SRJC_H1_CHEM_P1_Worked_Solutions

SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 1 CHEMISTRY 8873/01 JC2 Preliminary Examination 20 September 2018 Paper 1 Multiple Choice 1 hour 1 B 6 B 11 A 16 C 21 A 26 D 2 B 7 A 12 B 17 B 22 A 27 C 3 D 8 A 13 D 18 B 23 D 28 A 4 C 9 C 14 D 19 B 24 A 29 D 5 D 10 A 15 B 20 C 25 B 30 A WORKED SOLUTIONS 1 Use of the Data Booklet is relevant to this question. What is the number of atoms in 800 cm 3 of hydrogen gas under room temperature conditions? A 2.0 x 1022 B 4.0 x 1022 C 2.0 x 1025 D 4.0 x 1025 Ans: B nH= ଴.଼ ଶସ × 2 number of H atoms = ଴.଼ ଶସ × 2 × 6.02 × 10 ଶଷ ൌ 4.0 x 1022 2 Use of the Data Booklet is relevant to this question. The relative abundances of the isotopes of a sample of carbon are shown in the table below. What is the relative atomic mass of carbon in this sample? relative isotopic mass 12 13 14 relative abundance 100 1.08 0.01 A 12.00 B 12.01 C 12.10 D 12.15 Ans: B Relative atomic mass = ሺଵଶ ×ଵ଴଴ሻାሺଵଷ ×ଵ.଴଼ሻାሺଵସ ×଴.଴ଵሻ ଵ଴଴ାଵ.଴଼ା଴.଴ଵ = 12.01

3 Four substances E, F, G and H have physical properties as shown. substance melting point/ °C boiling point/ °C electrical conductivity of solid of liquid E 17 45 Poor Poor F 64 759 Good Good G 1132 1950 Poor Good H 3550 3825 Good Unknown What could be the identities of E, F, G and H? E F G H A PCl5 SO3 Na 2O Al2O3 B PCl5 A l2O3 K Na 2O C SO3 PCl5 C (graphite) Na 2O D SO3 K Na 2O C (graphite) Ans: D substance melting point/ °C boiling point/ °C electrical conductivity Structure of solid of liquid E 17 45 Poor Poor SMS PCl5 / SO3 F 64 759 Good Good GMLS K G 1132 1950 Poor Good GILS Na2O H 3550 3825 Good Unknown GMS Graphite

4 10 cm3 of hydrogen peroxide was diluted to 250 cm 3 using a standard flask. 25.0 cm 3 of the diluted solution was reacted with 10 cm3 of concentrated potassium iodide in the presence of dilute sulfuric acid. The resulting mixture was then titrated with 0.10 mol dm –3 sodium thiosulfate. It was found that 21.00 cm3 of thiosulfate was required to reach end-point. The following shows the reactions described above. H 2O2 + 2I– + 2H+ → I2 + 2H2O I2 + 2S2O32– → 2I– + S4O62– What is the initial concentration of the hydrogen peroxide used? A 0.04 mol dm–3 B 0.08 mol dm–3 C 1.05 mol dm–3 D 2.10 mol dm–3 Ans: C Mole ratio 2S2O32– : 1 I2 : 1H2O2 n S2O32– = ଶଵ.଴଴ ଵ଴଴଴ × 0 . 1 0 = 2.10 × 10–3mol n H2O2in 25 cm3 = 1.05 × 10–3 mol n H2O2in 250 cm3 = 1.05 × 10–2 mol initial concentration of H2O2 = 1.05 × 10–2 / (10/1000) = 1.05 mol dm–3 5 Which of the following is a redox reaction? A NaOH + HBr → NaBr + H2O B FeCl3 + 6H2O → [Fe(H2O)6]3+ + 3Cl– C H2SO4 + Ca(OH)2 → CaSO4 + 2 H2O D Cu + NH3 + O2 + H2O → [Cu(NH3)4](OH)2 A