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MJC_H2_CHEM_P4_Suggested_Ans.pdf

MJC_H2_CHEM_P4_Suggested_Ans.pdf - 2017 MJC H2 Chemistry...

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2017 MJC H2 Chemistry Prelim P4 Suggested Answers MJC Prelim 2017 H2 Chemistry 1 MERIDIAN JUNIOR COLLEGE JC 2 Preliminary Examination H2 Chemistry Paper 4 ________________________________________________________________________ 1 (a) Procedure Burette readings Final burette reading / cm 3 48.00 Initial burette reading / cm 3 0.00 Volume of FA 2 / cm 3 48.00 Mass Readings Mass of weighing bottle and FA 1 / g 6.789 Mass of weighing bottle and residual solid / g 4.789 Mass of FA 1 added / g 2.000 Titration 1 2 Final burette reading / cm 3 21.30 21.30 Initial burette reading / cm 3 0.00 0.00 Volume of FA 3 / cm 3 21.30 21.30 (b) Average volume of FA3 used = 21.30 + 21.30 2 = 21.30 cm 3 (c) (i) Amount of HC l in FA3 in 21.30 cm 3 = 25.0 × 0.2 1000 = 5.00 x 10 -3 mol (ii) Amount of HC l remaining in FA3 (in 250 cm 3 ) = 3 250 × 5 10 17.50 = 0.0587 mol (iii) Initial amount of HC l = 48.00 × 2.0 1000 = 0.0960 mol Amount of HC l in FA3 that has reacted = 0.0960 – 0.0587 = 0.0373 mol
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2017 MJC H2 Chemistry Prelim P4 Suggested Answers 2 MJC Prelim 2017 H2 Chemistry (iv) Amount of MgCO 3 = 0.0373 2 = 0.01865 mol Mass of MgCO 3 = 0.01865 x (24.3 + 12 + 48) = 1.57 g Percentage purity of FA1 = 1.57 100 % 2.00 = 78.6% (d) (i) smallest volume used = ……………………………………. largest volume used = ……………………………………. (ii) The percentage purity of FA 1 should be the same for student X and student Y since FA2 (hydrochloric acid) is added in excess to completely react with FA1 (magnesium carbonate). 2 Results Expt Volume of FA 5 / cm 3 Volume of FA 6 / cm 3 T FA5 / o C T FA6 / o C T weighted initial / o C T max / o C T / o C 1 10.0 40.0 28.0 32.0 31.2 34.5 3.3 2 20.0 30.0 30.0 32.0 31.2 38.0 6.8 3 30.0 20.0 31.0 31.5 31.2 41.0 9.8 4 40.0 10.0 31.0 31.5 31.1 35.5 4.4 5 15.0 35.0 29.5 31.5 30.9 36.0 5.1 6 25.0 25.0 30.5 31.5 31.0 40.0 9.0 7 35.0 15.0 31.0 31.5 31.2 38.0 6.8 [5] 48.40 cm 3 48.60 cm 3
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