Science Chapter 14 Chemical Effects Of Electric Current

acids

bases

salts

chemical

negative

electroplating

Solution has ions present in it causing electric current. Electric current produces magnetic effect causing deflection of the magnetic needle of a compass. Therefore, when a tester is dipped in the solution, the needle shows deflection, being a good conductor of electricity. 

Tap water, lime water, vinegar may cause the magnetic needle to deflect as they conduct current because of the presence of ions in it. 

The bulb does not glow and the possible resons for the absence of light are:

1. The bulb may be fused.
2. Connection of the wires may be loose. 
3. Probably the solution may not be a good conductor of electricity. 

A.

liquid A is a better conductor than liquid B.

Some salt can be added to it to make it a conductor. This way water will conduct electricity. Presence of ions makes the water conducting. 

Water being a good conductor of electric current is capable of conducting electricity causing electric shock. Therefore, to save themselves and other people from electrocution the firemen shut off the main electrical supply. 

Drinking water contains less ions in it as compared to the sea water.

Drinking water is processed and purified before supplying it to the houses. Thid way due to the removal of salts and minerals, the conductivity has been reduced. 
Sea water being rich in salts, acidic and basic substances is a better conductor of electricity. Therefore, the compass needle deflects more in seawater. 

 During heavy downpour, outdoor electrical connections should not be repaired. Water being a good conductor of electricity, causes electrocution. 

Raindrops get mixed with the suspended particles of the air during the downpour. Thus, the raindrops no longer remain pure. It becomes a mixture of salts and other impurities thereby, cinducting electricity. 

Electroplated objects around us are:

Rims of cycles, door handles, taps, showers, metallic pens, artificial jewellery, utensils, metallic almirahs, buckles of clothes and belts etc.

The copper rod should be attached to the positive terminal because the free ions will get attracted towards the negative terminal, and gets deposited there. So, copper from impure rod will get collected in the pure copper plate. 

Conductors are the substances which allow the electric current to pass through them. 

Insulators are substances which do not allow electric current to pass through them. 

Copper.

Plastic.

Liquids having ions are good conductors of electricity. 

Liquids that conduct electricity are solutions of acids, bases and salts. 

Tap water is a good conductor. 
Distilled water cannot conduct electricity as it does not conain any impurities or salts. 

Distilled water can be made good conductor by adding some salt, acids and gases. Salts and impurities conduct electricity. 

Tester can be used to check if the liquids conducts electricity. If the tester glows, liquids conduct, or else not.

Two substances other than water which conducts electricity are:

(i) Lemon juice.

(ii) Vinegar.

LED is Light Emitting Diode which glows even for a small or low value of current. 

Light Emitting Diode

Electrodes are the metal rods which are dipped in liquids, to which cells are attached are called electrodes. 

Electrode is a medium of conduction of electricity. 

Examples of chemical effects of current are:

(i) Electrolysis.

(ii) Electroplating.

Electrolysis is the process of decomposition of an electrolyte on passing electricity through it. 

Hydrogen is evolved at the cathode during the electrolysis of water. 

Solution A is better conductor as the intensity of light is more for bulb A. 

Electroplating is the process of coating a layer of desired metal on other metallic surface by means of electricity. 

Electrolysis.

On hydrolysis of slightly acidic water, we get Hydrogen and Oxygen gas.

Chemical effects of Electric Current.

Four liquids which can conduct electricty are Lime water, Lemon juice, Vinegar and Tap water.

Electro-refining is a process in which melats such as gold, silver and copper are refined by means of passing electricity through them. 

Air having impurities present in them is a good conductor.

Chemical effect of Electric current is illustrated. 

Liquids can be tested to check if they are good conductors of electricity. The free ends of a tester is dipped into liquid to be tested for the glowing of bulb. If the bulb glows, then it is good conductor and if the bulb does not glow, it is a poor conductor. All liquids are not good conductors of electricity. 

When electric current passes through a bulb, the filament of the bulb heats up to a high temperature. This is called heating effect of current. The temperature is so high that it starts glowing. 

However, if the current through a circuit is weak, the filament does not get heated up sufficiently and it does not glow. 

When current passing through is very weak, the bulb will not glow because the temperature is low. Magnetic compass is used to detect the presence of current. In the presence of electric current, the compass will show deflection indication the presence of current around the compass. 

LED is Light Emitting Diode. LED consists of a bulb, two legs called leads. One leg is longer than the other. Longer leg is attached to the positive terminal of the battery and shorter leg is attached to the negative terminal of the battery. Even a small amount of current will make the LED glow.

LEDs are as shwon below in the figure: 

When a small amount of current is flowing through the conductor, the bulb will not glow as the filament of the bulb will not get heated up. 
Hence, inorder to detect the presence of small value of current, we need magnetic compass. The magnetic compass will get deflected even if there is a small value of current. 

Objectives of electroplating are:

(i) Electroplating is done for decoration purposes.
For example, silver or gold plating of brassware such as flower vase. 

(ii) Electroplating is done inorder to prevent corrosion. Iron objects can be protected from rusting by electroplating them with nickel. 

Water that we get from sources like tap, hand pumps, wells and ponds have impurities in them. These water contains salts dissolved which will dissosciate to form ions. Hence, they conduct electricity. 

Distilled water is pure and will not contain any impurities. Hence, due to the absence of ions in distilled water, they will not conduct electricity.

The passage of an electric current through a conducting solution causes chemical reactions. The process in which chemical reaction takes place in a solution on passing electricity through it is because of chemical effect of current.

 For example, change in colour of solutions and electroplating.

Air is an insulator when it is not damp. But, once, it is damped, it acts like conductor.

This can be shown by using a tester.

When the free ends of tester do not touch each other, there is an air gap between their ends. As air is a bad conductor, circuit is not complete and hence, the compass does not shows deflection. 

Therefore, air is an insulator. 

Tester is an instrument which is used to check the flow of electric current. It is attached to the either terminals of the electric circuit. If the bulb attached to tester glows, it confirms the passage of current. 

The experiment is illustrated in the figure below: 

Substances which allow the passage of electric current through them are called conductors.

Substance through which current passes partially or in small quantity, they are called bad conductors.

Substances like copper, iron, aluminium etc., are called conductors. 

Substances which do not allow the electric current to pass through them are called insulators. Electric current do not pass through them and do not show any effect of electric current. Substances like wood, plastic, rubber, distilled water etc., are insulators.

(i) EIectrolysis : It is the process of decomposition of a chemical compound in aqueous solutions or in molten state by a chemical change by using direct electric current.

(ii) Electrolyte : It is a compound which either in aqueous solution or in the molten state allows an electric current to pass through it. It decomposes into neutral atoms at the two electrodes.

There are four components of this circuit.

It has a three celled battery, a bulb, conducting wire, and an open switch.

Conducting wire has all the three components attached to it.  

Distilled water has no impurities in it. Due to the absence of ions, distilled water does not allow conduction of electricity. On adding salt or lemon juice to the distilled water, it starts to conduct electricity. Hence, due to the presence of electric charge, the mgnetic compass shows deflection. 

The circuit diagram for the same is shown below. 

Two methods to test conduction are:

1. We use an electric lamp to test conductivity. Here, an electric lamp is attached in the electric circuit. The substance whose conductivity is to be checked is also connected to the circuit. On passing current through the substance, if the lamp glows, then it is a good conductor of electricty. 

But, the lamp will not glow when the current through the substance is weak. To detect the presence of small value of current, magnetic compass is required. 

2. Electric compass is coiled with conductive wire. When current is allowed to pass through it, it creates a magnetic field and the compass shows deflection, showing the presence of current in the circuit.

The circuit diagram for both the methods is shown below:

The experimental set-up for electroplating copper on an iron spoon is shown in Fig.



In the electrical set up, the iron spoon is made cathode (-ve electrode) and a thin sheet of pure copper is made anode (+ve electrode). The electrolytic solution is an acidified solution of copper sulphate.

When electricity is passed through copper sulphate solution, the copper metal gets dissolved in the solution and gets electroplated on the iron spoon.

Electroplating has many advantages: 

(i) It is used to coat metal surfaces with desired metal coatings, for decoration purposes.

(ii) It saves metal surfaces from rusting.

(iii) It saves corrosion of surfaces of metals.

(iv) Coating of chromium on metals give luster to objects. 

(v) Cheap metals like iron, aluminium etc., can be coated with costly metals like silver, gold etc., to give them rich look as in case of artificial jewellery.

(vi) It can make reactive metals like iron etc., less reactive and they can be used for storing food items etc. 

A current carrying wire behaves like a magnet. This can be proved using the following activity.

As in the figure, a wire is fixed along the edge of a table. 

 

Place a magnetic compass near the wire. Connect the two ends of the wire to a battery cell. And, we can see that the magnetic compass will deflect. Hence, the deflection proves that a current carrying wire behaves like a magnet. Now, place the compass at different points on the table at varying distances from the wire. Observe the deflection in each case.

When the current is stopped, the associated magnetic property also vanishes. Therefore, current is required in the wire, for it to behave as a magnet. 

The steps to make an electric pen is mentioned below: 



1. Take a filter paper and soak it into potassiumiodide and starch solution.
2. Spread the filter paper on a metal sheet. 
3. Now join two connecting wires to the terminals of battery. 
4. Attach the wire connected at positive end to the plate.
5. Now, write on the sheet attached to the negative terminal of the battery. On the segments where you are writing, blue color will appear. 

This happen due to electrolysis of potassium iodide solution which produces iodine. Iodine on reaction with starch produce ink of blue colour. 

Electroplating

electrolyte

insulator

circuit

insulator

electric current 

acids

bases

salts

electrolytic cell

Sulphuric acid

ethyl alcohol 

negative

B.

chemical effect of electricity

C.

a liquid that conducts current

C.

electroplating

D.

both (b) and (c)

A.

a good conductor of electricity

C.

Wood

D.

Copper

A.

Distilled water

C.

Chemical effect

B.

coating a metal on another metal using electric current

i) LED is shown in the figure.

Difference between LED and electric bulb:

(b) The full form of LED is Light Emitting Diode.

Sea water contains a large amount of dissolved salts in it. Due the presence of a large amount of dissolved ions, sea water conducts electricity. 

Drinking water contains only a small amount of dissolved salt in it.

The greater electric current passing through sea water produces stronger magnetic field in wire and hence deflects the compass needle more.