TJC_H1_CHEM_P1_Worked_Solution

1 2017 JC2 Prelim H1 CHEMISTRY MCQ Worked Solution 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 B C A B A D B D D D D B B C A 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 C A C A B B A C A C D A D B C 1 Answer: B Since Ba(NO3)2  N2, Mr of Ba(NO3)2 = 261.3 No. of moles of N 2 = No. of moles of Ba(NO 3)2 = 1 261.3 = 3.83 x 103 mol Volume of N2 = 3.83 x 103 x 24000 = 91.8 cm3 2 Answer: C Definition – Relative molecular mass is the average mass of one molecule of an element or compound on a scale on which one atom of the 12C isotope of carbon has a mass of 12 units. A is incorrect. Relative molecular mass is a ratio. B is incorrect. It should be the ratio of the average mass of a molecule to 1/12 the mass of a 12C atom. C is correct. D is incorrect. It is the mass of one mole of molecules on a scale where one mole of 12C atoms has a mass of 12 units. 3 Answer: A NH3 + H2O  NO + 5H+ + 5e x4 4e + 4H+ + O2  2H2O x5 4NH3 + 4H2O + 5O2  4NO + 10H2O 4NH3 + + 5O2  4NO + 6H2O 4 Answer: B Positively charged particles deflected towards negative electrode Angle of deflection α 𝐶ℎ𝑎𝑟𝑔𝑒 𝑀𝑎𝑠𝑠 20 𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝑑𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝐻𝑒2+ = +1 1 +2 4 Angle of deflection He2+ = +10 5 Answer: A A. Disproportionation (self-redox) reaction. Oxidation state of O changes from -1 in MO2 to -2 in MO and 0 in O2, B. O22- contains 8+8+2 = 18e C. lattice energy ∞ (q+q-/r+ + r -) In this case, only r – is different. Since peroxide ion, O22- is bigger than oxide ion, O2- the lattice energy of MO2 is smaller than MO. D: The dot -and-cross diagram of the anion should be 6 Answer: D A: Ethene is a planar molecule which has all atoms on the plane B: Tri-iodide has 3 lone pairs and 2 bond pairs, hence the ion is linear and all atoms lie on the same plane C: XeF4 has 4 bond pairs and 2 lone pairs, hence shape is square planar and all atoms lie on the same plane D: BeCl42- has a total of 4 bond pairs (2 covalent bonds and 2 dative bonds) around Be atom. The shape is tetrahedral. 7 Answer: B A: HF has hydrogen bonding between its molecules and hence require a larger energy to overcome compared to pd-pd between HI molecules. B: MgO has a higher boiling point. MgO has a higher lattice energy than NaCl due to larger charge and smaller ionic radii of Mg2+ and O2- ion compared to Na+ and Cl-. C: SiH4 has a higher boiling point as its Mr is larger than CCl4 and thus the id -id interactions are str onger and more extensive than CH4. D: trans-C2H2Cl2 has a lower boiling point as it has no net dipole moment so the molecule is non-polar and only has id-id interactions between the molecules. cis-C2H2Cl2 has pd-pd interaction between the molecules and more energy is needed to overcome the stronger pd -pd interactions. 8 Answer D Dipoles are present due to the difference in electronegativity between oxygen and hydrogen atoms. There are is a net dipole hence water