CAPE WINELANDS EDUCATION DISTRICT

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1 Physical Sciences/P2 1 NSC CWED September 2014 CAPE WINELANDS EDUCATION DISTRICT PHYSICAL SCIENCES P2 CHEMISTRY SEPTEMBER 2014 MARKS: 150 TIME: 3 hours This exam paper consists of 14 pages and four data sheets.

2 INSTRUCTIONS AND INFORMATION Write your NAME on the ANSWER FOLIOS. Answer ALL the questions on the ANSWER FOLIOS. You may use a non-programmable calculator. You may use appropriate mathematical instruments. Start each main question on a new page. Number the answers correctly according to the numbering system used in this question paper. YOU ARE ADVISED TO USE THE ATTACHED DATA SHEETS. Give brief motivations, discussions, et cetera, where required. Round off calculations to two decimal places. QUESTION 1: MULTIPLE CHOICE Four options are provided as possible answers to the following questions. Each question has only ONE correct answer. Write only the letter (A D) next to the question number ( ) on one page of your ANSWER FOLIO S. 1.1 The correct IUPAC name of the following compound is: CH 3 CH 3 CH 2 CH CH CH 3 Cl A 3-chloro-4-methylpentane B 3-chloro-2-methylpentane C 2-methyl-3-chloropentane D 4-methyl-3-chloropentane. (2) 1.2 Which one of the following statements is INCORRECT? A Sunflower oil undergoes a substitution reaction to form margarine B Alkynes are more reactive than alkenes C Aldehydes and ketones contain a carbonyl group D Propyl ethanoate can be made from propanoic acid and ethanol. (2) 2

3 1.3 Consider graph A and B below. Graph A shows the distribution of molecular energies. X represents the minimum kinetic energy required for a reaction. Graph A number of molecules kinetic energy X Graph B shows the potential energy curve for the same reaction is represented below. Which of the following will be the correct value for X shown in graph A? Ep B C A D A B C D 10 kj 103 kj 93 kj 35 kj course of reaction (2) 3

4 1.4 The reaction represented by the balanced equation below reaches equilibrium in a closed container. H 2 (g) + I 2 (g) 2HI(g) H < 0 How will the equilibrium be affected if, first the volume of the container is decreased and then the temperature is increased? A At first no effect and then the reverse reaction is favoured. B The reverse reaction is favoured by both changes. C At first no effect and then the forward reaction is favoured D A first the reverse reaction is favoured and then the forward reaction is favoured. (2) 1.5 Consider the reversible reaction: N 2 (g) + 3 H 2 (g) 2 NH 3 (g) H < 0. The graph of reaction rate vs time for the above reaction is shown below. The solid line reflects the forward reaction, while the broken line depicts the reverse reaction. Which one of the changes below explains the change in the graph at time X? A Temperature is decreased B Temperature is increased C Concentration of H 2 is decreased D Concentration of N 2 is increased. (2) 1.6 Consider the ionisation reaction: A conjugate acid-base pair is A NH 3 ; NH 4 + B NH 3 ; H 2 O C H 2 O ; NH 4 + NH 3 + H 2 O NH OH - D NH 3 ; OH - (2) 4

5 1.7 A 1 mol.dm -3 solution of each of a number of acids is prepared. Which solution will have the lowest ph? A HCl B H 2 SO 4 C CH 3 COOH D NH 4 OH. 1.8 Which ONE of the following reactions is spontaneous under standard conditions? (2) A Sn 4+ SO 2 + 2H 2 O Sn 2+ + SO H + B I 2 + 2Br - 2I - + Br 2 C 2 H 2 O O 2 + 2H 2 D 2Ag + + Fe 2+ 2Ag + Fe 3+. (2) 1.9 In the chlor-alkali membrane cell, brine is pumped into the cell. Which ONE of the following correctly indicates the products formed at the respective electrodes? Positive electrode Negative electrode A Cl 2 (g) Na (s) B OH - (aq) Na (s) C O 2 (g) H 2 (g) D Cl 2 (g) H 2 (g) (2) 1.10 Which fertilizer will best address the following needs of a crop? Increase tolerance to disease Assist with ripening of fruit A K 2 SO 4 H 2 NCONH 2 B KCl Ca 3 (H 2 PO 4 ) 2 C Ca 3 (H 2 PO 4 ) 2 KCl D NH 4 NO 3 Ca 3 (H 2 PO 4 ) 2 (2) [20] 5

6 QUESTION 2 The table below shows the vapour pressures of various organic compounds at 25 O C. 2.1 Write down Compound Molar mass (g mol -1 ) Vapour Pressure (x10 2 Pa) pentane ,0 hexane ,0 heptane ,0 propan-1-ol 60 21,0 propan-2-ol 60 44,0 butan-1-ol 74 6,2 butan-2-ol 74 18,3 pentan-1-ol 88 2,2 pentan-2-ol 88 8,04 ethanoic acid 60 15,3 propanone , the general formula of the homologous series of which heptane is a member. (1) the IUPAC name and structural formula of an isomer of pentane. (2) the structural formula of propanone. (2) 2.2 State and explain the relationship between vapour pressure and the strength of intermolecular forces. (3) 2.3 Explain the difference in vapour pressure between pentane, hexane and heptane. Refer to strength of intermolecular forces in your answer. (2) 2.4 Explain why: The vapour pressure of butan-1-ol is so much lower than that of pentane. (2) The vapour pressure of secondary alcohols are higher than the primary alcohols that has the same structural formula. (2) 2.5 Which compound will have the higher boiling point: ethanoic acid or propan-1-ol? (1) 2.6 Refer to vapour pressure, intermolecular forces and energy and give a reason for your answer to 2.5. (3) [18] 6

7 QUESTION 3 Bromine water can be used to distinguish between saturated and unsaturated compounds. Equal amounts of hex-2-ene and hexane are added to respective test tubes A and B at room temperature; 2cm 3 of bromine water is added to each and the test tubes shaken. The solution in test tube A becomes clearer, while the solution in test tube B has a brownish colour. 3.1 What is meant by an unsaturated compound? 3.2 Using structural formulas, write down the equation for the reaction in test tube A. 3.3 Name the reaction condition required for a reaction to take place in test tube B. (2) (3) (1) 3.4 Consider the flow diagram below: CH 2 CHCH 2 CH 3 reaction 1 2. hydration X 2-bromobutane 3. substitution 4. elimination eliminationn Y(main product) Name the type of reaction in reaction 1. (1) State the reaction condition required for reaction 2, whichh is the hydration reaction that forms compound X. (1) State the reaction conditions for reaction 3, that is the substitution reaction where X forms from 2-bromobutane. (2) Draw the structural formula of Y and give its IUPAC name. (2) 3.5 The diagram below shows the structural formula for polyethylene Write down the IUPAC name of the monomer that formed polyethylene State the type of polymerization that occurs when polyethylene is formed from its monomer. (1) (1) [14] 7

8 QUESTION 4 You are asked to do an investigation into how the concentration of reactants affects reaction rate. The reaction used for the investigation is that between sodium thiosulfate, Na 2 S 2 O 3, and hydrochloric acid (HCl). When combined, a substance is produced which causes the solution to become cloudy: Na 2 S 2 O 3 (aq) + 2HCl(aq) 2NaCl(aq) + S(s) + H 2 O(l) + SO 2 (g) List of chemicals: 250 ml of sodium thiosulfate solution; distilled water; hydrochloric acid solution of concentration 2 mol dm -3 Method: (incomplete) 1. Use a black pen to draw a large cross on a piece of paper 2. Put 50 ml of sodium thiosulfate solution into a conical flask. 3. Add 5 ml of hydrochloric acid, starting the stopwatch; swirl the mixture once or twice. 4. Place the reaction flask on the paper with the cross and note the time when the cross can no longer be seen. 5. Repeat the experiment but. 6. Repeat the experiment a third time but 7. Record the results in a table. Results: Experiment Time taken (s) 3,0 4,5 6,9 4.1 Give the definition of reaction rate. (1) 4.2 For the experiment described above, name the independent variable (1) dependant variable (1) 8

9 4.3 Consider the method: Rewrite points 5 and 6 describing what you would change each time so that the aim of the experiment can be achieved. (Note how the Time taken changes- do not be concerned with how much it changes). (3) What needs to be done in order to ensure that this is a fair test? (1) 4.4 Write down the name or formula of the substance responsible for the cloudiness. (1) 4.5 Consider the table of results: which experiment (1, 2 or 3) occurred at the highest reaction rate? (1) [9] QUESTION 5 The following equation represents a reaction in equilibrium 2-2CrO 4 (aq) + 2H + (aq) Cr 2 O 2-7 (aq) + H 2 O (l) yellow orange 5.1 Define chemical equilibrium. (2) 5.2 Is this an example of an open or closed system? (1) 5.3 A few drops of nitric acid (HNO 3 ) is added to the mixture What will the colour of the solution be? Write only ORANGE or YELLOW. (1) Give a reason for this observation. (2) 5.4 Write down the expression of the equilibrium constant (K c ) for this reaction. (2) 5.5 Will the addition of water have any influence on the value of the equilibrium constant. (1) 5.6 What colour will the solution be after a few pellets of sodium hydroxide (NaOH) is added to the solution? Write only ORANGE or YELLOW. (1) 5.7 Use Le Chatelier s Principle and explain the answer to Question 5.6. (3) [13] 9

10 QUESTION 6 Consider the equilibrium in a saturated solution of sodium chloride as shown by the equation below: NaCl(s) Na + (aq) + Cl - (aq) 6.1 Is the forward reaction exothermic or endothermic? (1) 6.2 At 25 O C, the solubility of sodium chloride is 35,9g per 100cm 3 water. Calculate the equilibrium constant for the system. (6) 6.3 What change to the reaction conditions will increase the value of K c for this reaction? Give an explanation for the answer. (4) 6.4 At the same temperature, the equilibrium constant of a saturated solution of silver chloride (AgCl) is 1,8x Is silver chloride more soluble or less soluble than sodium chloride at 25 O C? (1) [12] QUESTION 7 You are tasked to determine the percentage ethanoic acid (CH 3 COOH) in vinegar. 7,5g of commercial vinegar is dissolved in 100cm 3 water. 25cm 3 of this solution is neutralised by 28,5cm 3 of a sodium hydroxide (NaOH) solution of concentration 0,11mol dm -3. The balanced equation for the reaction is NaOH (aq) + CH 3 COOH (aq) CH 3 COONa + H 2 O 7.1 Calculate the ph of the sodium hydroxide solution. (5) 7.2 Calculate the number of moles sodium hydroxide used to neutralise the 25cm 3 of acid. (2) 7.3 Calculate the percentage ethanoic acid in the vinegar. (5) [12] 10

11 QUESTION 8 The industrial preparation of sulphuric acid (H 2SO 4) can be represented as follows: I II III IV S SO 2 SO 3 X H 2 SO Give the name of the industrial process used to prepare sulphuric acid. (1) 8.2 Give the name or formula of compound X. (1) 8.3 Give the name or formula of the catalyst used. (1) 8.4 Sulphuric acid is a strong acid. Define strong acid. (1) 8.5 Write an equation to illustrate how sulphuric acid ionises in water. (3) 8.6 Identify the conjugate acid in the equation in Question 8.5. (1) 8.7 Give the term used for the conjugate base in QUESTION 8.5 that is able to act as both a proton donor or a proton acceptor. (1) 8.8 Give the term used for an acid such as H 2 SO 4 that are able to donate two hydrogen ions per formula unit. (1) 8.9 Consider the following reaction of sulphuric acid: 2H 2 SO 4 + Cu CuSO 4 + 2H 2 O + SO 2 (g) The half reactions for this reaction is given as Cu Cu e - SO H + + 2e - 2H 2 O + SO Is sulphuric acid acting as an oxidising agent or reducing agent? (1) Explain the answer in QUESTION by referring to the oxidising reaction and electron transfer. (2) [13] 11

12 QUESTION 9 Consider the cell below which operates under standard conditions: V Fe Mg FeCl 3 (aq) KCl MgSO 4 (aq) MgCl 2 (aq) The nett cell reaction for this cell is 2 Fe Mg (s) 2 Fe (s) + 3 Mg What energy conversion takes place in this cell? (1) 9.2 State the standard conditions that will apply to this cell. (2) 9.3 Which electrode is the ANODE: Fe or Mg? (1) 9.4 Write down the oxidation half reaction for this cell. (3) 9.5 After the cell had been operating a while, it is determined that the mass of the magnesium plate changed by 0,96g. Calculate the change in mass of the iron electrode over the same period of time. (5) 9.6 A light bulb is marked 2 V. Calculate the emf of the cell and state whether or not the light bulb will burn if used in this circuit. Ignore internal resistance. (5) 9.7 How will the concentration of Mg 2+ -ions change while the cell is in operation? (1) 9.8 What effect, if any, will this change in Question 9.7 have on the voltmeter reading over a period of time? Give a reason for your answer. (2) [20] 12

13 QUESTION 10 Pure aluminium oxide (Al 2 O 3 ) is produced by the purification of ore that is mixed with molten cryolite. The aluminium oxide is used to produce Alumminium as shown in the diagram below. Alluminium is formed at the carbon lining. power supply graphite electrode carbon lining molten cryolite The net equation for this reaction is 4Al 3+ (l) + 6O 2- (l) 4Al(s) + 3O 2(g) molten aluminium 10.1 Name the ore in which aluminium oxide occurs. (1) 10.2 Consider the diagram: is this an electrolytic or galvanic cell? (1) 10.3 Are the carbon lining indicated in the diagram the anode or the cathode?. (1) 10.4 Must the carbon lining be connected to the positive or negative terminal of the power supply? (1) 10.5 Write down the half-reaction that occurs at the anode. (2) 10.6 Must the power supply be alternating current ( AC) or direct current (DC)? Give a reason for your answer.. (2) [8] 13

14 QUESTION 11 Ammonium nitrate is one of the inorganic fertilizers manufactured industrially. This flow-diagram illustrates the process. NH 3 X NO 2 HNO 3 Y NH 3 is produced industrially according to the following equation: N 2 (g) + 3H 2 (g) 2NH 3 (g) H < 0. According to Le Chatelier s Principle, ideal conditions for a maximum yield are a low temperature and a high pressure Name the process by which NH 3 is formed. (1) 11.2 The temperature at which process occurs is about 450 O C, which is relatively high. Give a reason why lower temperatures are NOT used. (1) 11.3 Identify compound X. (1) 11.4 Write down the balanced equation for the reaction in which NH 3 is turned into compound X. (2) 11.5 Write down the formula of the fertilizer Y. (1) 11.6 Scientists are concerned about pollution of the underground water by nitrate fertilizers. Give one reason why this pollution is dangerous for humans. (1) 11.7 A gardener finds an old 50kg bag of fertilizer. The label on the bag is partially worn (see diagram below). She has the contents analysed and It is determined that the percentage nitrogen in the bag is 18,75%. 5 : 2 : _ (30) 50 kg Determine the missing component in the N:P:K ratio. (4) [11] TOTAL:

15 NATIONAL SENIOR CERTIFICATE (CAPS) NASIONALE SENIOR SERTIFIKAAT (KABV) DATA FOR PHYSICAL SCIENCES GRADE 12 PAPER 2 (CHEMISTRY) GEGEWENS VIR FISIESE WETENSKAPPE GRAAD 12 VRAESTEL 2 (CHEMIE) TABLE 1: PHYSICAL CONSTANTS/TABEL 1: FISIESE KONSTANTES NAME/NAAM SYMBOL/SIMBOOL VALUE/WAARDE Standard pressure p Standaarddruk 1,013 x 10 5 Pa Molar gas volume at STP Molêre gasvolume by STD V m -1 22,4 dm 3 mol Standard temperature Standaardtemperatuur T 273 K Charge on electron e -1,6 x C TABLE 2: FORMULAE/TABEL 2: FORMULES Δm Δt m n= M n c = OR V m c = MV n = N N A V n= V m c V a a c V b b = n a n b K w = [H 3 O + ][OH - ] = 1 x at 298 K E cell = E cathode E anode E sel = E katode E anode E cell = E reduction E oxidation E sel = E reduksie E oksidasie E cell = E oxidisingagent E reducingagent E sel = E oksideermiddel E reduseermiddel 15

16 Physical Sciences/P2 16 CWED September 2014 NSC TABLE/TABEL 3: THE PERIODIC TABLE OF ELEMENTS/PERIODIEKE TABEL VAN ELEMENTE 1 (I) 2 (II) (III) 14 (IV) 15 (V) 16 (VI) 17 (VII) 18 (VIII) 2,1 1 H 1 2 He 4 1,0 3 Li 7 1,5 4 Be 9 2,0 5 B 11 2,5 6 C 12 3,0 7 N 14 3,5 8 O 16 4,0 9 F Ne 20 0,9 11 Na 23 1,2 12 Mg 24 1,5 13 Al 27 1,8 14 Si 28 2,1 15 P 31 2,5 16 S 32 3,0 17 Cl 35,5 18 Ar 40 0,8 19 K 39 1,0 20 Ca 40 1,3 21 Sc 45 1,5 22 Ti 48 1,6 23 V 51 1,6 24 Cr 52 1,5 25 Mn 55 1,8 26 Fe 56 1,8 27 Co 59 1,8 28 Ni 59 1,9 29 Cu 63,5 1,6 30 Zn 65 1,6 31 Ga 70 1,8 32 Ge 73 2,0 33 As 75 2,4 34 Se 79 2,8 35 Br Kr 84 0,8 37 Rb 86 1,0 38 Sr 88 1,2 39 Y 89 1,4 40 Zr Nb 92 1,8 42 Mo 96 1,9 43 Tc 2,2 44 Ru 101 2,2 45 Rh 103 2,2 46 Pd 106 1,9 47 Ag 108 1,7 48 Cd 112 1,7 49 In 115 1,8 50 Sn 119 1,9 51 Sb 122 2,1 52 Te 128 2,5 53 I Xe 131 0,7 55 Cs 133 0,9 56 Ba La 139 1,6 72 Hf Ta W Re Os Ir Pt Au Hg 201 1,8 81 Tl 204 1,8 82 Pb 207 1,9 83 Bi 209 2,0 84 Po 2,5 85 At 86 Rn 0,7 87 Fr 0,9 88 Ra Ac 58 Ce Pr Nd Pm 62 Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa 92 U Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 100 Fm 101 Md 102 No 103 Lr 29 Cu 63,5 1,9 Symbol Simbool Electronegativity Elektronegatiwiteit Approximate relative atomic mass Benaderde relatiewe atoommassa Atomic number Atoomgetal KEY/SLEUTEL

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18 Physical Sciences/P2 18 CWED September 2014 NSC TABLE 4A: STANDARD REDUCTION POTENTIALS/ TABEL 4A: STANDAARD REDUKSIEPOTENSIALE Increasing oxidising ability/toenemende oksiderende vermoë Half-reactions/Halfreaksies E (V) F 2(g) + 2e 2F + 2,87 Co 3+ + e Co ,82 MnO 4 + 8H+ + 5e Mn H 2O + 1,52 Cl 2(g) + 2e 2Cl + 1,36 Cr 2O H+ + 6e 2Cr H 2O + 1,33 MnO 2 + 4H + + 2e Mn H 2O + 1,28 O 2(g) + 4H + + 3e 2H 2O + 1,23 Br 2(l) + 2e 2Br + 1,06 NO 3 + 4H+ + 3e NO(g) + 2H 2O + 0,96 Ag + + e Ag + 0,80 Hg e Hg(l) + 0,78 NO 3 + 2H+ + e NO 2(g) + H 2O + 0,78 Fe 3+ + e Fe ,77 O 2(g) + 2H + + 2e H 2O 2 + 0,68 I 2 + 2e 2I + 0,54 Cu + + e Cu + 0,52 SO 2 + 4H + + 2e S + 2H 2O + 0,45 2H 2O + O 2 + 4e 4OH + 0,40 Cu e Cu + 0,34 SO H+ + 4e SO 2(g) + 2H 2O + 0,17 Cu 2+ + e Cu + + 0,16 Sn e Sn ,15 S + 2H + + 2e H 2S(g) + 0,14 2H + + 2e H 2(g) 0,00 Fe e Fe 0,04 Pb e Pb 0,13 Sn e Sn 0,14 Ni e Ni 0,25 Co e Co 0,28 Cd e Cd 0,40 Cr 3+ + e Cr 2+ 0,41 Fe e Fe 0,44 Cr e Cr 0,74 Cr e Cr 0,74 Zn e Zn 0,76 2H 2O + 2e H 2(g) + 2OH 0,83 Mn e Mn 1,18 Al e Al 1,66 Mg e Mg 2,37 Na + + e Na 2,71 Ca e Ca 2,87 Ba e Ba 2,90 K + + e K 2,92 Li + + e Li 3,04 Increasing reducing ability/toenemende reduserende vermoë

19 Increasing oxidising ability/toenemende oksiderende vermoë TABLE 4B: STANDARD REDUCTION POTENTIALS/ TABEL 4B: STANDAARD REDUKSIEPOTENSIALE Half-reactions/Halfreaksies E (V) Li + + e Li 3,04 K + + e K 2,92 Ba e Ba 2,90 Ca e Ca 2,87 Na + + e Na 2,71 Mg e Mg 2,37 Al e Al 1,66 Mn e Mn 1,18 2H 2O + 2e H 2(g) + 2OH 0,83 Zn e Zn 0,76 Cr e Cr 0,74 Cr e Cr 0,74 Fe e Fe 0,44 Cr 3+ + e Cr 2+ 0,41 Cd e Cd 0,40 Co e Co 0,28 Ni e Ni 0,25 Sn e Sn 0,14 Pb e Pb 0,13 Fe e Fe 0,04 2H + + 2e H 2(g) 0,00 S + 2H + + 2e H 2S(g) + 0,14 Sn e Sn ,15 Cu 2+ + e Cu + + 0,16 SO H+ + 4e SO 2(g) + 2H 2O + 0,17 Cu e Cu + 0,34 2H 2O + O 2 + 4e 4OH + 0,40 SO 2 + 4H + + 2e S + 2H 2O + 0,45 Cu + + e Cu + 0,52 I 2 + 2e 2I + 0,54 O 2(g) + 2H + + 2e H 2O 2 + 0,68 Fe 3+ + e Fe ,77 NO 3 + 2H+ + e NO 2(g) + H 2O + 0,78 Hg e Hg(l) + 0,78 Ag + + e Ag + 0,80 NO 3 + 4H+ + 3e NO(g) + 2H 2O + 0,96 Br 2(l) + 2e 2Br + 1,06 O 2(g) + 4H + + 3e 2H 2O + 1,23 MnO 2 + 4H + + 2e Mn H 2O + 1,28 Cr 2O H+ + 6e 2Cr H 2O + 1,33 Cl 2(g) + 2e 2Cl + 1,36 MnO 4 + 8H+ + 5e Mn H 2O + 1,52 Co 3+ + e Co ,82 F 2(g) + 2e 2F + 2,87 Increasing reducing ability/toenemende reduserende vermoë 19