2013_MJC_H1_Chemistry_P2 Mark_scheme

1 ©MJC Chemistry 2013 MJC H1 Suggested Answers   Section A: Structured Questions 1(a) (i) Perc entage abundance of Te-130 = 34.48 Isotopic mass x % abundance of Te-128 = 4069 Isotopic mass x % abundance of Te-130 = 4482 Relative atomic mass of Te = 127.7 (ii) There is inter-electron repulsion between the paired electrons in the 5p orbital of Te. (b) (i) (ii) There are 4 bond pairs and 1 lone pair around Te atom. To minimise repulsion, the 5 electron pairs are directed to the corners of a trigonal bipyramid. Since lone pair-bond pair repulsion > bone pair-bond pair repulsion, the shape of TeCl 4 is distorted tetrahedral. (iii) Te has empty and energetically assessible 5d orbitals to accept electrons and expands its octet structure. (c) TeC l4 undergoes complete hydrolysis to form strongly acidic solutions with pH= 2 TeC l4 + 2H2O → TeO2 + 4HCl AlCl3 undergoes hydration and slight hy drolysis to form an acidic solution with pH=3.0 AlCl 3 (s)  OH 2 Al3+ (aq) + 3Cl- (aq) [Al(H2O)6]3+ [Al(H2O)5(OH)]2+ + H+ Te xx xx xx x Cl x xx xx xx Cl x xx xx xx Cl xx xx x xx Cl

2 ©MJC Chemistry 2(a) (i) W. It has the highest q r   value (ii) V (or Cr or W) (b) Adding carbon atoms into th e space between the iron atoms in the lattice will prevent the ir on atoms from sliding ov er each other easily and hence do not go out of shape easily. (c) Cr forms an oxide layer and pr events oxygen from reacting with the iron. (d) Metallic bonds are strong electrostatic forces of attraction between the cations and sea of delocalised electrons in a giant metallic lattice structure. (e) (i) FeO 4 2- -0.4 to -0.6V (ii) 6e + 5H 2O + 2FeO4 2-  Fe2O3 + 10OH (f) (i) No of moles of I-= 1.293 x 10-2 No of mole of Fe 3+ = 1.29x 10-2 (ii) x = 3. (iii) +2 and +3 + e  e e e e   e e  e e metal cations + + + + + + + ++++ + + + + delocalised electrons

3 ©MJC Chemistry (g) Ea is lowered due to an alternative reaction pathway. Number of reactant particles with E ≥ Ea increases. Frequency of effective collisions increases. Rate of reaction is proportional to frequency of effective collisions. 3(a) Reagent Compound A, B or C Structural formula of the organic product Na2CO3 (aq) C CH=CHCH3 COO-Na+

4 ©MJC Chemistry 2,4-DNPH A CH=CHC H N N H NO2 O2N Tollens’ reagent A CH=C H C O O- (b)(i) CH I 3 (ii) COOH COOH

5 ©MJC Chemistry (c)(i) (ii) Step I HCN Conditions: trace amount of NaOH or NaCN, cold Step II Dilute H 2SO4 heat (d) CHO CHOH CHOH CHOH CHOH CH2OH H O H Hydrogen bonding Section B: Free Response Questions C 4(a) Standard