SAJC_H2_CHEM_P1_WORKED_SOLUTIONS

1 [Turn Over 1. A solid hydrocarbon was completely combusted in a closed vessel at 120 oC. The residual gas had a volume of 64 cm 3, which decreased by 24 cm 3 after bubbling through a dehydrating agent. After this, 40% of the final gas volume consisted of oxygen. What is the empirical formula of the hydrocarbon? A CH B CH2 C CH3 D C2H3 Vol of H2O = 24 cm3 Vol of CO2 = 0.6 x (64 – 24) = 24 cm3 Mole ratio of CO2 : H2O = 24 : 24 = 1 : 1 Mole ratio of C : H in CxHy = 1 : 2 2. When cobalt metal is reacted with a solution containing cobalt( III) ions, cobalt( II) ions are formed. How many moles of Co and Co 3+(aq) would result in a mixture containing both cobalt(II) and cobalt(III) ions in the mole ratio of 3:1 after the reaction had taken place? Moles of Co Moles of Co3+ A 1 2 B 1 3 C 1 5 D 2 3 Co + 2Co3+  3Co2+ I 1 3 0 (Co3+ was in excess) C -1 -2 +3 F 0 1 3

2 [Turn Over 3. Which graph does not share the same general shape with the other three graphs according to the ideal gas law for a fixed mass of gas? A pV against p (at constant T) pV = nRT At constant T, pV = constant B V/T against T (at constant p) pV = nRT At constant p, = constant C p against V (at constant T) pV = nRT At constant T, D pV against V (at constant T) pV = nRT At constant T, V/T T V

3 [Turn Over 4. Which element will possess an empty s orbital after forming a singly-charged cation? A Barium Ba+: [Xe]6s1 B Vanadium V+: [Ar]3d34s1 C Copper Cu+: [Ar]3d10 D Gallium Ga+: [Ar]4s2 5. Which of the following reactions will form a product with the same shape as the reactant with respect to the underlined element? A 2AlCl3  Al2Cl6 Trigonal planar to Tetrahedral B 2H2O2  2H2O + O2 Bent to Linear C PCl3 + Cl2  PCl5 Trigonal pyramidal to Trigonal bipyramidal D CH3CH2CHO + [O]  CH3CH2COOH Trigonal planar to Trigonal planar 6. Which of the following is arranged correctly in the order of decreasing melting points? A Sulfur > Chlorine > Argon S8 has the largest electron cloud, followed by C l2 and Ar, hence it has the most extentive id-id interactions. B Carbon dioxide > Silicon dioxide > Germanium dioxide Silicon dioxide (giant covalent structure) should have a higher m.p than carbon dioxide (simple covalent structure). C Beryllium chloride > Magnesium chloride > Calcium chloride Beryllium chloride (simple c ovalent structure due to high charge density of Be 2+) should have a lower m.p than magnesium chloride. D Sodium > Magnesium > Aluminium Al has the largest no. of delocalised electrons, followed by Mg and Na, hence it has the strongest metallic b