AJC_H1_CHEM_P1 P2 ANS

Anderson Junior College 2009 H1 Chemistry Preliminary Examinations Paper 2 Mark Scheme 1 (a) Empirical formula is the simplest formula that shows the relative number of atoms of each element present in a compound. (b) (i) CH2 (ii) CnH2n + 2 3 n O2  n CO2 + n H2O Volume of H2O = 40 cm3 Mole ratio of H 2O : CnH2n = n : 1 = 40 : 10 Hence n = 4 Molecular formula of A is C 4H8. (c) CC CH3 H H3C H CC H CH3 H3C H A B CC CH3 CH3 H H CC H CH2CH3 H H C D A (or B), C a nd D are structural isomers. A and B are cis-trans isomers. 2 (a) (i) Let the rate equation be rate = k [CH3COCH3]x [I2]y [H+]z As observed from the graph, rate of reaction remains constant when [I2] changes => rate of reaction is independent of [I2] => zero order wrt [I2], y = 0 Using the 1 st graph, when [H+] doubled while [CH3COCH3] is constant,  z 0.006 0.10240 ()0.006 0.20 120 z = 1

Using the 2 nd graph, when [CH 3COCH3] increased by 1.5 times while [H +] is constant,  x 0.006 0.10240 ()0.006 0.15 160 x = 1 (ii) rate = k [CH3COCH3] [H+] 0.006 120 = k (0.10)(0.20)  k = 2.50 X 10 –3 mol–1 dm3 min–1 (iii) Hydrogen ions speed up the rate of the reaction by providing a different reaction path which has lower activation energy. As shown on the diagram, the number of reactant molecules with energy greater than or equal to the activation energy (E a’) will increase. This results in an increase in the frequency of effective collisions. Hence, the rate of reaction increases. (b) : I2 molecule Simple molecular lattice structure with weak van der Waals forces of attraction between I2 molecules. (c) NaOH(aq), warm Yellow precipitate observed for propanone but not propanal Represents no. of molecules with energy greater or equal to Ea (uncatalysed) Number of molecules with energy < Represents no. of molecules with energy greater or equal to Ea’ (catalysed) Energ y Ea Ea’

3 (a)  Silicon has the highest melting point, followed by magnesium, then sulfur.  Magnesium has a giant metallic structure with strong electrostatic attraction between magnesium ions and delocalized electrons.  Silicon has a giant macromolecular structure with strong and extensive covalent bonds between silicon atoms.  Sulfur has a simple molecular structure with weak van der waals’ forces of attraction between the molecules. (b) (i) Maximum temperature reached = 54.5 0C [1] Maximum Temperature reached = 54.5 oC