The study of coordination compounds is an important aspect of Chemistry Topics, as it examines the bonding and reactivity of metal complexes.
Applications of Chemical Effects of Electric Current
Electric current can bring about chemical changes, so it is said to have a chemical effect. For example, when electric current is passed through acidified water by using carbon electrodes, then a chemical reaction takes place to form hydrogen gas and oxygen gas. This chemical reaction can be written as :
Water is a chemical compound, and hydrogen and oxygen are elements. So, in this reaction, a chemical compound ‘water’ has been decomposed into two elements, hydrogen and oxygen, by the action of electric current. So, this reaction is an example of the chemical effect of electric current. The breaking up of water into hydrogen and oxygen is actually a ‘chemical decomposition reaction caused by passing an electric current through acidified water (which is a conducting liquid).
The chemical decomposition produced by passing an electric current through a conducting liquid is called electrolysis. The decomposition of acidified water into hydrogen and oxygen by passing an electric current (or electricity) is an example of electrolysis. Please note that pure water is not a good conductor of electricity. Water is made an electricity ‘conducting liquid’ by the addition of a small amount of acid to it.
The water containing a little of acid is called ‘acidified water’. We use acidified water for carrying out the electrolysis of water. We can also add some base (such as sodium hydroxide) to make water a good conductor for carrying out its electrolysis. Water can be decomposed into hydrogen and oxygen gases by electrolysis. This can be demonstrated as follows.
To Demonstrate the Chemical Effect of Electric Current
We will now describe an activity to demonstrate the chemical effect of electric current.
Take out two carbon rods from two discarded dry cells carefully. Clean their metal caps with sand paper. Wrap copper wires around the metal caps of the carbon rods and join them to a battery through a switch (see Figure).
We call the two carbon rods ‘carbon electrodes’ or just ‘electrodes Take 250 mL of water in a beaker. Add a few drops of dilute sulphuric acid to water to make it more conducting. Now, immerse the carbon rods (or carbon electrodes) in acidified water in the beaker (see Figure).
Make sure that the metal caps of the carbon rods are above the level of water in the beaker. Pass electric current through acidified water in the beaker by closing the switch. Wait for 4 to 5 minutes and observe the two carbon electrodes carefully. We will see that the bubbles of gases are produced at the two carbon electrodes.
The formation of gas bubbles at the two carbon electrodes shows that a chemical change (or chemical reaction) has taken place in water on passing electric current through it.
In the year 1800, a British chemist, William Nicholson, had shown that if electric current is passed through acidified water, then bubbles of oxygen gas and hydrogen gas are produced at the two electrodes immersed in it.
- Oxygen gas is formed at the positive electrode (anode) which is connected to the positive terminal of the battery, and
- Hydrogen gas is formed at the negative electrode (cathode) which is connected to the negative terminal of the battery.
We have just described the chemical effect of electric current on water (or rather acidified water). An electric current can also produce a chemical effect on some other substances such as acids, bases, salt solutions and certain molten compounds (melted compounds). When an electric current is passed through these liquids (or molten compounds), chemical reactions take place.
We call these chemical reactions electrolysis’. From this discussion we conclude that when an electric current flows through a conducting solution, it causes a chemical reaction (or chemical change). The chemical reactions brought about by an electric current may produce one (or more) of the following effects :
- bubbles of a gas (or gases) may be formed on the electrodes.
- deposits of metals may form on electrodes.
- changes in colour of solutions may occur.
These are some of the chemical effects of the electric current. The chemical effect produced by an electric current depends on the nature of conducting solution (through which it is passed), and on the nature of electrodes used for passing the electric current.
For example, bubbles of gases are formed when an electric current is passed through acidified water ; deposit of metal is formed when electric current is passed through copper sulphate solution (during electroplating); and a change of colour occurs when electric current is passed through a cut potato.
To Demonstrate the Change in Colour Caused by the Chemical Effect of Electric Current
Cut a potato into two halves. Take one piece of cut potato and insert two iron nails into it a little distance apart from one another (see Figure). The iron nails are the two electrodes in this case. Connect the two terminals of a battery to the two iron nails by including a compass and a switch in the circuit as shown in Figure.
Pass the electric current through cut potato piece by closing the switch. We will observe a deflection in the compass needle showing that potato conducts electricity to some extent. Let us continue to pass electric current through potato piece for about half an hour. We will notice a greenish-blue spot on the cut surface of potato around the iron nail which is connected to the positive terminal of the battery (see Figure).
There is, however, no coloured spot around the other nail which is connected to the negative terminal of the battery. The formation of a greenish-blue spot around the positive electrode inserted in the surface of a cut potato shows that the chemical effect of current can bring about change in the colour of a conducting solution (A fresh potato contains solution of many substances dissolved in water). Thus, an electric current produces a chemical effect in potato leading to a change in colour.
The fact that a greenish-blue spot on potato surface is always formed around the electrode connected to the positive terminal of a battery can be used to identify the positive terminal of a battery which is concealed in a box (and whose terminals cannot be seen from outside). From the above activity we conclude that the fresh fruits and vegetables conduct electricity to some extent due to the presence of various salt solutions in them. Some fruits and vegetables also contain acid solutions in them.
Applications of The Chemical Effect of Electric Current
The chemical effect of electric current is used in industries (or factories) for the following purposes:
- Electroplating metals,
- Purification of metals,
- Production of certain metals from the ores,
- Production of chemical compounds, and
- Decomposing chemical compounds.
We will now describe all these applications of the chemical effect of electric current in somewhat detail, one by one. Let us start with electroplating. Please note that in the term ‘electroplating’, the word electro’ stands for ‘electric current’ and ‘plating’ means ‘the act of covering a metal object with a thin layer or coating of a different metal’. Electroplating is one of the most common applications of the chemical effect of electric current.