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    May 2018
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  1. Paper 1, November 2015, and TZ0
  2. Which element forms more than one stable positive ion? A. Ca B. Cr C. Zn D. Ba The answer is B, but how? Thanks!
  3. Which compound can both be esterified and turn acidified potassium dichromate (VI) solution green? A. (CH3)3COH B. CH3CH2CO2H C. (CH3)2CHOH D. CH3CH2COCH3 The answer is C, but how? Thanks!
  4. Which molecule is non-polar? A. OF2 B. NH3 C. BF3 (answer) D. SO2 How do we know this without using the electronegativity values? Thanks!
  5. The graph below illustrates how the vapour pressures of ethoxyethane, CH3CH2OCH2CH3, benzene, C6H6, and water, H2O, change with temperature. Using data from the graph, explain the difference in vapour pressure of ethoxyethane, benzene and water at 30 °C. ANSWER: water has hydrogen bonding; benzene has van der Waals’/London/dispersion forces; ethoxyethane has dipole–dipole forces (and van der Waals’/London/ dispersion) but they are weaker than benzene I understand the forces of each of these substances BUT how does it relate to their positions on the graph? Thanks!
  6. Bromine was added to hexane, hex-1-ene and benzene. Identify the compound(s) which will react with bromine in a well-lit laboratory. Answer (according to markscheme): hexane AND hex-1-ene; Accept "benzene AND hexane AND hex-1-ene" I thought that the answer would be hex-1-ene and benzene as hexane is saturated (the bromine water test). Why is it not?
  7. Does the number of delocalized electrons equal the number of valence electrons for an atom? Thank you!
  8. On the IB Chemistry Syllabus (or any experimental science for that matter), there is a section that is titled "Utilization". It just refers to other practical links to the concepts in each chapter. Are we supposed to know these links for the actual exam? Thanks!
  9. What is the approximate pH of a 0.01 mol dm–3 ammonia solution? A. 2 B. More than 2 but less than 7 C. More than 7 but less than 12 D. 12 The correct answer is C. I know that A and B cannot be the answers but how would you do this question without actually doing the math as the answer could be C or D?
  10. The diagrams below represent equilibrium mixtures for the reaction Y + X2 ->/<- XY + X at 350 K and 550 K respectively. Deduce and explain whether the reaction is exothermic or endothermic. (350 K VS. 550 K) Thank you in advance!
  11. Attached is the question. The answer is C, but I do not know why. Thank you! http://www.easynotecards.com/print_list/21945?fs=2&dis=1&pi=on
  12. The reaction below represents the Haber process for the industrial production of ammonia. N2(g) + 3H2(g) 2NH3(g) ∆HO = –92 kJ The optimum conditions of temperature and pressure are chosen as a compromise between those that favour a high yield of ammonia and those that favour a fast rate of production. Economic considerations are also important. Which statement is correct? A. A higher temperature would ensure higher yield and a faster rate. B. A lower pressure would ensure a higher yield at a lower cost. C. A lower temperature would ensure a higher yield and a faster rate. D. A higher pressure would ensure a higher yield at a higher cost. The answer is D. I know that it is either C or D. I'm assuming it is D because only catalysts are responsible for increasing the rate but there is no such mention in this question. Is my reasoning correct?

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