NATIONAL SENIOR CERTIFICATE GRADE 12

Transcription

1 NTIONL SENIOR ERTIFITE GRE 12 PYSIL SIENES: EMISTRY (P2) NOVEMER 2011 MRKS: 150 TIME: 3 hours This question paper consists of 15 pages and 4 data sheets.

2 Physical Sciences/P2 2 E/November 2011 INSTRUTIONS N INFORMTION Write your centre number and examination number in the appropriate spaces on the NSWER OOK. nswer LL the questions in the NSWER OOK. This question paper consists of TWO sections: SETION (25) SETION (125) You may use a non-programmable calculator. You may use appropriate mathematical instruments. Number the answers correctly according to the numbering system used in this question paper. ata sheets and a periodic table are attached for your use. Give brief motivations, discussions, et cetera where required. Round off your final numerical answers to a minimum of TWO decimal places.

3 Physical Sciences/P2 3 E/November 2011 SETION QUESTION 1: ONE-WOR ITEMS Give ONE word/term for each of the following descriptions. Write only the word/term next to the question number ( ) in the NSWER OOK. 1.1 The homologous series to which the compound 3 l belongs (1) 1.2 The general term that describes compounds that consist of hydrogen and carbon atoms only (1) 1.3 The stage reached in a reversible chemical reaction when the rate of the forward reaction is equal to the rate of the reverse reaction (1) 1.4 The name of the chemical substance in which l 2 O 3 is dissolved to lower its melting point during the industrial extraction of aluminium (1) 1.5 The ability of a cell to store charge (1) [5] QUESTION 2: MULTIPLE-OIE QUESTIONS Four options are provided as possible answers to the following questions. Each question has only ONE correct answer. Write only the letter ( ) next to the question number ( ) in the NSWER OOK. 2.1 Which ONE of the following general formulae represents alkynes? n 2n+2 n 2n-2 n 2n n 2n-1 (2) 2.2 Which ONE of the following homologous series does NOT contain a RONYL group ( O )? ldehydes lcohols arboxylic acids Esters (2)

4 Physical Sciences/P2 4 E/November The structures of four organic compounds are shown below. I 3 II 3 2 O O 3 III 3 3 IV O 3 2 O Which of the above compounds have the same IUP name? I and II only III and IV only I and III only II and IV only (2) 2.4 The reaction represented by the equation below reaches equilibrium. 2rO 2 (aq) (aq) r 2 O 2 (aq) + 7 2O(l) yellow orange Which ONE of the following changes to the reaction mixture will change its colour from yellow to orange? dd a catalyst. dd water to the reaction mixture. dd a few drops of sodium hydroxide solution to the reaction mixture. dd a few drops of concentrated hydrochloric acid to the reaction mixture. (2)

5 Physical Sciences/P2 5 E/November The Maxwell-oltzmann energy distribution curves below show the number of particles as a function of their kinetic energy for a reaction at four different temperatures. The minimum kinetic energy needed for effective collisions to take place is represented by E. Number of particles E Kinetic energy Which ONE of these curves represents the reaction with the highest rate? (2) 2.6 certain chemical reaction is represented by the potential energy diagram below. Potential energy (kj) E 1 E a E 2 ourse of reaction Which ONE of the following quantities will change when a catalyst is added? E 2 E 1 E a (2)

6 Physical Sciences/P2 6 E/November When a metallic atom becomes an ion, it loses electrons and is oxidised. loses electrons and is reduced. gains electrons and is oxidised. gains electrons and is reduced. (2) 2.8 Which ONE of the following substances NNOT be used as a fertiliser? Nitrogen gas Guano one meal mmonium sulphate (2) 2.9 onsider the two half-reactions below that occur in a battery. Zn(s) + 2O - (aq) ZnO(s) + 2 O(l) + 2e - g 2 O(s) + 2 O(l) +2e - 2g(s) +2O - (aq) Which ONE of the following statements is ORRET? g(s) is reduced. Zn(s) is the anode. g 2 O(s) is the negative electrode. Electrons are transferred from g(s) to Zn(s). (2) 2.10 The oxidation number of copper (u) in the compound uso 4 is (2) [20] TOTL SETION : 25

7 Physical Sciences/P2 7 E/November 2011 SETION INSTRUTIONS Start E question on a NEW page. Leave ONE line between two subquestions, for example between QUESTION 3.1 and QUESTION 3.2. Show the formulae and substitutions in LL calculations. Round off LL final numerical answers to a minimum of TWO decimal places. QUESTION 3 (Start on a new page.) The letters to F in the table below represent six organic compounds. O 2 2 O 2 E F ethyl butanoate 3.1 Write down the letter that represents the following: ketone (1) compound which is an isomer of prop-1-ene (1) 3.2 Write down the IUP name of the following: ompound (2) ompound (2) 3.3 Write down the NME or FORMUL of E of the TWO products formed during the complete combustion of compound E. (2)

8 Physical Sciences/P2 8 E/November ompound F is the organic product of the reaction between a carboxylic acid and ethanol. Write down the following: The name of the homologous series to which compound F belongs (1) The structural formula of the FUNTIONL GROUP of carboxylic acids (1) The IUP name of the carboxylic acid from which compound F is prepared (2) The structural formula of compound F (2) [14] QUESTION 4 (Start on a new page.) Three hydrocarbons (, and ) with molecular formula 5 12 are used to investigate the effect of RNING on the OILING POINTS of hydrocarbons. The results obtained are shown in the table below. YRORON OILING POINT ( ) Write down the term used to describe compounds with the same molecular formula, but with different structural formulae. (1) 4.2 Write down for this investigation the following: ependent variable (1) Independent variable (1) ontrolled variable (1) 4.3 re these hydrocarbons saturated or unsaturated? Explain the answer. (3) 4.4 One of the hydrocarbons (, or ) has a straight chain with no branches. Write down the following: The letter (, or ) that represents this hydrocarbon (1) Its IUP name (2)

9 Physical Sciences/P2 9 E/November onsider hydrocarbon and its boiling point Write down the structural formula of hydrocarbon. (2) Explain why hydrocarbon has the lowest boiling point. In your explanation, refer to its structure, intermolecular forces and the energy involved. (3) 4.6 Which ONE of hydrocarbons (, or ) has the highest vapour pressure? Refer to the data in the table to give a reason for the answer. (2) [17] QUESTION 5 (Start on a new page.) In the flow diagram below R, P and Q represent different types of reactions. 3 2 P lcohol X (major product) R 3 r 3 Q lcohol Y 5.1 Name the type of reaction represented by: P Q R (1) (1) (1) 5.2 Using structural formulae, write down a balanced equation for reaction P. (4) 5.3 Write down the IUP name of alcohol Y. (2) 5.4 Reaction Q takes place in the presence of a SE. Write down TWO reaction conditions for this reaction. (2) [11]

10 Physical Sciences/P2 10 E/November 2011 QUESTION 6 (Start on a new page.) Learners use copper(ii) oxide POWER to decompose hydrogen peroxide. They add 1 g copper(ii) oxide to 100 cm 3 hydrogen peroxide in a flask connected to a delivery tube. The reaction that takes place is represented by the following balanced equation: uo(s) 2 2 O 2 (l) 2 2 O(l) + O 2 (g) 6.1 Write down the name of ONE item of apparatus that can be used to measure the volume of the gas produced. (1) The volume of oxygen gas produced is measured every 10 seconds. The results obtained are shown in the graph below. Volume of oxygen gas (cm 3 ) Time (s) 6.2 Use the graph to determine the volume of oxygen gas collected in the container at 15 seconds. (2) 6.3 ow does the rate of the reaction change between t = 40 s and t = 70 s? Write down only INRESES, ERESES or REMINS TE SME. Refer to the graph to explain the answer. (2) 6.4 What is the function of the copper(ii) oxide in this reaction? (1) 6.5 part from oxygen, write down the NMES or FORMULE of TWO substances present in the flask after 90 seconds. (2) 6.6 The learners found that oxygen is produced at a slower rate when 1 g of a SOLI LUMP of copper(ii) oxide is used. Fully explain this observation. (2) 6.7 It is known that bad breath is due to bacterial activity in the mouth in the absence of oxygen. Use the reaction above to explain why a solution containing hydrogen peroxide can be used as mouthwash to improve bad breath. (2) [12]

11 Physical Sciences/P2 11 E/November 2011 QUESTION 7 (Start on a new page.) 7.1 The industrial preparation of hydrogen gas is represented by the equation below. 4 (g) + 2 O(g) O(g) (g) > 0 The reaction reaches equilibrium at in a closed container State Le hatelier's principle. (3) ow will an increase in pressure at (by decreasing the volume) affect the yield of hydrogen gas? Write down only INRESES, ERESES OR NO EFFET. Explain the answer. (3) Give TWO reasons why high temperatures are used for this reaction. (2) 7.2 Study the reversible reaction represented by the balanced equation below. 2 (g) + O 2 (g) 2 O(g) + O(g) Initially x moles of 2 (g) is mixed with 0,3 moles of O 2 (g) in a sealed 10 dm 3 container. When equilibrium is reached at a certain temperature, it is found that 0,2 moles of 2 O(g) is present. The equilibrium constant (K c ) for the reaction at this temperature is alculate the initial number of moles of 2 (g), x, that was in the container. (8) The reaction is now carried out at a much higher temperature. It is found that K c decreases at this higher temperature. Is this reaction exothermic or endothermic? Explain the answer. (3) [19]

12 Physical Sciences/P2 12 E/November 2011 QUESTION 8 (Start on a new page.) The potential difference of a galvanic cell, measured experimentally by learners, is OMPRE with its potential difference calculated at standard conditions. They set up the galvanic cell shown below. V u salt bridge Pb u 2+ (aq) Pb 2+ (aq) The voltmeter measures an initial reading of 0,3 V. 8.1 Write down the energy conversion that takes place in this cell. (1) 8.2 State ONE function of the salt bridge. (1) 8.3 Write down the half-reaction that takes place at the anode. (2) 8.4 In which direction do electrons flow in the external circuit when this cell delivers a current? Write down only 'from u to Pb' or 'from Pb to u'. (1) 8.5 Write down the balanced net (overall) cell reaction. (3) 8.6 Is the cell reaction exothermic or endothermic? (1) 8.7 Use the Table of Standard Reduction Potentials to calculate the initial potential difference (emf) of the above cell at STNR ONITIONS. (4) 8.8 From the results obtained the learners conclude that the measured potential difference differs from the calculated potential difference. Give TWO possible reasons for this difference in values. (4) [17]

13 Physical Sciences/P2 13 E/November 2011 QUESTION 9 (Start on a new page.) In the electrolytic cell, represented below, two RON ROS are used as electrodes and a concentrated copper(ii) chloride solution is used as electrolyte. battery P Q ul 2 (aq) When the cell is functioning, a gas is released at electrode P, whilst electrode Q is coated with a reddish brown layer. 9.1 efine the term electrolyte. (2) 9.2 Write down a half-reaction to explain the observation made at: Electrode P (2) Electrode Q (2) 9.3 Which electrode, P or Q, is the cathode? Give a reason for the answer. (2) 9.4 The carbon rods in the above cell are now replaced with OPPER ROS. The following observations are made at electrode P: No gas is released. Its surface appears rough and eroded Refer to the RELTIVE STRENGTS OF REUING GENTS to explain this observation. (3) This cell can be used for the refining of copper. Which electrode (P or Q) will be replaced with impure copper during the refining process? (1) [12]

14 Physical Sciences/P2 14 E/November 2011 QUESTION 10 (Start on a new page.) The simplified diagram of a membrane cell used in the chlor-alkali industry is shown below. Gas, gas and compound are the three major products formed during this process. X and Y represent the two electrodes. Gas Membrane Gas Water rine ompound X Y Used salt solution Power supply 10.1 Write down the function of the membrane in this cell. (1) 10.2 Which electrode, X or Y, is connected to the positive terminal of the power supply? riefly explain how you arrived at the answer. (2) 10.3 Write down the NME or FORMUL of: Gas (1) Gas (1) ompound (1) 10.4 Write down the balanced net (overall) cell reaction taking place in this cell. (3) 10.5 The chlor-alkali industry is sometimes blamed for contributing to the greenhouse effect. riefly explain how the above cell contributes to the greenhouse effect. (2) [11]

15 Physical Sciences/P2 15 E/November 2011 QUESTION 11 (Start on a new page.) Nitric acid is used in the preparation of fertiliser. The flow diagram below shows the three steps (, and ) in the industrial preparation of nitric acid. N 3 (g) Nitrogen(II) oxide NO O 2 O 2 (g) 2 O 2 NO 3 (l) 11.1 Write down the following: Name of this industrial process in the preparation of nitric acid (1) alanced equation for step (3) 11.2 N 3 (g) reacts with O 2 (g) to form two products in step. One of the products is nitrogen(ii) oxide. Write down the NME or FORMUL of the OTER product. (1) 11.3 In step, water is added to the reaction mixture. This step can be represented by the following incomplete equation: NO 2 (g) O(l) NO 3 (l) opy the above incomplete equation into your NSWER OOK, fill in the missing reactant and balance the equation. (2) kg bag of fertiliser is labelled as shown in the diagram below (30) alculate the mass of nitrogen present in this bag of fertiliser. (3) 11.5 Uncontrolled use of fertiliser may cause excess fertiliser to run down into streams and rivers, leading to eutrophication. State ONE negative impact that eutrophication in water may have on humans. (2) [12] TOTL SETION : GRN TOTL:

16 Physical Sciences/P2 E/November 2011 T FOR PYSIL SIENES GRE 12 PPER 2 (EMISTRY) GEGEWENS VIR FISIESE WETENSKPPE GR 12 VRESTEL 2 (EMIE) TLE 1: PYSIL ONSTNTS/TEL 1: FISIESE KONSTNTES NME/NM SYMOL/SIMOOL VLUE/WRE Standard pressure p Standaarddruk 1,013 x 10 5 Pa Molar gas volume at STP Molêre gasvolume by ST V m 22,4 dm 3 mol -1 Standard temperature Standaardtemperatuur T 273 K harge on electron Lading op elektron e -1,6 x TLE 2: FORMULE/TEL 2: FORMULES n c = V m n= M or/of m c = MV E = E E / cell cathode anode E sel = E katode E anode q = I t W = Vq or/of E cell or/of = E E / reduction oxidation E sel = E reduksie E oksidasie E cell = E E / oxidising agent reducing agent E sel = E oksideermiddel E reduseermiddel

17 Physical Sciences/P2 E/November 2011 TLE 3: TE PERIOI TLE OF ELEMENTS TEL 3: IE PERIOIEKE TEL VN ELEMENTE 1 (I) 2 (II) (III) 14 (IV) 15 (V) 16 (VI) 17 (VII) 18 (VIII) 2, e 4 1,0 3 Li 7 1,5 4 e 9 2, , ,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 l 27 1,8 14 Si 28 2,1 15 P 31 2,5 16 S 32 3,0 17 l 35,5 18 r 40 0,8 19 K 39 1,0 20 a 40 1,3 21 Sc 45 1,5 22 Ti 48 1,6 23 V 51 1,6 24 r 52 1,5 25 Mn 55 1,8 26 Fe 56 1,8 27 o 59 1,8 28 Ni 59 1,9 29 u 63,5 1,6 30 Zn 65 1,6 31 Ga 70 1,8 32 Ge 73 2,0 33 s 75 2,4 34 Se 79 2,8 35 r 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 g 108 1,7 48 d 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 s 133 0,9 56 a La 139 1,6 72 f Ta W Re Os Ir Pt u g 201 1,8 81 Tl 204 1,8 82 Pb 207 1,9 83 i 209 2,0 84 Po 2,5 85 t 86 Rn 0,7 87 Fr 0,9 88 Ra c 58 e Pr Nd Pm 62 Sm Eu Gd Tb y o Er Tm Yb Lu Th Pa 92 U Np 94 Pu 95 m 96 m 97 k 98 f 99 Es 100 Fm 101 Md 102 No 103 Lr tomic number toomgetal 29 u 63,5 1,9 Symbol Simbool Electronegativity Elektronegatiwiteit pproximate relative atomic mass enaderde relatiewe atoommassa KEY/SLEUTEL

18 Physical Sciences/P2 E/November 2011 TLE 4: STNR REUTION POTENTILS TEL 4: STNR-REUKSIEPOTENSILE Increasing oxidising ability/toenemende oksiderende vermoë alf-reactions/alfreaksies E (V) F 2 (g) + 2e 2F + 2,87 o 3+ + e o ,81 2 O e 2 2 O +1,77 MnO e Mn O + 1,51 l 2 (g) + 2e 2l + 1,36 r 2 O e 2r O + 1,33 O 2 (g) e 2 2 O + 1,23 MnO e Mn O + 1,23 Pt e Pt + 1,20 r 2 (l) + 2e 2r + 1,07 NO e NO(g) O + 0,96 g e g(l) + 0,85 g + + e g + 0,80 NO e NO 2 (g) + 2 O + 0,80 Fe 3+ + e Fe ,77 O 2 (g) e 2 O 2 + 0,68 I 2 + 2e 2I + 0,54 u + + e u + 0,52 SO e S O + 0, O + O 2 + 4e 4O + 0,40 u e u + 0,34 SO e SO 2 (g) O + 0,17 u 2+ + e u + + 0,16 Sn e Sn ,15 S e 2 S(g) + 0, e 2 (g) 0,00 Fe e Fe 0,06 Pb e Pb 0,13 Sn e Sn 0,14 Ni e Ni 0,27 o e o 0,28 d e d 0,40 r 3+ + e r 2+ 0,41 Fe e Fe 0,44 r e r 0,74 Zn e Zn 0, O + 2e 2 (g) + 2O 0,83 r e r 0,91 Mn e Mn 1,18 l e l 1,66 Mg e Mg 2,36 Na + + e Na 2,71 a e a 2,87 Sr e Sr 2,89 a e a 2,90 s + + e - s - 2,92 K + + e K 2,93 Li + + e Li 3,05 Increasing reducing ability/toenemende reduserende vermoë

19 E Physical Sciences/P2 E/November 2011 TLE 4: STNR REUTION POTENTILS TEL 4: STNR-REUKSIEPOTENSILE alf-reactions/alfreaksies (V) Li + + e Li 3,05 K + + e K 2,93 s + + e s 2,92 a e a 2,90 Sr e Sr 2,89 a e a 2,87 Na + + e Na 2,71 Mg e Mg 2,36 l e l 1,66 Mn e Mn 1,18 r e r 0, O + 2e 2 (g) + 2O 0,83 Zn e Zn 0,76 r e r 0,74 Fe e Fe 0,44 r 3+ + e r 2+ 0,41 d e d 0,40 o e o 0,28 Ni e Ni 0,27 Sn e Sn 0,14 Pb e Pb 0,13 Fe e Fe 0, e 2 (g) 0,00 S e 2 S(g) + 0,14 Sn e Sn ,15 u 2+ + e u + + 0,16 SO e SO 2 (g) O + 0,17 Increasing oxidising ability/toenemende oksiderende vermoë u e u + 0, O + O 2 + 4e 4O + 0,40 SO e S O + 0,45 u + + e u + 0,52 I 2 + 2e 2I + 0,54 O 2 (g) e 2 O 2 + 0,68 Fe 3+ + e Fe ,77 NO e NO 2 (g) + 2 O + 0,80 g + + e g + 0,80 g e g(l) + 0,85 NO e NO(g) O + 0,96 r 2 (l) + 2e 2r + 1,07 Pt e Pt + 1,20 MnO e Mn O + 1,23 O 2 (g) e 2 2 O + 1,23 r 2 O e 2r O + 1,33 l 2 (g) + 2e 2l + 1,36 MnO e Mn O + 1,51 2 O e 2 2 O +1,77 o 3+ + e o ,81 F 2 (g) + 2e 2F + 2,87 Increasing reducing ability/toenemende reduserende vermoë