Chemistry [3 Mark Question Answer]

(i) This reaction will take place at the anode of electrolytic cell. This reaction is an example of oxidation of copper atom to copper ion.
(ii) The copper ions will discharge first
Cu²⁺+ 2e^- → Cu
(iii) Carbon tetrachloride is a covalent compound and has no free cations and anions which are responsible for the conduction of electric current.

Electrolytic cell A has completely ionised sodium chloride solution. Thus, the ions can easily migrate to oppositely charged poles and hence the bulb glows brightly. To conclude sodium chloride solution is a strong electrolyte. Electrolytic cell B has a weak electrolyte as only 5% of the acetic acid molecules ionise. Thus, a weak current flows through it and hence the bulb glows dimly.
Electrolytic cell C has a non-electrolytic. Sugar molecules do not ionise and hence no current flows through it. Thus, the bulb does not glow.

(i) Silver ions must be present in electrolyte.
(ii) The anode should be made from silver.
(iii) The article to be electroplated should be made the cathode.

(i) It is because the ions of NaCl can migrate towards opposite electrodes only, they are free to move, i.e., they are either in fused state or solution form.
(ii) It is because silver nitrate has a tendency to hydrolise, but not the silver argentocyanide. Furthermore silver nitrate solution is corrosive to metals like copper used for electroplating.
(iii) In an electrolyte the conduction of electricity takes place due to migration of cations and anions. As no cations or no anions are present in copper therefore it is not an electrolyte. Moreover, a chemical change takes place in an electrolyte during passage of current, but no such chemical change takes place in copper.

(i) The anode is made from impure copper.
(ii) The cathode is made from pure copper.
(iii) Electrolyte is saturated copper sulphate solution, acidified with dil. H₂SO₄.

(i) Carbon tetrachloride is a covalent compound and hence does not have free ions which are responsible for the conduction of current through a liquid.
(ii) Bromide ions discharge at anode to form bromine gas. This gas is highly corrosive and reacts with metallic anode. To avoid corrosion of anode, graphite is preferred as it does not react with bromine and is a good conductor of electricity.
(iii) The acetic acid molecules dissociate very little (about 4%) compared to sulphuric acid molecules (about 90%). Thus, electrical conductivity of dilute acetic acid is less than dilute sulphuric acid.

Complete the table given below :

Electrolyte	Cathode	Anode	Product at cathode	Product at anode
Dil. sulphuric acid	Platinum	Platinum	Hydrogen gas	Oxygen gas
Cu (II) SO4 solution	Copper	Copper	Copper deposits	Copper dissolves
Cu (II) SO4 solution	Platinum	Platinum	Copper deposits	Oxygen gas

(i) Cu - 2e^- → Cu²⁺.
The copper atoms at the anode ionise to form Cu²⁺ ions and enter in the copper sulphate solution.
(ii) 40H^- - 4e^- → 2H₂O + O₂
Hydroxyl ions discharge in preference to sulphate ions.
(iii) O^2- - 2e^- → O
The oxide ions discharge to form oxygen atoms which react with the carbon anode to form carbon dioxide.
C + 2O → CO₂

(a) (1) Cu²⁺ (2) Zn²⁺ (3) Al³⁺ (4) Na⁺.
(b) OH^- will discharge first as its position is lowest in the electronegativity series.

(a) The electrolytes which are very good conductors of electricity and consist of mostly ions in the fused state or in aqueous state are called strong electrolytes.
Examples : (i) Fused lead bromide (ii) Dilute sulphuric acid
(iii) Aqueous sodium hydroxide (iv) Fused alumina in cryolite.
(b) The electrolytes which are poor conductors of electricity and consist of ions as well as molecules are called weak electrolytes.
Examples : (i) Tap water (ii) Aqueous acetic acid solution (iii) Carbonic acid (iv) Ammonium hydroxide solution.