multiple choice questions answer all questions on the ... chemical principles s1 2011 final...

PEC144 Chemical Principles S1 2011 Final Examination

of 32 Multiple Choice Questions

60 Questions worth 1.5 marks each (90 marks)

Answer all questions on the computer-readable answer sheet provided

1. Which of the following statements are correct?

I. The frequency (ν) and wavelength (λ) of electromagnetic radiation are inversely related

II. Electromagnetic radiation has properties of both waves and particles III. The energy (E) of electromagnetic radiation is directly related to frequency (ν) IV. Electrons have properties of both waves and particles

A. None of the statements are correct B. I and II only C. II, III and IV only D. II and IV only E. I, II, III and IV

2. Which one of the following statements is correct?

A. Both the energy and location of an electron in an atom can be described precisely B. Neither the energy nor location of an electron in an atom can be described precisely C. The energy of an electron in an atom can be described precisely, but its location can

only be described in terms of probability D. The location of an electron in an atom can be described precisely, but its energy can

only be described in terms of probability E. None of the above statements is correct

3. Which one of the following statements is incorrect?

A. A maximum of 6 electrons can occupy p orbitals B. A 2s orbital is higher in energy than a 1s orbital C. Orbitals that have the same energy are termed degenerate D. The d orbitals within an electron shell have different energy E. Increasing value of principle quantum number represents increasing orbital size

4. Which one of the following statements about an electron shell with n = 3 is correct?

A. There are 9 subshells within this shell B. There are 9 orbitals within this shell C. A maximum of 8 electrons can occupy this shell D. The shell only has s and p orbitals E. None of the above statements are correct

Question 5 follows


of 32 5. Which one of the following is the correct electron configuration for a ground-state nitrogen atom?

A.

B.

C.

D. E. None of the above

6. Which one of the following pairs do not have the same electron configuration?

A. Sr2+ and Br‾ B. S2– and Ar C. F‾ and Na+ D. He and H‾ E. Ne and Cl‾

7. Which one of the following electron configurations depicts an excited carbon atom?

A. [He]2s22p

2 B. 1s

22s12p

23s1

C. 1s22s

22p3

D. 1s22s

22p2

E. 1s22s

12p33s

1 8. Which one of the following represents the most stable electron configuration for Mn2+?

A. [Ar]4s03d

5 B. [Ar]4s

13d4

C. [Ar]4s23d

3 D. [Ar]4s

33d2

E. None of the above

Question 9 follows


of 32 9. Which one of the following compounds obeys the ‘octet rule’?

A. NO2 B. BF3 C. XeF2 D. SF6 E. H2S

10. How many electron domains surround the central atom in the XeF2?

A. 2 B. 3 C. 4 D. 5 E. 6

11. Which one of the following gives the correct electron domain geometry and molecular geometry for the species I3¯?

Electron domain geometry Molecular geometry

A. Linear Linear B. Trigonal planar Bent C. Tetrahedral Bent D. Trigonal bipyramidal Linear E. Trigonal bipyramidal Bent

12. Which one of the following gives the correct electron domain geometry and molecular geometry for the species ICl4¯?

Electron domain geometry Molecular geometry

A. Tetrahedral Tetrahedral B. Trigonal bipyramidal T-shaped C. Octahedral Square planar D. Octahedral Square pyramidal E. Trigonal bipyramidal Seesaw

13. What type of electron domain geometry is associated with the carbon atom in HCN?

A. Linear B. Trigonal planar C. Tetrahedral D. Trigonal bipyramidal E. Octahedral

Question 14 follows


of 32 14. In which one of the following compounds is the central atom not sp

3 hybridised?

A. SF4 B. H2S C. SiH4 D. PBr3 E. CCl4

15. What is the hybridisation of the central atom in AlCl3?

A. sp B. sp

2 C. sp

3 D. sp

3d

E. sp3d

2 16. What type of hybridisation is associated with trigonal bipyramidal electron domain geometry?

A. sp B. sp

2 C. sp

3 D. sp

3d

E. sp3d

2 17. Which one of the following is the best estimate of the H–O–H bond angles in the water (H2O) molecule?

A. 180o B. > 180o C. < 109.5o D. 109.5o E. > 109.5o but < 180o

18. Which one of the following statements about solutions is incorrect?

A. A solution can be heterogeneous B. Solutions may be solid, liquid or gas C. The solvent is the dissolving medium D. The solute is the substance dissolved in the solvent E. Each substance in a solution is called a component

Question 19 follows


of 32 19. Which one of the following best describes the nature of the solute-solvent interactions in a solution of bromine (Br2) in water (H2O)?

A. London dispersion forces B. Ion-dipole attraction C. Dipole-dipole attraction D. Dipole-induced dipole attraction E. Hydrogen bonding

20. Which one of the following statements is incorrect?

A. The extent of attractive forces between the solute and solvent particles influences solubility

B. A saturated solution is one in which the maximum amount of solute has dissolved C. The solubility of most solid substances in solutions increases with increasing

temperature D. The solubility of gaseous substances in solution increases with increasing temperature E. The solubility of gases increases with increasing partial pressure of the gas above the

solution 21. Which one of the following substances would be the most soluble in hexane (C6H14)?

A. NH3 B. C10H22 C. H2O D. NaCl E. CH3CH2OH

22. Which of the following statements concerning the dissolution of an ionic solid in water is/are correct?

I. The extent of dissolution of an ionic solid is governed by the strength of the attractive forces between the ions and water molecules and the lattice energy of the ionic solid

II. Dissolution of an ionic solid always leads to a more ordered system due to the formation of a hydration sphere around the ions

III. Hydration of ions (the surrounding of ions by water molecules) releases energy

A. I only B. I and II only C. II and III only D. I and III only E. I, II and III

Question 23 follows


of 32 23. Given the molar conductivities of the following salts, calculate the theoretical molar conductivity of CsF under the same conditions.

CsNO3 Λ = 14.87 mS m2 mol–1 HNO3 Λ = 42.11 mS m2 mol–1 HF Λ = 40.50 mS m2 mol–1

A. 25.63 mS m2 mol–1 B. 13.26 mS m2 mol–1 C. 16.48 mS m2 mol–1 D. 97.48 mS m2 mol–1 E. The concentrations of the solutions need to be known to answer this question

24. Assuming ideal behaviour, which option below shows the correct order of increasing vapour pressure for the following aqueous solutions? Assume that the solute does not contribute to the vapour pressure above the solution.

I. Pure water II. 10 g of ethanol in 1 kg of water III. 10 g of propanol in 1 kg of water IV. 10 g of butanol in 1 kg of water

A. I < III < II < IV B. I < IV < III < II C. IV < III < II < I D. II < III < IV < I E. Insufficient information to answer this question.

Questions 25 and 26 concern a sealed vessel containing N2O4(g) and NO2(g) in equilibrium according to the equation below. The reaction, as shown, is endothermic.

N2O4 (g) 2 NO2 (g) 25. How does the amount of NO2 (g) present change due to the following changes to the system?

I. Adding N2O4 II. Increasing the volume of the container III. Lowering the temperature IV. Adding a catalyst to the system

A. I: increase, II: increase, III: decrease, IV: no change B. I: increase, II: increase, III: increase, IV: increase C. I: increase, II: increase, III: increase, IV: no change D. I: increase, II: increase, III: decrease, IV: increase E. I: increase, II: decrease, III: increase, IV: no change

Question 26 follows


of 32 26. Which of the changes to the system will result in an altered value for the equilibrium constant, K, of the system?

A. I B. II C. III D. IV E. None of the changes will result in a change in the value of K

27. Which one of the following statements best describes the approximate equivalence point of a titration between acetic acid (in a conical flask) and sodium hydroxide (in a burette) and why it occurs?

A. The equivalence point of the titration will be alkaline because at the equivalence point there is a slight excess of the strong base, sodium hydroxide, present

B. The equivalence point of the titration will be alkaline because at the equivalence point the acetate ions react with water to produce a small amount of hydroxide ion in solution

C. The equivalence point of the titration will be neutral D. The equivalence point of the titration will be acidic because at the equivalence point

there is a slight excess of the weak acid, acetic acid, present E. The Ka of acetic acid needs to be known to predict the equivalence point pH of this

titration 28. The Kw of water has the following values:

1.14 x 10–15 at 0ºC 1.00 x 10–14 at 25ºC 5.47 x 10–14 at 50ºC

A neutral aqueous solution would be best described as:

A. pH = 7.00 for all three temperatures B. pH = 14.9 at 0ºC, pH = 14.0 at 25ºC and pH = 13.3 at 50ºC C. [H+] = 1.00 x 10–7 for all three temperatures D. [H+] = [OH‾] for all three temperatures E. Additional information is required to answer the question

29. Which of the following sets of fundamental units represent the joule (J)?

A. kg m–2 s–2 B. kg m s–2 C. kg m–1 s–2 D. kg m2 s–2 E. none of the above

Question 30 follows


of 32 30. If the same amount of heat is added to 50.0 g samples of each of the metals below, which metal will experience the largest temperature change?

Metal Specific Heat Capacity (J g–1 K

–1)

Al 0.897 Au 0.129 Cu 0.385 Fe 0.449 K 0.753

A. Al B. Au C. Cu D. Fe E. K

31. Wind imparts 200 J of work to a wind turbine system while the turbine delivers 150 J of electrical energy to an external load. Which of the following statements is true?

A. the internal energy change of the system is +350 J B. the internal energy change of the system is –350 J C. the internal energy change of the system is +50 J D. the internal energy change of the system is –50 J E. the temperature of the system must decrease

32. Which of these substances has the lowest entropy (J mol–1 K–1)?

A. water vapour B. liquid water C. an aqueous solution of NaCl D. pure solid glucose (C6H12O6) E. ice

33. The ‘temperature’ of a material:

A. is a property associated with molecular movement B. is not a state function C. depends on the amount of material D. all of the above E. none of the above

Question 34 follows


of 32

34. Which of the following statements best describes the entropy change (∆S) during the reaction shown below?

2NH3(g) → N2(g) + 3H2(g)

A. ∆S < 0

B. ∆S = 0

C. ∆S > 0

D. sign of ∆S depends on the temperature at which the change takes place E. there is no entropy change in this system

35. The enthalpy change during a reaction is positive. Which of the following statements must be false?

A. The reaction is endothermic B. The reaction is exothermic C. The reaction is product-favoured D. The reaction is reactant-favoured E. The reaction is rapid

Questions 36 and 37 concern a particular reaction where:

∆H = −32 kJ

∆S = −98 J K−1 36. Assuming that enthalpy and entropy do not vary with temperature, at what temperature will the reaction be at equilibrium?

A. −330 K B. 330 K C. 330 °C D. 0.33 K E. 0.33 °C

37. If the reaction mixture is held at a temperature of 0°C, will the reaction occur spontaneously or not?

A. The reaction is spontaneous at all temperatures

B. ∆G = −32 kJ, reaction is spontaneous

C. ∆G = −32 kJ, reaction is non spontaneous

D. ∆G = −5.2 kJ, reaction is spontaneous

E. ∆G = −5.2 kJ, reaction is non spontaneous

Question 38 follows


of 32 38. The value of the equilibrium constant for a reaction is less than 1. Which of the following statements is true?

A. ∆G° > 0, the reaction is reactant favoured

B. ∆G > 0, the reaction is reactant favoured

C. ∆G° < 0, the reaction is product favoured

D. ∆G < 0, the reaction is product favoured E. The temperature of the system must be known to answer this question

39. Which of the following statements is true?

A. a coffee cup calorimeter can be modelled as an open system B. a biological cell can be modelled as an open system C. an isolated system can exchange heat with the surroundings D. a closed system cannot exchange heat with its surroundings E. none of the above statements is true

40. A reaction is occurring spontaneously. Which of the following statements cannot be true?

A. the reaction is exothermic B. the reaction is endothermic C. the entropy is increasing D. the Gibbs energy change is negative E. the Gibbs energy change is positive

41. The standard Gibbs energy change for a reaction is related to the equilibrium constant by

∆Go = –RT ln K , where R is the gas constant, 8.3145 J K–1 mol–1. For a particular reaction ∆Go is –1725 J mol–1. The equilibrium constant for this reaction is therefore

A. –2 B. +2 C. –2 kJ D. +2 kJ E. 0.694

42. A substance increases in temperature as a given quantity of heat is transferred to it. Which of the following statements is true?

A. the magnitude of the temperature change is independent of the composition of the substance under consideration

B. the magnitude of the temperature change is inversely proportional to the quantity of heat transferred

C. the magnitude of the temperature change is proportional to the quantity of heat transferred

D. the magnitude of the temperature change is proportional to the mass of substance under consideration

E. all of the above are true Question 43 follows


of 32 43. The standard enthalpy values for reactions 1 and 2 shown below are provided.

1. C(s) + O2(g) → CO2(g) ∆1Hº = –394 kJ 2. CO(g) + 0.5 O2(g) → CO2(g) ∆2Hº = –283 kJ 3. C(s) + 0.5 O2(g) → CO(g) ∆3Hº = ? kJ

The standard enthalpy change for reaction 3 must be:

A. –111 kJ B. –222 kJ C. +111 kJ D. +222 kJ E. –677 kJ

44. Enthalpy is a very useful thermodynamic quantity because it relates to measurements of heat made in a system which is:

A. isolated B. at constant pressure C. constant volume D. at constant temperature E. containing a spontaneous reaction

45. The standard formation reaction of 2,2,2-trichloroethanol (Cl3CCH2OH) a compound with melting and boiling points of 292 and 424 K respectively, is best represented as:

A. 4 C (s, graphite) + 3 Cl2 (g) + 3 H2 (g) + O2 (g) → 2 Cl3CCH2OH (l) B. 4 C (s, graphite) + 3 Cl2 (g) + 3 H2 (g) + O2 (g) → 2 Cl3CCH2OH (s) C. 2 C (s, graphite) + 1.5 Cl2 (g) + 1.5 H2 (g) + 0.5 O2 (g) → Cl3CCH2OH (l) D. 2 C (s, graphite) + 1.5 Cl2 (g) + 1.5 H2 (g) + 0.5 O2 (g) → Cl3CCH2OH (s) E. 2 C (s, graphite) + 3 HCl (g) + 0.5 O2 (g) → Cl3CCH2OH (l)

46. When ammonium nitrate dissolves in water at constant pressure, the temperature of the solution falls. Which of the following statements must be correct?

A. The process is endothermic B. The process is product-favoured

C. ∆S > 0

D. ∆G > 0

E. ∆H < 0

Question 47 follows


of 32 47. The term ‘reaction kinetics’ is best defined as:

A. the energy flows in chemical reactions B. chemical processes at a macroscopic level C. the sequence of events that occur at the molecular level when a chemical reaction

takes place D. thermodynamic prediction of which chemical reactions are possible E. studies of the rates at which processes occur and the factors affecting the rates

48. The term ‘reaction mechanism’ applies to:

A. the energy flows in chemical reactions B. chemical processes at a macroscopic level C. the sequence of events that occur at the molecular level when a chemical reaction

takes place D. thermodynamic prediction of which chemical reactions are possible E. studies of the rates at which processes occur and the factors affecting the rate

49. Hydrogen peroxide decomposes according to the following stoichiometry.

2H2O2 (aq) → 2H2O (aq) + O2 (g) Which of the following statements is true?

A. d[H2O2]/dt = d[H2O]/dt B. d[H2O2]/dt = d[O2]/dt C. d[H2O2]/dt = –d[O2]/dt D. d[H2O2]/dt = –d[H2O]/dt E. none of the above statements are true

50. The concentration of a substance (X) in solution changes from 8.73 mM to 5.54 mM over 40 minutes. The average rate of change in concentration of X is then:

A. –4.79 mM h–1 B. –3.19 mM h–1 C. –6.0×10–4 mol L–1 s–1 D. –2.13 mol L–1 h–1 E. +0.0798 mol L–1 min–1

51. The first order reaction of N2O4 to form two mole of NO2 has a rate constant k = 0.023 min–1. How long will it take the initial concentration of N2O4 to decrease to 10 % of the original value?

A. 600 s B. 43.5 s C. 43.5 min D. 435 min E. 100 min

Question 52 follows


of 32 52. During a study of the hydrolysis of 2-chloro-2-methyl propane {(CH3)3CCl}, the reaction stoichiometry and the rate equation are found to be:

(CH3)3CCl + H2O → (CH3)3COH + H+ + Cl‾ rate = k [(CH3)3CCl]

The reaction rate when [(CH3)3CCl] = 0.0144 M was found to be 2.074×10–4 M s–1. The correct value and units of the rate constant (k) are:

A. 2.987×10–6 s–1 B. 0.0144 s–1 C. 69.43 s–1 D. 69.43 mol–1 L s–1 E. 0.0144 mol–1 L s–1

Questions 53 and 54 are about the structure of paracetamol shown below.

N

O

CH3

H

OH

53. The amide group in paracetamol may be classified as which one of the following?

A. Primary (1o) B. Secondary (2o) C. Tertiary (3o) D. Quaternary (4o) E. None of the above

54. The carbon atom labelled with an asterisk (*) may be classified as which one of the following?

A. Primary (1o) B. Secondary (2o) C. Tertiary (3o) D. Quaternary (4o) E. None of the above

Question 55 follows

*


of 32 55. Which one of the following statements about the alkenes shown below is correct?

NH2

N CH2CH3

CH2CH2CH3

H

CH3

CH3

H CH2OH

OH

O

Alkene I Alkene II

A. Both alkenes may be classified as Z B. Both alkenes may be classified as E C. Alkene (I) is E and alkene (II) is Z D. Alkene (I) is Z and alkene (II) is E E. None of the above statements are correct

56. The equation shown below represents the synthesis of an amide from an amine and an acid chloride. This reaction may best be classified as which one of the alternatives given?

NH2

+Cl

O

CH3N CH3

O

H

+ HCl

A. Substitution B. Addition C. Saponification D. Reduction E. Condensation

57. The compounds shown below are all weak acids. Which one of the options shows the correct order of acidity from strongest to weakest?

I. II. III. IV. V.

OH

O

OH

O

Cl

OH

OH

O

Cl

OH

A. I > II > III > IV >V B. V >IV >II> I > III C. V > IV >III >II >I D. IV > II >I >V >III E. III > V >I > II > IV

Question 58 follows


of 32 58. Which Newman projection/s represents the lowest energy eclipsed conformation of butane (CH3CH2CH2CH3)? I. CH3

CH3

H

H

H

H

II. H3CH

HH

CH3H

III. CH3

H

H

H

CH3

H

IV. H3CCH3

HH

HH

V. CH3

H

H3C

H

H

H

VI. H3CH

HH3C

HH

A. I B. II and VI C. III and V D. IV E. The lowest energy eclipsed conformation is not shown

Questions 59 and 60 are about the reaction of 2-methylbut-1-ene with HBr. In this reaction there are two possible intermediates (A and B) shown with the structure of the reactant below.

2-Methylbut-1-ene Intermediate A Intermediate B

C C

H

H CH3

CH2CH3

C C

H

H CH3

H

CH2CH3

C C

H

H

H

CH3

CH2CH3

59. Intermediate A may be classified as which one of the following?

A. Primary (1º) radical B. Tertiary (3º) radical C. Primary (1º) carbocation D. Tertiary (3º) carbocation E. None of the above

Question 60 follows


of 32 60. Which one of the following statements about Intermediate B is correct?

A. Intermediate B is less stable than Intermediate A B. Intermediate B is more stable that Intermediate A C. Intermediate B has the same stability as Intermediate A D. Intermediate B is more likely to form than Intermediate A E. None of the above statements about Intermediate B are correct

End of Multiple Choice Questions

Short Answer Questions (61 – 80) Follow


of 32 Short Answer Questions (90 marks)

Answer all questions in the spaces provided

Question 61 (4 marks)

a) Draw a Lewis structure for the species ClF4

+ in the space provided on the right. Ensure that you include all lone pairs. (2 marks)

b) Draw two resonance structures for formate ion (HCO2¯). (2 marks)


Explain the nature of the solvent-solute interactions for a solution of sodium chloride (NaCl) in water. Use a simple illustration to explain your answer. Explanation (1 mark) Illustration (1 mark)

Question 63 follows


of 32 Question 63 (6 marks)

a) The structure of octocrylene, which is used in some sunscreens, is shown below. Explain why octocrylene is able to be used as a sunscreen. Clearly highlight the part of the molecule responsible for sunscreen action.

Explanation of sunscreen activity (1 mark) Highlight the part of the molecule responsible for sunscreen action (1 mark)

N

O

O

b) A 752 mg sample of sunscreen containing octocrylene was extracted with ethanol and the final volume of the solution was 25.0 mL. Using a 1 cm path length sample cell, the absorbance of the solution was determined to be 3.62 at 304 nm. The molar absorptivity of octocrylene in ethanol at this wavelength is 350 L mol–1 cm–1 and the molar mass of this compound is 361 g mol–1. Calculate the mass percentage of octocrylene in the sunscreen.

(4 marks) Question 64 follows



An aqueous solution has been prepared that is known to be 27.8 % w/w glucose (C6H12O6). a) What mass of glucose is present in 100. g of the solution? (1 mark) b) What mass of water is present in 100. g of the solution? (1 mark) c) How many moles of glucose are present in 100. g of the solution? (1 mark) d) What is the molality of glucose in the solution? (1 mark) Question 65 (4 marks)

Consider a 1.50 mol kg–1 solution of carbonic acid (H2CO3) in water. a) What is the theoretical molality of ions in this solution? (1 mark)

Question 65 continues


of 32 Question 65 continued

b) If the solution boils at 100.95 ºC, calculate the actual concentration of ions in the solution. Water has a boiling point elevation constant of 0.51 ºC kg mol–1 and boils at 100.00 ºC. (2 marks) c) Based on your answers to parts a) and b), which one of the following best describes how carbonic acid mainly exists in this solution? Clearly indicate your choice with a tick. (1 mark) H2CO3

HCO3‾ + H+ CO32– + 2 H+

Question 66 (5 marks) Epinephrine is a hormone that regulates stress responses. 0.804 g of epinephrine was dissolved in water and made up to the mark in a 500. mL volumetric flask. The resulting osmotic pressure of the solution was observed to be 21.7 kPa at 25 ºC. What is the molar mass of epinephrine? {R = 8.314 L kPa K–1 mol–1}

Question 67 follows



Calcium chromate (CaCrO4) has relatively low solubility in water. At 25 ºC the Ksp of calcium chromate is 7.1 x 10–4. a) Write an equation for the reaction of calcium chromate dissolving into water and forming its constituent ions (1 mark) b) Write the equilibrium expression (Ksp) for calcium chromate, based on the above equation. (1 mark) 100. mL each of 0.02 mol L–1 sodium chromate and 0.01 mol L–1 calcium nitrate are mixed. c) What is the concentration, in mol L–1, of chromate ions in the mixed solution? (1 mark) d) What is the concentration, in mol L–1, of calcium ions in the mixed solution? (1 mark) e) What is the reaction quotient for calcium chromate in this system? (1 mark)




f) Will a precipitate form? Explain your answer. (2 marks) Question 68 (7 marks)

a) Write a balanced chemical equation for the acid dissociation reaction of hypochlorous acid (HOCl) in water. (1 mark) b) Write the Ka expression for HOCl based on the above equation. (1 mark) c) The pH of a solution of hypochlorous acid (HOCl) in water was found to be 3.9. What is the concentration of protons in this solution? (1 mark) d) What is the concentration of the hypochlorite ion (OCl‾) in this solution? (1 mark)




e) The total concentration of hypochlorous acid used to make the solution was 0.5 mol L–1. What is the value of the acid dissociation constant for hypochlorous acid? (2 marks) f) What is the percent dissociation of hypochlorous acid in this solution? (1 mark) Question 69 (2 marks)

An aqueous solution can prepared of the complex ion between silver ions and ammonia (Ag(NH3)2

+) by the addition of 4 mL of 4 M ammonia to 1 mL of 0.1 M AgNO3. As the ammonia solution is added, a white precipitate is observed to form and then dissolve upon continued addition of the ammonia solution. Explain the observation of the transitory precipitate described above (appearance and disappearance), using equations where appropriate.

Question 70 follows



Hydrothermal vents in the ocean offer a unique environment for growth in which only specialist organisms, such as the Pompeii worm, may grow due to the extreme temperature, pressure and pH conditions as well as the range of toxic chemicals found. To simulate the conditions near an ocean vent, an aquatic chemist wishes to make a solution in which the pH will be held constant at 3.50. The following materials are available. I. 2.00 L of a starting solution, 1.25 mol L–1 chloroacetic acid (ClCH2COOH, pKa = 2.85)

and solid sodium chloroacetate (ClCH2COONa, molar mass 116.48 g mol–1) II. 2.00 L of a starting solution, 1.25 mol L–1 nitrous acid (HNO2, pKa = 3.15) and solid

sodium nitrite (NaNO2, molar mass 69.00 g mol–1) III. 2.00 L of a starting solution, 1.25 mol L–1 acetic acid (CH3COOH, pKa = 4.74) and

solid sodium acetate (CH3COONa, molar mass 82.04 g mol–1) a) Which buffer system would best suit the needs of the scientists studying hydrothermal vents? Clearly indicate your choice with a tick. (1 mark) Chloroacetic acid/ sodium chloroacetate

Nitrous acid/ sodium nitrite

Acetic acid/ sodium acetate

b) What concentration of the conjugate base (ie depending on your answer to part a: either sodium chloroacetate, sodium nitrite or sodium acetate) is required to produce an appropriate buffer using the starting solution given? (4 marks)




c) What mass (grams) of the solid (ie depending on your answer to part a: either sodium chloroacetate, sodium nitrite or sodium acetate), is required to produce an appropriate buffer using the starting solution given? (2 marks)


A sample of pure KNO3 (2.443 g, 101 g mol–1) is dissolved in 50.0 g of water contained in an insulated calorimeter at 1 atmosphere pressure. The temperature fell from 24.3 to 18.4 ºC as the reaction below occurred.

KNO3(s) → K+ (aq) + NO3‾ (aq) Given that the heat capacity of water is 4.182 J K–1 g–1, calculate a value for the change in enthalpy (∆H) during for this reaction as written and give its units.

Question 72 follows



The following data were measured for the reaction of nitric oxide with hydrogen, which is shown in the equation below.

2 NO (g) + 2 H2 (g) → N2 (g) + 2 H2O (g)

Experiment

number

(H2) (mol L–1) (NO) (mol L

–1) Initial rate (v)

(mol L–1 s–1)

1 0.1 0.1 1.23 × 10–3 2 0.1 0.2 2.46 × 10–3

3 0.2 0.1 4.92 × 10–3 Conditions were chosen such that the general form of the rate equation was:

v = k (NO)m (H2)n

where m and n are integers. From this information, deduce the values of m, n, and the rate constant k.

Numerical value of m

Numerical value of n

Numerical value of k

Units of k


Draw curved arrows to show the movement of electrons for the interconversion between resonance structures for the amide shown below.

N

O

H3C

H

CH3N

O

H3C

H

CH3

Question 74 follows



A chemist has carried out a reaction to convert butanoic acid to phenyl butanoate; the structures of these compounds are shown below. The product from the reaction was a mixture containing about 10% of the unreacted butanoic acid and 90% of the desired ester. Outline an extraction procedure that the chemist could carry out to remove the butanoic acid and isolate the phenyl butanoate. There is no need to isolate the butanoic acid.

OH

O

O

O

Butanoic acid Phenyl butanoate

Question 75 follows



Samples of oct-1-yne and octan-2-ol have been mixed up in the lab. In order to determine which compound is which you label them A and B and obtain the IR spectrum of each sample. a) Examine the spectra shown below and determine which is attributable to each compound. Write the name of the compound in the box to the right of each spectrum. (2 marks) b) Ignoring the fingerprint region (400 cm–1 – 1500 cm–1), clearly label the characteristic absorption bands for O–H, sp3 C–H, C≡C and ≡C–H groups in the spectrum/spectra in which they appear. (4 marks)

Question 76 follows

Wave numbers cm-1

4000 400

Spectrum A

Spectrum B



a) The names, melting points and structures of two fatty acids are shown below. Both compounds consist of a carboxylic acid group and a hydrocarbon chain of 18 carbon atoms. Explain the difference in melting point between the two compounds.

Stearic acid

Melting point = 70 oC OH

O

Oleic acid

Melting point = 14 oC

OH

O

(3 marks) b) Saponification of triglycerides gives glycerol and fatty acid salts as shown in the equation below. The groups R1, R2 and R3 represent hydrocarbon chains that may be the same or different.

O

O

O

R1

O

O

R2

O

R3

OH

OH

OH +

O

O

R1Na

O

O

R2Na

O

O

R3Na

NaOH

H2O

Saponification is actually a hydrolysis reaction. Explain what a hydrolysis reaction is and the role of sodium hydroxide in this process.

(2 marks) Question 77 follows



a) Use the Cahn-Ingold-Prelog sequence rules to rank the following set of substituents in order of priority from 1 (highest) to 4 (lowest). (1 mark) Substituent

–CH2NH2 –CH=CH2 –CH2OH –CH2CH3

Priority

b) The over-the-counter drug Ibuprofen is a 1:1 mixture of R and S isomers of the compound 2-(4-isobutylphenyl)propanoic acid. The two compounds have identical physical properties, but only the S isomer has drug activity. Explain the structural difference between these isomers that accounts for these observations. (2 marks) c) Draw the structure for the following compound using the convention required to show the stereochemistry. (1 mark)

Compound name Structure

trans-1,4-dimethylcyclohexane

d) The structure of pyrethrum, a naturally occurring insecticide, is shown below. Examine the structure and clearly circle the stereogenic centre/s. (1 mark)

Question 78 follows

O

O

O



Halogenation of alkanes in the presence of light is an example of an organic reaction that occurs via free radical intermediates. One example of this is the reaction between methane and chlorine shown in the equations below. Free radical reactions occur in a series of steps called Initiation, Propagation and Termination. Write equations to show an example of each of these steps in the reaction of methane with chlorine in the presence of light.

Initiation reaction

(1 mark) Propagation reaction

(1 mark) Termination reaction

(1 mark) Question 79 (3 marks)

Complete the following table by drawing the structure of each compound.

Name Structure

1-chloro-2-methylbenzene

(1 mark)

1-ethoxypropane

(1 mark)

N-ethylbutan-1-amine

(1 mark) Question 80 follows



The preparation of ethoxybenzene from the reaction between sodium phenoxide and bromoethane is shown in the equation below. Like most organic reactions, this can be described as an interaction between an electron rich species (nucleophile) and an electron deficient species (electrophile). a) Examine the equation and clearly label each reactant as the nucleophile or electrophile as appropriate. (2 marks)

O Na

+ CH3CH2Br

OCH2CH3 + NaBr

b) Write an equation to show how sodium phenoxide could be prepared from phenol (hydroxybenzene).

(2 marks)

End of Examination

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