NJC 2019 H1 Promo Paper 1 solutions

1 NJC Promotional Examination 8873/01/2019 [Turn over NJC 2019 H1 Chemistry Promo Solutions for P1 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. C C D A B C C A D D 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. C B A D A A D B B A 1 Use of the Data Booklet is relevant to this question. What is the number of atoms in 500 cm3 of oxygen under room conditions? A 1.25 × 1022 B 1.34 × 1022 C 2.50 × 1022 D 2.68 × 1022 Amount of O2 = 0.500 24 = 0.02083𝑚𝑜𝑙 No. of O atoms = 0.02082 (2)(6.02 × 1023) = 2.50 × 1022 Ans: C 2 Gallium nitride, GaN, could revolutionise the design of electric light bulbs because only a small length used as a filament gives excellent light at low cost. GaN is an ionic compound containing the Ga3+ ion. Which statements about GaN are correct? 1 The outer electronic configuration of Ga atom is 4s24p1 since Ga is a Group 13 element. 2 The electron arrangement of the nitrogen ion in GaN is 1s 2 2s2 2p3. 3 Ga3+ ion deflects less than Al3+ ion in an electric field. A 1 only B 2 only C 1 and 3 only D 2 and 3 only Statement 1: True Statement 2: N in GaN exists as N3–, electronic configurations 1s2 2s2 2p6 Statement 3: True. Angle of deflection α 𝐶ℎ𝑎𝑟𝑔𝑒 𝑠𝑖𝑧𝑒 . Ga3+ ion has same charge but large Ar than Al3+ ion. Hence Ga3+ ion deflects less Ans: C 3 Oxygen has two isotopes, 16O and 18O. An oxide ion, 𝑂8 𝑥 y–, has the same number of neutrons and electrons. What could be the values of x and y? x y Neutrons Electrons A 16 1 16-8 = 8 8+1 = 9 B 16 2 16-8 = 8 8+2 = 10 C 18 1 18-8 = 10 8+1 = 9 D 18 2 18-8 = 10 8+2 = 10 Ans: D

2 NJC Promotional Examination 8873/01/2019 [Turn over 4 Methyl mercaptan, CH3SH, is a substance often used to impart a smell to natural gas in a pipeline. The chemical equation for the combustion of CH3SH is as shown below. CH3SH + 3O2 → CO2 + SO2 + 2H2O A 10 cm3 sample of CH 3SH is exploded with 60 cm 3 of oxygen and the resultant gas mixture is passed into excess NaOH(aq). What is the percentage of the volume of the resultant gas mixture dissolved in NaOH? [All gas volumes are measured at room temperature and pressure.] A 40.0% B 28.5% C 20.0% D 14.3% CH3SH + 3O2 → CO2 + SO2 + 2H2O Vinitial / cm3 10 60 0 0 Vfinal / cm3 0 30 10 10 Both acidic CO2 + SO2 are absorbed by NaOH(aq)  % vol decrease = 20 50 × 100 = 40.0% Ans: A 5 Which sketch show the correct trend in the stated property for the elements in Period 3 of the Periodic Table? 1 atomic radius This graph shows the trend of the ionic radius instead. Atomic radius decreases across a period due to increase nuclear charges, but insignificant increase in shielding effect. 2 first ionisation energy This graph shows the correct trend of 1st IE’s of period 3 elements. Radius /nm Na Mg Al Si P S Cl First I.E. /