KCL is a ionic compound but HCL is a covalent compound yet both conduct electricity in aqueous solution
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Answer:
The requirement for conduction in solutions is that there must be positively charged ions (cations) and negatively charged ions (anions) in the solution. The cations are attracted by the negative electrode and moves towards it, while anions are attracted by the positive electrode and moves in that direction. This is the mechanism of electrolytic conduction.
As for salts like KCl, they exist as ions even in the solid state (K+ and Cl-). In the solid state, the oppositely charged ions attract each other very strongly and remain near each other. But when placed in water, the water (which is an insulator with a high dielectric constant) enters between the ions and weakens the attraction between them. Therefore the ions separate very easily and can “swim” towards the oppositely charged electrodes and thus conduct electricity.
In the case of strongly polar covalent compounds like HCl or other acids, they are just polar and not separated completely in the pure state. But when dissolved in water, first the water molecules, which are also polar, pulls away the negative and positive ends, thus separating them. This is like one magnet pulling strongly on another magnet where opposite poles attract strongly. Once separated, the H+ and Cl- are covered by insulating water molecules, thus preventing recombination and keeping them separate. These can then conduct electricity.
We can say that salts like KCl dissociate in water easily, while polar covalent compounds like HCl dissociate with some difficulty. But once ionised, they conduct electricity just like salts, because previous history does not matter.
But solutions of all polar covalent compounds do not conduct electricity. For example: alcohols, ethers and aldehydes are polar covalent compounds. But their solutions do not conduct electricity. This is because although weakly polar, they do not separate into ions in water. Water is not strong enough to break the bonds which have more covalent character. But they go into solution because of hydrogen bonding with water molecules. There are no separated ions to move in opposite directions, so no conduction.
Sugar is polar covalent, but sugar solutions do not conduct electricity.
The degree of polarity counts.
Explanation: