(a)(1) Define each of the following terms: I. deliquescence; II. efflorescence. (ii) Give one example I substance that undergoes each of the processes in (a)(i).
(b) Outline how three colourless gases suspected to be ethane, ethene and ethyne could be distinguished in the laboratory.
(c)(i) What is water crystallization? (ii) Hydrated calcium chloride (CaCl\(_2\) = 111, xH\(_2\)O) contains 49.32% water of cystallization. Calm the value of x. [ (CaCl\(_2\) = 111, H\(_2\)O = 18 ]
(d) Name one calcium compound used (i) in the manufactur cement; (ii) as a dessicant; (iii) in the production of plaster of Paris (POP); (iv) to neutralise acidic soils
(e) A concentrated solution of sodium chloride was electrolysed using graphite electrodes. (i) State the ions present in the solution (ii) Name the products at the I. anode, II. cathode. (iii) Give the by-product of the electrolysis.
Explanation
(a) (i) I. Deliquescence is a process by which a compound absorbs moisture/water from the atmosphere and dissolves in it to form a solution. II. Efflorescence is a process whereby a hydrated salt loses all or part of its water of crystallization when exposed to the air. (ii) Deliquescence: NaOH/FeCl\(_3\)/CaCl\(_3\)/CaCl\(_2\)/POl\(_5\) etc. Efflorescence: Na\(_2\)CO\(_3\).10H\(_2\)O/Na\(_2\)SO\(_4\).10H\(_2\)O/MgSO\(_4\).7H\(_2\)O etc. (b) — To a sample of each of the gases, add acidified KMnO\(_4\)/Br, water (vapour). — No visible reaction shows ethane OR decolourization of KMnO\(_4\)/Br\(_2\) water (vapour) shows ethene and ethyne. —To each of the two remaining samples, add ammoniacal copper (I) chloride/ammoniacal AgNO\(_3\)/Ag\(_2\)O — No visible reaction shows ethene/formation of reddish-brown precipitate/white precipitate indicate the presence of ethyne.
(c) (i) Water of crystallization is the definite amount of water some substances chemically combine with when they form salt from their aqueous solution. (ii) % of anhydrous CaCl\(_2\) is 100 — 49.32 = 50.68%. Number of moles of CaCl\(_2\) H\(_2\)O \(\frac{50.68}{111}\) \(\frac{49.32}{18}\)
