(a)(i) What is an electrolyte?
(ii) Classify each of the following as strong electrolyte/weak, electrolyte/non-electrolyte. Potassium chloride; sodium ethanoate, aqueous ammonia; cane sugar
(b)(i) Write half-cell equations for the reactions in the Daniel cell .
(ii) Why is the Daniel cell classified as an electrochemical cell?
(iii) Give two other examples of electrochemical cell.
(c) Explain the following observations.
(i) Graphite conducts electricity, unlike most non-metals
(ii) In the electrolysis of copper (II) tetraoxosulphate (VI) solution, the blue colour fades with platinum electrodes while the colour intensity is unaffected with copper electrodes (equations required)
(iii) A solution of dry hydrogen chloride in methylbenzene (toluene) does not conduct electricity whereas hydrochloric acid does.
Explanation
(a)(i) An electrolyte is defined as a compound which when in solution or molten state, conducts an electric current and is decomposed by it.
(ii) Potassium chloride is a strong electrolyte; Sodium ethanoate is a strong electrolyte; Ammonia\(_{(aq)}\) is a weak electrolyte; Cane sugar is a non-electrolyte
(b) Electrochemical Cells.
(i) Reaction in the Daniell cell;
At the Anode: Zn ---> Zn\(^{2+}\) + 2e\(^-\).
At the Cathode: Cu\(^{2+}\) + 2e\(^-\) ---> Cu
(ii) The Daniell cell is classified as an electrochemical cell because it converts chemical energy into electrical energy or current.
(iii) Two other examples of electrochemical cells are Dry cell/Leclanche cell, Lead accumulator/Car battery, Weston/Cadmium cell; Ni/Fe cell (any two)
(c)(i) Graphite conducts electricity because it contains decolourized or mobile electrons which carry the current.
(ii) Electrolysis of CuSO\(_{4(aq)}\) with platinum electrodes. Cu\(^{2+}\) responsible for the blue colour is continuously removed from the solution and deposited at the cathode as copper. The colour fades gradually. Cu\(^2\) + 2e --> Cu. Electrolysis of CuSO\(_4\) with copper electrodes. As Cu\(^{2+}\) is discharged and Cu deposited at the cathode, an equal amount of copper goes into solution (i.e. Cu\(^{2+}\)) or ionizes at the anode. Cu —> Cu\(^{2+}\) + 2e\(^-\). This maintains the colour intensity
(iii) The solution of HCI in methylbenzene does not conduct electricity while hydrochloric acid does, the reason being that hydrogen chloride molecule is covalent in character and its covalent nature is preserved in organic solvent or it does not ionize in organic solvent. Water is required to make it ionize and conduct electricity as in the case of hydrochloric acid.