JJC_H1 Chemistry 8872_H1 Prelim Paper 2 Ans

JJC Chemistry H1 P2 Answers 1. (a) (i) Amount of Cl2 in 1 cylinder = 0 . 71 170000000 / 5730 = 4.18 x 102 mol [1] (ii) Conc. of Cl2 in g dm–3 = mg g dm mg 1000 1 11000 3 × × = 1 Conc. of Cl2 in mol dm–3 = 0 . 71 1 = 0.0141 mol dm–3 [1] (a) (iii) Volume of factory room = 3 3 3 3 10 1 125 m dmm −×× = 25 000 dm3 Conc. of Cl2 in the factory = 25000 10 18 . 42× = 0.0167 mol dm–3 0.0167 mol dm–3 > 0.0141 mol dm–3 / lethal conc [2] (b) (i) C O Cl Cl 120o [1] (ii) sp2 [1] (iii) Phosgene contains both σ bonds and π bonds. Explain the terms in italics, drawing diagrams to show these bonds clearly. State the number of σ bonds and π bonds in phosgene. A sigma bond (σ bond) is formed by head-on overlap of orbitals. A pi bond (π bond) is formed by side-way overlap of orbitals. Phosgene has 3 σ bonds and 1 π bond. (iv) Both phosgene and chlorine have simple covalent / molecular structure Higher amount of energy is required to overcome the stronger permanent dipole – permanent dipole attraction / van der Waals’ forces of attraction/ intermolecular forces between phosgene molecules than weaker in induced dipole – induced dipole attraction / van der Waals’ for ces of attraction/ intermolecular •• π bond σ bond Page 1 of 12

forces between chlorine molecules. OR Phosgene has a larger size of electron cloud / no. of electrons than chlorine . Higher amount of energy is stronger permanent dipole – permanent dipole attracti on / van der Waals’ forces of attraction/ intermolecular forces between phosgene molecules than weaker in induced dipole – induced dipole attraction / van der Waals’ forces of attraction/ intermolecular forces between chlorine molecules. Thus phosgene has a higher boiling point than chlorine. [2] [Total: 11] 2. (a) The 1st IE of an element E is the energy required to remove one mole of electrons from one mole of gaseous E atoms. [1] (b) [1] (c) Explain the difference between the first ionisation energy of (i) carbon and nitrogen 6C: 1s2 2s2 2p2 7N: 1s2 2s2 2p3 N has a smaller atomic radius than C and N has a larger nuclear charge than C while shielding effect by the inner shell electrons is relatively constant for both elements. Hence 1 st IE of N is higher than that of C. [1] (ii) nitrogen and oxygen proton number First ionisation energy (kJ mol−1) 5 Li Be B C N O F Ne Li Be B C N O F Ne 0 10 Page 2 of 12

N: 1s2 2s2 2p3 O: 1s2 2s2 2p4 Mutual repulsion between the paired 2p electrons in O makes it easier to remove one of the paired electrons compared to removing the unpaired 2p electron of P which does not experience such repulsion. Hence 1st IE of O is lower than that of N. [1] [Total: 4] (i) [acetylsalicylic acid]= 1000 0 . 25 200 . 01000 20 × = 0.160 mol dm–3 [1]3. (a) (ii) [H+] = 10-2.8 = 1.58