Chemical Effects Of Electric Current

Chemical effect:

We can show that electric current produces chemical effect by testing with potato.

When we insert the copper wires of tester in a potato cut half, after sometime we will observe a greenish spot around the wire connected to positive terminal of battery.

This is because current has caused a chemical reaction in the potato

Heating effect:

we can show that electric current produces heating effect by connecting the ends of our tester with an electric bulb.

Due to heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing.

Magnetic effect:

When a compass needle is kept nearby a wire carrying electric current the needle in the compass undergoes deflection even if the current is weak. This deflection is produced due to magnetic effect of current.

it is found that bulb in circuit in setup A glows more brightly than the bulb in circuit in setup B. This happens because there is more heating in the filament in setup A than B.

more heating occurs due to high current flowing through A. Hence solution A is better conductor than solution B.

Disposal of wastes generated from electroplating factory can

(i) release harmful chemicals and toxic compounds into river and is dangerous to the organisms in the river and also pollutes pure water.

(ii) Destroy the quality of crop if released in the cornfield due to toxic chemicals which affect the fertility of the soil.

Therefore, disposal should be done according to disposal guidelines to local authority.

when electric current is passed through a conducting solution, chemical reaction occurs in the solution due to which the solution changes its color.

Also heating, magnetic and lightning effect of current cannot produce color change in solution

Lemon juice contain citrate ions which conduct electricity easily.

Vinegar when dissolved in water break into acetate ions which conduct electricity

Tap water solution is a good conductor of electricity due to presence of dissolved salts in it.

Vegetable oil does not conduct electricity easily because it does not make ions easily.

Chromium has shiny appearance. It does not corrode and resists scratches. That’s why chromium plating is done on many objects such as car parts, bath taps, bicycle rims etc.

On the other hand, iron, aluminium and copper does not have desired characteristics of the extent better than chromium required for electroplating

When sodium chloride is dissolved in water it breaks into sodium and chloride ions which easily conducts electricity.

Similarly, copper sulphate and silver nitrate are solutions of acid and breaks into copper and sulphate ions and easily conducts electricity.

But sugar solution when dissolved in dilute water does not break into ions and hence does not conduct electricity.

(a)

Cathode or negative electrode

In the process of electroplating positive ions are released from the positive electrode or anode into the solution. Now they get attracted by the negative electrode or cathode and get drawn towards it. Therefore, the object to be electroplated is taken as cathode.

Example:

Deposition of copper coating from copper sulphate solution over the copper plate.

This can also be verified by connecting a carbon rod instead of copper at the cathode. on performing electroplating, we get copper coating on the carbon rod.

(b)

Electroplating

Electroplating is the most common use of chemical effect of current.

It is the process of depositing a layer of any desired metal on another material by means of electricity.

(c)

Good conductor

When salt is dissolved in distilled water, we obtain a salt solution which is a good conductor of electricity

(d)

Chromium

Chromium is used for electroplating of such objects because:

1. Applying chromium coating on the metal gives shiny appearance to the object.

2. Chromium coating on the object prevents it from rusting and act as a protective shield.

3. Chromium increase hardness of surface of object.

Zinc is coated over iron to prevent iron from corrosion. The coating of zinc stops oxygen and water to reach the layer of iron metal.

Also, since zinc is more reactive than iron, therefore it reacts with surroundings and hence prevents iron from depletion.

No, the solution of sugar in distilled water will not conduct electricity because sugar dissolves completely in water and no formation of ions takes place. Sugar is neither acidic or basic solution and hence a poor conductor of electricity.

When electric current is passed in an electric circuit, the filament of the bulb starts to heat and then glows due to this heating effect. Hence, the heating effect of current is responsible for glow of bulb in the circuit.

Initially the bulb was not glowing because one cell was not able to provide sufficient voltage to cause the current to glow the bulb.

When one more cell is added in the circuit the voltage across the circuit doubles and it becomes sufficient to increase the current. This current heat the filament of bulb sufficiently and bulb glows.

When experiment is performed using liquid A the bulb glows because A is a good conductor of electricity.

But when liquid A is replaced by liquid B, bulb does not glow because the current is not sufficient to heat the filament. This is because liquid B is a poor conductor of electricity.

In the place of electric bulb, LED can always be used because LED glows even when a weak current flows through it.

For the purpose of depositing silver on iron spoon electroplating must be used. Since the material to be electroplated is iron spoon, it should be connected to the negative terminal of the battery.

Since silver is to be deposited the electrode connected to the positive terminal should be made of silver.

Silver nitrate is used as solution. When electric current is passed silver nitrate breaks into silver and nitrate ions and the silver ions get attracted to the negative plate and gets deposited on the iron rod.

Food cannot be stored in iron cans without any coating because iron is more prone to corrosion due to environment and hence food stored in iron cans will become non-consumable. Therefore, tin is used as a coating over iron as it prevents iron from rusting and also gives a shiny appearance to the can.

Circuit A shows the correct observation because the greenish blue spot is always formed around the positive terminal of battery.

The greenish blue spot is formed due to chemical reaction occurring inside potato. This test could be used to identify the positive terminal of any battery

NO because coal is a poor conductor of electricity. It is instead an insulator……….

……YES, because iron is a good conductor of electricity. Iron is a metal and all metals are excellent conductor …………….

NO, because eraser is made up of rubber which is used as insulator ………………

YES, because steel is a good conductor of electricity…………………….

When an electric current is passed through a conducting solution the following observations may be seen:

1. change in color:

when electric current is passed through a conducting solution, chemical effect of current is seen which can change the chemical composition of the solution. Therefore, depending on the nature of the solution, different chemical changes will take place which may result in change of color of solution.

2. increase in temperature

we know that electric current produces heating effect. when it is passed through a conducting solution, it is possible that solution becomes warmer due to increase in its temperature. This property has many industrial uses.

3.formation of bubbles near the electrode

due to chemical effect of current bubbles can be seen near the electrode. For example, if electrodes are immersed in water and a current is passed bubbles of oxygen and hydrogen are produced. Oxygen bubbles are formed on the electrode connected to positive terminal of battery and hydrogen on the other side

When Boojho performed the experiment of electroplating using two copper plates, copper ions from the positive plate get released into the copper sulphate solution. This copper ions then get attracted to the negative plate or cathode and gets deposited on the copper rod.

When Paheli performed the same experiment using a copper plate and a carbon rod, still carbon rod act as a negative plate or cathode and positive copper ions released in the solution will still get attracted to the carbon rod and will be deposited on them.

Yes, copper will still be deposited on the carbon rod.

We take a pure copper plate and connect it to the negative terminal of the battery. Therefore, plate A is pure copper plate and is used as cathode.

Now, we take another copper plate which is impure and need to be made pure and is connected to positive terminal of the battery. Therefore, plate B is impure copper plate and is used as anode.

Process:

In the process of electroplating, the copper sulphate solution is used. The copper from impure plate is transferred to pure plate and the impurities get settled below the anode. In this way the impure copper plate becomes purified.

When the free ends of the wire do not touch each other there is an air gap between them. Since current does not flow through the circuit in this condition means that air is a poor conductor of electricity.

But it is not that air never conducts electricity. During heavy rainfall and storm, air becomes a good conductor of electricity and during lightning, a current passes through air. During storm, moisture content in air increases and high voltage difference exists.

Yes, the difference is that no current will pass through the circuit when lemon juice is not added to distilled water

Lemon juice contains citric acid which when dissolved in water dissociates into positive and negative ions and the solution starts conducting electricity.

On the other hand, distilled water has absence of minerals and salts and therefore current does not pass through it.

(i)The defection in the magnetic compass indicates that current is flowing through the circuit. The compass needle deflects due to magnetic effect produced by the current.

(ii) the bulb did not glow in circuit A because the current passing through circuit is weak. if the current through the circuit is weak, the filament of the bulb does not get heated sufficiently and it does not glow. This indicates the solution is weak conductor of electricity.

(iii) when we increase the number of turns in the coil wound around the magnetic compass, the magnetic field produced due to current through the circuit increases and deflection in the needle in the compass increases.

(iv) increase in number of cells would increase the voltage across the circuit and would increase the current flowing through circuit. This will result in more increase in deflection of needle in magnetic compass.

1. take out the tray from the match box

2. place a small magnetic compass inside the tray.

3. Take an electric wire and wound it around the tray many times.

4. Now connect the one free end of the wire to one terminal of battery

5. Now take another wire and connect its one end to other terminal of the battery and leave the other end free.

Testing:

For testing any solution, dip the two free ends of wire in the given solution. If the solution is a good conductor of electricity, there is a deflection in the magnetic needle of the compass otherwise no deflection and the given solution is a poor conductor of electricity.