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1. You are given the following molecules: PCl 3 , PCl 5 , HOF

1. You are given the following molecules: PCl 3 , PCl 5 , HOF (a) For each of these molecules, draw its three-dimensional structure. (3 marks) (b) Name the three-dimensional structures in (a). (3 marks). All of these are wrong answers!!!. Note P.7.

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1. You are given the following molecules: PCl 3 , PCl 5 , HOF

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  1. 1. You are given the following molecules: • PCl3, PCl5, HOF • (a) For each of these molecules, draw its three-dimensional structure. (3 marks) • (b) Name the three-dimensional structures in (a). (3 marks) All of these are wrong answers!!!

  2. Note P.7 PCl3 – 3bond pairs --1 lone pair

  3. 1. You are given the following molecules: • PCl3, PCl5, HOF • (a) For each of these molecules, draw its three-dimensional structure. (3 marks) • (b) Name the three-dimensional structures in (a). (3 marks) HOF– 2bond pairs --2 lone pairs PCl3 – 3bond pairs --1 lone pair PCl5 – 5bond pairs --0 lone pair

  4. 1. You are given the following molecules: • PCl3, PCl5, HOF • (a) For each of these molecules, draw its three-dimensional structure. (3 marks) • (b) Name the three-dimensional structures in (a). (3 marks) PCl3 – 3bond pairs --1 lone pair PCl5 – 5bond pairs --0 lone pair HOF– 2bond pairs --2 lone pairs Draw a 3D structure of CSH2

  5. (c)(i) The polarity of a molecule can be explained by the concept of electronegativity. • What is meant by “electronegativity”? (1 mark)

  6. (c)(ii) Describe the trend in electronegativity of elements in period 2 of the Periodic Table. (1 mark) P.12

  7. (d) Which one, PCl3 or PCl5, is a polar molecule? Explain your answer. (2 marks) PCl3 is a polar molecule which consists of 3 polar P-Cl bonds arranged in trigonal pyramidal shape. [1] The polarities of the polar bonds cannot cancel out each other. [1] XPolarities of the polar bonds in PCl3 are not identical (They are identical!!!) X 3 polar P-Cl bonds are arranged asymmetrically/symmetrically. (Don’t mention this when it is a polar molecule) But this explanation is necessary for a non-polar molecule e.g1 . PCl5is a non-polar molecule which consists of 5 polar P-Cl bonds arranged in trigonalbipyramidal shape symmetrically.[1] The polarities of the polar bonds cancel out each other. [1] e.g2 . COS is a non-polar molecule….

  8. 2.A student studied the effect of electric field on a jet of propanone by using a positively • charged rod. The structure of propanone is shown below. • (a) What would be observed if a positively charged rod was placed near the jet of propanone? Explain your observation. (1 mark) The propanone liquid is deflected. [0.5]The negative ends of the polar molecules are attracted to the positively charged rod. [0.5] X The jet / solution is deflected. X The negative ions of the molecules are attracted to the positively charged rod. X The molecule is polar.

  9. (b) Describeand draw a diagram to show how a propanone molecule forms hydrogen bonds with water molecules. (2 marks) P.24 The electrostatic attractions exists between the partial positively charged H atom of water and the lone pair of electrons on O atom of propanone. [1]

  10. (c)Two reagent bottles labelled A and B are left unattended on the bench. It is known that one bottle contains pure propanonewhile the other contains a mixture of propanone and water. Bottle B gives a stronger smell of propanonewhen the caps of the two bottles are opened. • (i) Which bottle contains a mixture of propanone and water? (1 mark) • (ii)Explain your answer in (c)(i) in terms of intermolecular forces. (2 marks) Book 2 Ch 17 E15 2.(c)(i) Bottle B. [1] 2.(c)(ii) When propanonedissolves in water, [1] propanoneforms hydrogen bonds with water molecules. [ 1} it gives the strong smell.

  11. The table below shows three carbon compounds. Arrange the three compounds in order of increasing boiling point. Explain your answer. (4 marks) VDW forces H-Bond (2H-bonds) / size larger VDW forces /chain H-Bond (1 H-bond) / size smaller VDW forces / branched All of these are wrong answers!!!

  12. The table below shows three carbon compounds. Arrange the three compounds in order of increasingboiling point. Explain your answer. (4 marks) branched /size smaller / size larger chain All of these are wrong answers!!!

  13. The table below shows three carbon compounds. Arrange the three compounds in order of increasing boiling point. Explain your answer. (4 marks) Butane<Propanone<Propan-1-ol[0.5] For all the 3 compounds, there are van der Waal’s forces between molecules. [0.5] Propan-1-ol has the highest boiling point because it can form hydrogen bonding between its molecules. [1] The strength of hydrogen bonding is stronger than van der Waal’s forces. [0.5] Propanoneis polar and butane is non-polar, [1] van der Waal’s forces between a polar molecules is higher than that between non-polar molecules, [0.5]so propanone has a higher boiling point than butane.

  14. 3. Chlorine can be made by reacting concentrated hydrochloric acid with potassium permanganate solution. • 2KMnO4(aq) +16HCl(aq)  2MnCl2(aq) + 2KCl(aq) + 5Cl2(g) + 8H2O(l) • (a) Is the above reaction a redox reaction? Explain your answers in terms of the oxidation number.(2 marks) • (b) Deduce which species is an oxidizing agent. (1 mark) 3.(a)Yes. The oxidation number of Mn in KMnO4 decreases from +7 to +2. KMnO4 is reduced. [1] The oxidation number of Cl in HClincreases from -1 to 0. HCl is oxidized. [1] 3.(b) KMnO4./ MnO4-[1] P.1

  15. 4. Magnesium oxide is insoluble in water, so it is difficult to titrate directly. Its purity can be determined by performing the following steps. • Step 1: 4.06 g of impure magnesium oxide was completely dissolved in 100 cm3 of 2.00M • hydrochloric acid in excess. • Step 2: The solution formed is then diluted to 250.0 cm3by distilled water. • Step 3: 25.0 cm3 of the dilute solution is titrated 0.02M sodium hydroxide solution. 19.7 cm3 of sodium hydroxide is required for the neutralization. • (a) Write a chemical equation with state symbols for the reaction in Step 1. (1 mark) • (b) Describe how you can perform dilution in Step 2 by using suitable apparatus. (3 marks) • (c) Suggest a suitable indicator for the titration in Step 3, and give the colour change at the end-point. (1 mark) 4.(a) MgO(s) + 2HCl(aq)  MgCl2(aq) + H2O (l) [1/0] 4.(b) X Use a pipette to transfer the solution to the 250.0 cm3 volumetric flask √(good) wash the 250.0cm3 volumetric flask with distilled water first. Pour all the solution obtained from Step 1 to a (250.0 cm3) volumetric flask. [1] Rinse all the solution left in the beaker by distilled water and transfer the washing to the volumetric flask. [1] Adddistilled waterto the graduation mark of the volumetric flask [0.5]and shake the volumetric flask thoroughly. [0.5] 4.(c) methyl orange[0.5], red to orange[0.5]/ (HCl add to NaOH) phenolphthalein, colourless to pink.

  16. P.28 P.30 Describe how can we dilute 1M HCl to 0.04M

  17. P.26

  18. 4. Magnesium oxide is insoluble in water, so it is difficult to titrate directly. Its purity can be determined by performing the following steps. • Step 1: 4.06 g of impure magnesium oxide was completely dissolved in 100 cm3 of 2.00M • hydrochloric acid in excess. • Step 2: The solution formed is then diluted to 250.0 cm3by distilled water. • Step 3: 25.0 cm3 of the dilute solution is titrated 0.02M sodium hydroxide solution. 19.7 cm3 of sodium hydroxide is required for the neutralization. • (d) Calculate the number of moles of hydrochloric acid added to the magnesium oxide. (0.5 mark) • (e) Calculate the number of moles of hydrochloric acid reacting with the magnesium oxide. (1.5 marks) • (f) Calculate the percentage purity of the magnesium oxide. (2 marks) 4.(d) 2 x 0.1 =0.2 mol[0.5] 4.(e) NaOH(aq) + HCl(aq) NaCl(aq) + H2O (l) no. of moles of NaOH in titration = 0.02 x 19.7/1000 = 0.000394 no. of moles of HCl in titration = 0.000394 no. of moles of 250 cm3HCl = 0.000394 x10= 0.00394 [0.5] no. of moles of HCl reacting with MgO = 0.2 -0.00394 =0.19606 [1] 4.(f) MgO(s) + 2HCl(aq)  MgCl2(aq) + H2O (l) no. of moles of MgO = 0.19606 /2 =0.09803 mass of MgO= 0.09803 x 40.3 =3.95g [1] % purity = 3.95/4.06 x100% =97.3% [1]

  19. (g) What compounds could be present in the magnesium oxide that could lead to a false value of its purity? Explain. (2 marks) Mg(OH)2 from MgO + H2O OR MgCO3from the original mineral source, (1) both of these compounds react with acid (1)and would lead to a false titration value. XMgO formed X Mg

  20. 5 (a)(i)Write a chemical equation with state symbols for the reaction between nickel and concentrated sulphuric acid. (1 mark) (ii)What property of concentrated sulphuric acid is responsible for the reaction in test tube A? (0.5 mark) (iii)State an observable change in test tube A. (1 mark) 5.(a)(i) Ni (s) + 2H2SO4 (l) NiSO4(s) + SO2(g) +2H2O (l) [1] 5.(a)(ii) oxidizing. [0.5] 5.(a)(iii) colourless gas bubbles can be seen. [1] X Ni dissolves, solution turns from colourless to green. iron(III) sulphate solution

  21. (b)(i)State an observable change in test tube B. (0.5 mark) (ii)Write an ionic equation for the reaction involved in test tube B. (1 mark) (c) Reagent X in test tube C was used to absorb any excess sulphur dioxide. Suggest what X could be. (1 mark) 5.(b)(i) solution turns from yellow to green. [0.5] 5.(b)(ii) 2H2O (l) +SO2 (g) + 2Fe2+(aq) SO32- (aq) + 2Fe3+ (aq) + 4H+ (aq) [1] 5.(c) sodium hydroxide solution. [1] (acid base: SO2 + 2NaOH  Na2SO3 + H2O) Limewater/ Ca(OH)2solution[1] ] (acid base: SO2+ 2Ca(OH)2 CaSO3+ H2O) / Acidified KMnO4 solution (redox :SO2 SO42- and MnO4-  Mn2+ ) X anhydrous CaCl2 X water iron(III) sulphate solution

  22. voltmeter chromium rod iron rod salt bridge iron(II) sulphate solution chromium(III) chloride solution X 2Cl- Cl2 + 2e- X 7H2O + 2Cr3+ Cr2O72- + 14H+ + 6e- • (2e + Fe2+  Fe) • 6(a) As times goes by, the colourof iron(II) sulphate solution in the beaker gradually fades out. State, with explanation, the direction of electron flow in the external circuit. (2 marks) • Electron flow from chromium to iron in the external circuit. [1] • Fe2+is reduced to form Fe, [0.5] so the concentration of Fe2+decreases[0.5], so the colour fades out. • X Cr is more reactive than Fe

  23. (b) Write the half equation for the change occurring at the chromium rod. (1 mark) • (c) Write the half equation for the change occurring at the iron rod. (1 mark) • (d) Which metal rod is an anode? Explain. (1 mark) • (e) State two functions of the use of salt bridge. (2 marks) • (f) Suggest why calcium nitrate solution cannot be used for making the salt bridge. (1 mark) • (g)Suggest an appropriate chemical for making the salt bridge. (1 mark) 6.(b) Cr(s) Cr3+ (aq)+ 3e-[1] 6.(c) Fe2+(aq) +2e- Fe(s) [1] 6.(d) Chromium rod. Oxidation occurs at chromium rod. [1] 6.(e) To complete the circuit by allowing ions to pass from one half cell to another. [1] To reduce excess charges building up in the half cells by providing ions to it. [1] 6.(f) It can react with sulphate ions and form insoluble CaSO4which blocks the salt bridge. [0.5] , the voltage of the cell drops to 0 quickly.[0.5] 6.(g) saturated KNO3 / NaCl/ NaNO3solution. [1] X Ca2+ P.22

  24. Electrons flow from X to Cu Reactivity: X>>Cu Electrons flow from Y to Cu Reactivity: Y>Cu • 7(a) What is the function of the lemons in these cells? (1 mark) • XXX act as a salt bridge • Act as an electrolyte. • 7(b) Arrange metal X, metal Y, and copper in increasing order of reducing power. (power of reducing other chemicals ) (1 mark) • Cu > Y > X

  25. P.16 Use of salt bridge : when there are 2 electrolytes (solutions) which need to complete the circuit P.11

  26. Electrons flow from X to Cu Reactivity: X>>Cu • 7(c) For Cell 1, write the half equation for the change that occurs at copper strip. (1 mark) • X Cu2+ + 2e- Cu • 2H+(aq) +2e- H2(g)

  27. 7(d) Suggest a reason to explain why the voltages of both Cell 1 and Cell 2 drop quickly. (1 mark) • X and Y can react directly with acid in lemon and produce hydrogen gas. Less electrons passes to the wire, which lower the efficiency of the cell.[1] / gas bubbles built up at Cu strip, which hinder the reaction of H+ to gain electron and the increases to resistance of the cell. • XX and Y can react directly with acid in lemon, gas bubbles built up at X and Y. • X lemon will use up. • X direct reaction of Cu and acid in lemon. • XX and Y dissolves • X H2 formed block the ions move from X  Cu

  28. 8. Hydrogen peroxide (H2O2) is another oxide of hydrogen. What is the oxidation number of oxygen in hydrogen peroxide? (1 mark)

  29. b) In the presence of a dilute sodium hydroxide solution, hydrogen peroxide reduces iron(III) ions and it is oxidized to oxygen. Write the half equation for the oxidization of hydrogen peroxide. (1 mark)  State the expected observation and write a chemical equation for the reaction involved. (2 marks) Redox Quiz (WS. P4)

  30. b) In the presence of a dilute sodium hydroxide solution, hydrogen peroxide reduces iron(III) ions and it is oxidized to oxygen. Write the half equation for the oxidization of hydrogen peroxide. (1 mark)  State the expected observation and write a chemical equation for the reaction involved. (2 marks) 8.(b)(i) H2O2O2 H2O2O2 +2H+ + 2e- 2OH- + H2O2 O2 +2H+ + 2e- + 2OH- 2OH-(aq) +H2O2(aq) O2(g) +2H2O (l) + 2e- [1] 8.(b)(ii) colourless gas bubbles can be seen. / solution turns form yellow to green [1] 2Fe3+ +2OH- +H2O2 2Fe2+ +O2 +2H2O [1] X H2O2 dissolves

  31. 9. (a) Describe the structure of buckminsterfullerene. (2 marks) P.32 9.(a) It consists of 60 carbon atoms [0.5] bonded with covalent bonds. [0.5] in a nearly spherical configuration [0.5] with each 5-membered ring is surrounded by five 6-membered rings. [0.5] X open-caged X wrong spellings X Carbon molecules.

  32. (b) Compare the differences of two physical properties between graphite and buckminsterfullerene. (2 marks) 9.(b) Graphite has a higher melting point than C60. [1]Graphite is insoluble in aqueous or non-aqueous solvent, but C60 is soluble in organic solvent. [1] No need explanation!

  33. c) State the differences of the structures and bondingsbetween graphite and buckminsterfullerene, (2 marks) 9.(c) Graphite has a giant covalent structure with strong covalent bonds between C atoms [1], with van der Waal’s forces between layers. and C60 has a simple molecular structure with weak van der Waal’s forces between C6o molecules. [1] P.34 2.Compare the difference in properties between diamond , graphite and C60. Explain differences in terms of their structure and bonding.

  34. 10. Four iron-made objects are placed separately in gel with rust indicator solution containing potassium hexacyanoferrate(III), and allowed to stand in air for some time. Write down the observation and giving the relevant explanation for each of the cases on the answer book.

  35. Prevent Fe to form Fe2+ X 1. No blue colour X Zn rust X Fe does not rust X Colourless gas bubbles because Zn reacts with the hot gel (Mg can react with the hot water in the gel not Zn )

  36. P.249, 304

  37. 11. Lead (Pb) is an element in Group IV of the Periodic Table. An oxide of lead, X, contains 90.6% of lead by mass. Calculate the empirical formula of X. (3 marks) Let the mass of lead oxide be 100g Pb O Mass in gram 90.6 9.4 No. of moles [1] 0.4373 0.5875 o3 4 [1] Empirical formula of X is Pb3O4 [1] Divided both answers by the smaller answer Muitlply by 2/3/4/…. Until you can get a whole number X 1.3 cannot round up to 1 X multiply by 10

  38. 12. An astronaut exhales 1.1 kg of carbon dioxide per day in a spaceship. This carbon dioxide can be absorbed by solid lithium hydroxide. (a) Write a balanced full equation for the reaction between lithium hydroxide and carbon dioxide. (1 mark) (b) Calculate the mass of lithium hydroxide required per day for a crew of 3 astronauts. (3 marks) (c) An alternative to lithium hydroxide for the removal of carbon dioxide in the spaceship is sodiumperoxide according to the following equation: 2Na2O2(s) + 2CO2(g)  2Na2CO3(s) + O2 (g) Suggest ONE advantage of using sodium peroxide rather than lithium hydroxide.(1 mark) LiOH(s) + CO2 (g) base+ acid  salt + water 2LiOH (s) + CO2(g) Li2CO3(s) + H2O (l) [1] Or 2LiOH + H2CO3 Li2CO3 + 2 H2O b) total mass of CO2 produced by 3 astronauts = 3 x 1.1 x 1000g 3300g [1] No. of moles of CO2 produced = 3300/(12+32) = 75 [1] no. of moles of LiOH required = 2 x 75 x (6.9+ 16+1) = 3585 g [1] (c) Advantage: It produces oxygen for the astronauts to breathe. [1]

  39. 1. Which of the following combinations is INCORRECT? • Chemical Method of storage • A. Calcium Under water • B. Potassium Under paraffin oil • C. Ethanol (alcohol) In a cool place • D. Potassium permanganate solution In a brown bottle • ---Ca reacts with water • --- Potassium permanganate solution, AgNO3 and HNO3 can be decompose under sunlight

  40. 2. Calcium carbonate can be obtained from quicklime through two processes as shown below. • Process 1 Process 2 • Quicklime  Limewater  Calcium carbonate • CaO Ca(OH)2 CaCO3 • Which of the following combinations is correct? • Process 1 Process 2 • A. Adding water Adding Na2CO3(aq) • B. Adding Na2CO3(aq) Adding water • C. Adding water Heating • Heating Adding water • CaO + H2OCa(OH)2 • Ca(OH)2 (aq) + Na2CO3(aq)  • CaCO3(s)+NaOH (aq) • A

  41. 3. A student has performed the following tests on solid sample Y: Y is A. Calcium carbonate. B. Calcium chloride. C. Sodium chloride. • Potassium sulphate. • C

  42. 4. X is an element. It can form a cation X2+which has an electronic arrangement 2, 8, 8. Which of the following statements concerning X are correct? • (1) X is a strong oxidizing agent. • (2) X is in Period 4 of the Period Table. • (3) X burns in oxygen with a brick red flame. • A. (1) and (2) only • B. (2) and (3) only • C. (1) and (3) only • (1),(2) and (3) • X--- 2,8,8,2 • B

  43. ***5. When a neutron is added to the nucleus of an atom, A. the atomic number of the atom increases. B. the attraction between the nucleus and the electrons increases. C. the new atom is an isotope of the original atom. the atomic mass does not change. A ---Proton increases B. --- neutron carries no charge D --- mass increased by 1 C --- isotope– atoms of same elements with same no. of P and diff no. of n.

  44. ***6. How many moles of C2H6 contain y hydrogen atoms? (L represents the Avogadro’s constant.) A. y/L B. L/y C. y/6L 6y/L I mole C2H6 contains 6L hydrogen atoms X moles C2H6 contains yhydrogen atoms X/1 = y/6L C

  45. 7. What is the number of moles of Fe3+ ions in 0.1dm3 of 0.5 M Fe2(SO4)3 solution? A. 0.1 × 0.5 B. 2 × 0.1 × 0.5 C. 0.1 × 0.5 × 6.02 × 1023 D. 2 × 0.1 × 0.5 × 6.02 × 1023 No. of moles of Fe2(SO4)3 = 0.1 x 0.5 No of moles of Fe3+ = 0.1 x 0.5 x 2 B

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