

     


     

    A tester is used to check the conduction of electricity to two liquids labeled A and B.  it is found that the bulb of the tester glows brighter for liquid A and trader for liquid B.  This is primarily because

    1.  liquid A is better conductor of electric current

    2. Amount of electrons flowing in liquid are more

    3. both the above

    4. none of the other


     

    Which of the following metal can be used for electroplating

    1. Copper

    2.  Silver

    3.  Chromium

    4.  All of the above


     

    For electroplating the material to be electroplated is made the ____________  end the metal which is to be plated is made the ___________.

     

    1. Cathode, Anode

    2. Anode, Cathode

    3. Anode, Anode

    4. Cathode, Cathode


     

    Food Containers used for storing food are made by electroplating

    1.  tin onto iron

    2.  chromium onto iron

    3.  iron onto tin

    4.  iron onto chromium 


     

    When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

     

    The deflection occurs because the circuit becomes complete when free ends of the tester are dipped in a solution. The solution is certainly a conducting solution. This is the reason why the compass needle shows a deflection.


     

    Name sea household liquids that you can use to  exhibit electrolysis

    1.  lemon juice

    2.  saltwater

    3.  vegetable oil

    4. All of the above



     

     
    Additional Content

    Applications of Electrolysis and Electroplating

     
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Material : CBSE - Class 8

Topic : NCERT - Chemistry

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