ALS10A - Section 10/ The p-Block Elements / Suggested...

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Section 10/ The p-Block Elements / Suggested solutions / SKH Bishop Baker Secondary School AL Chemistry Section 10 The p-Block Elements 81 IIB Q.6 (d) The sample is first treated with an oxidizing agent (say acidified dichromate(VI)).[ ½ ] + [ ½ ] Carbonate still turns limewater milky [ ½ ] but sulphite will not . [ ½ ] 81 IIB Q.8 (b) Material must be resistant to HNO 3 (conc.) or H 2 SO 4 (conc.) e.g. glass, CF 2 - CF 2 polymers or iron(passive). Best to have steel(strength)tank lined with glass or p.t.f.c.(chemically resistant). [2] (c) Clean the area to keep people out of contact with liquid and with fumes. Wash down with large quantities of water, using water carefully to ensure that no splashing occurs or violent exothermic reactions. [2] (d) Uses : 4 uses of conc. HNO 3 or H 2 SO 4 . or good general account of fertilizers (H 2 SO 4 , HNO 3 ) or chemical industry (impression marking) [1 each] EITHER Conc. HNO 3 is used as : (1) a vigorous acid oxidizing agents (e.g. cleaning metal surface etching) (2) as nitrating agent (e.g. manufacturing of nitro-compounds) (3) specific compounds are explosives. (e.g. nitrocellulose glycerine) (4) used as fertilizers. (e.g. ammonium nitrate) OR Conc. H 2 SO 4 is used as : (i) chemical reactants (ii) fertilizers, e.g. ammonium sulphate. (iii) industries (with phosphate rock to give superphosphate or phosphoric acid) (iv) a mineral acid (v) in organic reactions, e.g. sulphonation, esterification, polymerization, condensation, etc. 81 IIB Q.10 (b)(i) Chlorine is prepared industrially by electrolysis of brine (conc. NaCl) . [1] Since two different kinds of cells are commonly in use, an answer to one of them is required. EITHER Diaphragm cell : [1] Graphite anode Cl - → 2 1 Cl 2 + e - [ ½ + ½ ] Steel net (or wire gauze) cathode H + + e - → 2 1 H 2 [ ½ + ½ ] Na + is also attracted to cathode. Essential feature that a diagram (usually asbestos) is inserted between the two electrodes to ensure that the chlorine evolved at the anode is not able to react with the solution of NaOH produced at the cathode. [1] OR Flowing mercury cell : (1) Graphite anode Cl - → 2 1 Cl 2 + e - ( ½ + ½ ) Mercury cathode Na + + e - → Na ( ½ + ½ ) Na form an amalgam with Hg. (1) (ii) Transportation : Chlorine is usually compressed to form liquid chlorine which is stored in steel cylinders for storage and transportation. [2] 1
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Section 10/ The p-Block Elements / Suggested solutions / (iii) Dry chlorine does not bleach. [1] The bleaching action is due to the hypochlorous acid (chloric(I) acid), HClO, [1] formed by the action of Cl 2 on water. HClO is unstable and losses oxygen .[ ½ ] Hence bleaching action is one of oxidation . [ ½ ] 82 IIB Q.8 (c) (i) NH 3 , NH 4 NO 3 , (NH 4 ) 2 SO 4 , (NH 4 ) 3 PO 4 , urea, etc. (Any four) [2] (ii) I. 4NH 3 + 5O 2 → 4NO + 6H 2 O (1) [1] (excess) If not excess, 4NH 3 + 3O 2 2N 2 + 6H 2 O (acceptable without equation) reduce yield. [1] II. If NH 3 /air mixture is too fast, reaction (1) not complete. [1]
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This note was uploaded on 08/17/2011 for the course CHEM 100 taught by Professor Fleet during the Fall '08 term at Oxford University.

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ALS10A - Section 10/ The p-Block Elements / Suggested...

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