2025 ASRJC Prelim H2Chem P2_MS

9729/02/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2025 JC 2 PRELIMINARY EXAMINATION PAPER 2 SUGGESTED SOLUTIONS NAME:______________________________ ( ) CLASS: 25 / _____ (a) Mild steel is an alloy that contains iron and carbon. A sample of mild steel was analysed, and four different types of atoms were identified; A, B, C and D. Table 1.1 shows information about the four types of atoms found in the sample. Table 1.1 atom relative mass relative % abundance A 12.00 0.238 B 13.00 0.012 C 53.94 5.79 D 55.93 93.96 (i) Calculate the relative atomic mass of carbon in this sample to four significant figures. Show your working. [1] Relative atomic mass of carbon = 12×0.238 + 13×0.012 0.238 + 0.012 = 12.05 [1] (ii) In an experimental set -up, beams of particles travelling at the same speed from different sources are subjected to an electric field as shown in Fig. 1.1. A beam of protons with an angle of deflection of 60° has already been drawn. + protons Fig. 1.1 Under identical conditions, beams of particles 12C2+ and 56Fe2+ were subjected to the same electric field. Calculate the angle of deflection of 12C2+ and 56Fe2+particles under the electric field and sketch the beams of 12C2+ and 56Fe2+ on Fig. 1.1. Label the beams clearly. [2] Angle of 12C2+ = 2 12 x 60o = +10.0o Angle of 56Fe2+ = 2 56 x 60 = +2.14o [1] for both [1] for both beams 12C2+ 56Fe2+

(b) The compound C6H6 has many possible structural isomers. Three suggested structures of C6H6 are shown in Fig. 1.2. Kekulé benzene Dewar benzene Ladenburg benzene Fig. 1.2 (i) Using Fig. 1.2, complete Table 1.2 to predict the number of carbon atoms that have sp, sp 2 and sp 3 hybridisation in Kekulé benzene, Dewar benzene and Ladenburg benzene. Table 1.2 C6H6 structure sp hybridised sp2 hybridised sp3 hybridised Kekulé benzene Dewar benzene Ladenburg benzene [2] [1] row 1 and 2 correct; [1] row 3 correct (ii) Dewar benzene contains both  bonds and  bonds. By reference to the hybridrisation of the carbon atoms and orbital overlap, describe the covalent bonding in Dewar benzene. [2]  bonds: [1] • Head-on overlap of the sp2 orbital of C with sp2 orbital of adjacent C • Head-on overlap of sp3 orbital of C with sp3 orbital of adjacent C • Head-on overlap of sp2 orbital of C with sp3 orbital of adjacent C • Head-on overlap of the sp2 orbital of C with the s orbital of H • Head-on overlap of the sp3 orbital of