Question

(a) What kind of particles will be found in a liquid compound which is a non-electrolyte? (b) If HX is a weak acid, what particles will be present in its dilute solution apart from those of water? (c) Cations are formed by __________ (loss/gain) of electrons and anions are formed by ________ (loss/gain) of electrons. (Choose the correct words to fill in the blanks.) (d) What ions must be present in a solution used for electroplating a particular metal? (e) Explain, how electrolysis is an example of redox reaction.

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Solution

(a) Molecules are the only particles found in a liquid compound which is a non-electrolyte. (b) If HX is a weak acid, apart from water, its dilute solution contains particles free ions (${\mathrm{H}}^{+}$ and ${\mathrm{X}}^{-}$ ions) and undissociated HX molecules. (c) Cations are formed by loss of electrons and anions are formed by gain of electrons. (d) The ions of the metal that is going to be electroplated on another metal must be present in the solution used for electroplating a particular metal. For example, if a copper wire is to be electroplated with silver, silver ions should be present in the electrolyte. (e) Electrolysis is considered as an example of redox reaction as it involves oxidation and reduction reactions at the electrodes. At cathode, cations are reduced as they receive electrons from the electrode. At anode, anions get oxidised by donating electrons to the electrode. The number of electrons received by anode and the number of electrons donated by the cathode are equal. Let us see an example of reactions at anode and cathode in the electrolysis of molten lead bromide- Reaction at cathode: Lead ions get two electrons from cathode and reduce to lead metal at cathode: ${\mathrm{Pb}}^{2+}+2{\mathrm{e}}^{-}\stackrel{\mathrm{reduction}}{\to }\mathrm{Pb}\left(\mathrm{lead}\mathrm{metal}\right)$ Reaction at anode: Two bromide ions lose two electrons to anode and oxidise to bromine atoms, which combine together to form bromine molecule at anode: $2{\mathrm{Br}}^{-}\stackrel{\mathrm{Oxidation}}{\to }{\mathrm{Br}}_{2}\left(\mathrm{bromine}\mathrm{molecule}\right)+2{\mathrm{e}}^{-}$

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