NATIONAL SENIOR CERTIFICATE GRADE 12

Transcription

1 NTIONL SENIOR ERTIFITE GRE 12 PYSIL SIENES: EMISTRY (P2) FERURY/MR 2014 MRKS: 150 TIME: 3 hours This question paper consists of 13 pages and 4 data sheets. 3

2 Physical Sciences/P2 2 E/Feb. Mar 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/Feb. Mar 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 general name given to compounds formed when one or more hydrogen atoms in alkanes are replaced with halogens (1) 1.2 The homologous series of compounds with the general formula n 2n-2 (1) 1.3 The minimum energy needed for a reaction to occur (1) 1.4 The coating of one metal with another by the process of electrolysis (1) 1.5 The name of the industrial process used in the preparation of nitric acid (1) [5] QUESTION 2: MULTIPLE-OIE QUESTIONS Four options are given 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 compounds is a ketone? 3 O OO O 3 (O) 2 3 (2) 2.2 Which ONE of the following compounds is STURTE? 3 ( 3 ) ( 3 ) 2 2 (2) 2.3 scientist investigates a factor which influences the boiling points of alkanes. e determines the boiling points of the first six straight chain alkanes. Which ONE of the following is the independent variable in this investigation? oiling point Functional group ranching hain length (2)

4 oncentration Physical Sciences/P2 4 E/Feb. Mar The temperature of a substance is a measure of the... of the particles. average potential energy average kinetic energy total kinetic energy total potential energy (2) 2.5 The graph below shows a change made to a chemical equilibrium in a closed container at time t 1. The equation for the reaction is: N 2 (g) (g) 2N 3 (g) Δ < 0 2 (g) N 3 (g) N 2 (g) t 0 t 1 Time Which ONE of the following is the change made at time t 1? ddition of a catalyst Increase in temperature Increase in the concentration of N 2 (g) Increase in pressure by decreasing the volume (2) 2.6 In a chemical reaction, the difference between the potential energy of the products and the potential energy of the reactants is equal to the enthalpy of the reaction. rate of the reaction. enthalpy change of the reaction. total potential energy of the particles. (2)

5 Physical Sciences/P2 5 E/Feb. Mar onsider the galvanic cell represented below. Mg(s) Mg 2+ (aq) + (aq) 2 (g) Pt Which ONE of the following half-reactions takes place at the cathode? 2 (g) 2 + (aq) + 2e - Mg 2+ (aq) + 2e - Mg(s) Mg(s) Mg 2+ (aq) + 2e (aq) + 2e - 2 (g) (2) 2.8 onsider an electrochemical cell based on the following reaction: Sn 4+ (aq) + Sn(s) 2Sn 2+ (aq) Which ONE of the following statements regarding this cell is ORRET? Sn is the anode of the cell. Sn is the cathode of the cell. Sn 4+ (aq) is the reducing agent. Sn is the oxidising agent. (2) 2.9 Which ONE of the following statements regarding an electrolytic cell is ORRET? n electric current causes a chemical change to occur. Reduction occurs at the anode. spontaneous chemical reaction produces an electric current. Electrons flow to the electrode where oxidation occurs. (2) 2.10 Which ONE of the following is formed at the cathode in a membrane cell? hlorine ydrogen Sodium chloride Oxygen (2) [20] TOTL SETION : 25

6 Physical Sciences/P2 6 E/Feb. Mar 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 your 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 O butan-2-ol 3 pentanal E 2 5 O F methyl propanoate 3.1 Write down the letter that represents a compound that: Is unsaturated (1) Is a structural isomer of compound (1) Is an aldehyde (1) elongs to the same homologous series as compound (1) 3.2 Write down the: IUP name of compound (2) Structural formula of compound (2) Name of the homologous series to which compound F belongs (1)

7 Physical Sciences/P2 7 E/Feb. Mar ompound reacts with compound E in an acid catalysed condensation reaction. Write down the: General name given to this reaction (1) Structural formula of the organic product formed (2) IUP name of compound (1) [13] QUESTION 4 (Start on a new page.) Petrol is a mixture of hydrocarbons, many of which have the molecular formula Write down the name of the homologous series to which hydrocarbons with this molecular formula belong. (1) The structures of two compounds with molecular formula 8 18 are given below. ompound ompound 4.2 Why are compounds and structural isomers? (2) 4.3 Which ONE of the above compounds ( or ) has a higher boiling point? Refer to MOLEULR STRUTURE, INTERMOLEULR FORES and the ENERGY NEEE to explain the answer. (4) 4.4 ompounds and can be used to prepare smaller hydrocarbons at high temperatures in the presence of a catalyst. One such reaction is represented by the incomplete equation below. Write down the: compound Name of the reaction represented above (1) Structural formula of compound (2) alanced equation, using molecular formulae, for the complete combustion of 5 12 (3) [13]

8 Physical Sciences/P2 8 E/Feb. Mar QUESTION 5 (Start on a new page.) The flow diagram below shows the steps that a learner follows to convert but-1-ene to but-2-ene. ut-1-ene ompound X (Major product) ompound Z 3 (O) 2 3 ut-2-ene 5.1 Write down the structural formula of the functional group of but-1-ene. (1) 5.2 ompound X is formed when but-1-ene reacts with l(g) Name the type of reaction that takes place. (1) Write down the structural formula of compound X. (2) 5.3 ompound X is converted to alcohol Z Name the type of reaction that takes place. (1) Write down the NME or FORMUL of another reactant needed for this reaction. (1) 5.4 ompound Z is converted to but-2-ene in the presence of concentrated sulphuric acid Is compound Z a PRIMRY, SEONRY or TERTIRY alcohol? (1) Name the type of reaction that takes place. (1) What is the role of sulphuric acid in this reaction? (1) 5.5 nother learner discovers that but-2-ene can be prepared using the following incomplete reaction below. Write down the: ompound X + (a) but-2-ene + (b) + (c) Type of reaction that takes place (1) onditions needed for this reaction to take place (2) FORMULE of the reactant and products represented by each of the letters (a), (b) and (c) respectively (3) [15]

9 oncentration of P (mol dm -3 ) Physical Sciences/P2 9 E/Feb. Mar QUESTION 6 (Start on a new page.) The graph below shows the decomposition of gas P according to the following equation: P(g) 2Q(g) + R(g) Δ < 0 Graph of concentration of P versus time 0,25 0,20 0,15 0,10 0, Time (s) efine the term rate of reaction in words by referring to the graph. (2) 6.2 t which time, 10 s or 30 s, does the decomposition take place at a higher rate? Refer to the graph to give a reason for the answer. (2) 6.3 Write down the initial concentration of P(g). (1) 6.4 The decomposition is carried out in a 2 dm 3 container. alculate the average rate (in mol s -1 ) at which P(g) is decomposed in the first 10 s. (6)

10 Physical Sciences/P2 10 E/Feb. Mar raw a potential energy diagram for the reaction. learly indicate the following on the diagram: Positions of the reactants and products ctivation energy (E a ) for the forward reaction (3) 6.6 n increase in temperature will increase the rate of decomposition of P(g). Explain this statement in terms of the collision theory. (2) [16] QUESTION 7 (Start on a new page.) The reaction of methane gas ( 4 ) with steam ( 2 O) produces hydrogen gas. The equation for the reaction is shown below. 4 (g) O(g) O 2 (g) (g) 7.1 riefly explain why the O 2 gas may be harmful to the environment. (2) Initially, 1 mol of methane and 2 mol of steam are sealed in a 5,0 dm 3 container. When equilibrium is established at temperature T 1, the mixture contains 0,3 mol of O 2 (g). 7.2 efine the term chemical equilibrium. (2) 7.3 alculate the equilibrium constant (K ) at T 1. (7) 7.4 new equilibrium is now established at a higher temperature T 2. The value of the equilibrium constant (K ) at this new temperature is 0,01. Is this reaction exothermic or endothermic? Use Le hatelier's principle and the value of K at T 1 and T 2 to explain the answer. (4) [15]

11 Physical Sciences/P2 11 E/Feb. Mar QUESTION 8 (Start on a new page.) The diagram below represents a galvanic cell operating under standard conditions. V u(s) g(s) salt bridge u(no 3 ) 2 (aq) - (aq) gno 3 (aq) 8.1 Write down: The energy conversion which takes place in this cell (1) balanced equation for the overall cell reaction (3) The cell notation for this cell (3) 8.2 alculate the initial emf of this cell. (4) 8.3 In which direction will electrons flow? Write down only 'from g to u' or 'from u to g'. (1) 8.4 The cell is allowed to discharge for a period of time during which the mass of the copper electrode changes by 3,2 g. alculate the expected mass change of the silver electrode. (ssume that the change in mass is only a result of the oxidation-reduction reaction occurring as the cell discharges.) (4) 8.5 The silver half-cell is now replaced with the standard hydrogen half-cell Is the copper electrode the POSITIVE or the NEGTIVE electrode? Refer to the relative strength of reducing agents to explain the answer. (4) Write down the emf of this cell. (1) [21]

12 Physical Sciences/P2 12 E/Feb. Mar QUESTION 9 (Start on a new page.) The diagram below represents the apparatus used in the electrolysis of a concentrated ul 2 solution. and are two carbon electrodes connected to a power supply. + _ concentrated ul 2 (aq) 9.1 Which electrode ( or ) is the anode? (1) 9.2 Is the electrolytic process endothermic or exothermic? (1) 9.3 Write down TREE observations that can be made during this process. (3) 9.4 Write down the overall cell reaction. (3) 9.5 Give ONE reason why the salt needs to be in solution in this process. (1) [9] QUESTION 10 (Start on a new page.) hydrogen-oxygen fuel cell consists of an electrolytic solution such as potassium hydroxide and two inert electrodes. ydrogen and oxygen are bubbled into the cell and the following half-reactions occur: 2 (g) + 2O - (aq) 2 2 O(l) + 2e - O 2 (g) O(l) + 4e - 4O - (aq) 10.1 Write down the overall cell reaction for this cell. (3) 10.2 Give a reason why this cell is regarded as environmentally friendly. (1) 10.3 alculate the initial emf of this cell. (4) 10.4 alculate the energy stored in the cell if it has a capacity of 1 h. (5) [13]

13 Physical Sciences/P2 13 E/Feb. Mar QUESTION 11 (Start on a new page.) Sulphuric acid is produced by the contact process and is used in the production of fertilisers such as ammonium sulphate In one of the steps in this process, sulphur trioxide is dissolved in sulphuric acid rather than in water to produce oleum Write down a balanced equation showing how oleum is produced. (3) Give a reason why sulphur trioxide is not dissolved in water to produce sulphuric acid. (1) 11.2 farmer wants to use a fertiliser which promotes root growth in his vegetable garden. e must choose between ammonium sulphate, ammonium nitrate and ammonium phosphate. The percentage of the elements in each of the fertilisers is given in the table below. ELEMENT MMONIUM MMONIUM MMONIUM SULPTE NITRTE POSPTE Nitrogen 21, ,19 Sulphur 24, Phosphorous , Which ONE of the above fertilisers will be the best choice? Refer to the data in the table to give a reason for the answer. (2) Write down TWO negative impacts of the overuse of fertiliser on the environment. (4) [10] TOTL SETION : GRN TOTL:

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15 Physical Sciences/P2 1 E/Feb. Mar 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 Standaarddruk Molar gas volume at STP Molêre gasvolume by ST Standard temperature Standaardtemperatuur harge on electron Lading op elektron p 1,013 x 10 5 Pa V m 22,4 dm 3 mol -1 T e 273 K -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 / oxidisingagent reducingagent E sel E oksideermiddel E reduseermiddel

16 Physical Sciences/P2 2 E/Feb. Mar 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 Electronegativity Elektronegatiwiteit pproximate relative atomic mass enaderde relatiewe atoommassa tomic number toomgetal 29 u 63,5 1,9 Symbol Simbool KEY/SLEUTEL

17 Increasing oxidising ability/toenemende oksiderende vermoë Increasing reducing ability/toenemende reduserende vermoë Physical Sciences/P2 3 E/Feb. Mar TLE 4: STNR REUTION POTENTILS TEL 4: STNR-REUKSIEPOTENSILE alf-reactions/alfreaksies E (V) F 2(g) + 2e 2F + 2,87 o 3+ + e o ,81 2O e 2 2O +1,77 MnO e Mn O + 1,51 l 2(g) + 2e 2l + 1,36 r 2O e 2r O + 1,33 O 2(g) e 2 2O + 1,23 MnO e Mn O + 1,23 Pt e Pt + 1,20 r 2(l) + 2e 2r + 1,07 NO e NO(g) + 2 2O + 0,96 g e g(l) + 0,85 g + + e g + 0,80 NO e NO 2(g) + 2O + 0,80 Fe 3+ + e Fe ,77 O 2(g) e 2O 2 + 0,68 I 2 + 2e 2I + 0,54 u + + e u + 0,52 SO e S + 2 2O + 0,45 2 2O + O 2 + 4e 4O + 0,40 u e u + 0,34 SO e SO 2(g) + 2 2O + 0,17 u 2+ + e u + + 0,16 Sn e Sn ,15 S e 2S(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 0,76 2 2O + 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

18 Increasing oxidising ability/toenemende oksiderende vermoë Increasing reducing ability/toenemende reduserende vermoë Physical Sciences/P2 4 E/Feb. Mar TLE 4: STNR REUTION POTENTILS TEL 4: STNR-REUKSIEPOTENSILE alf-reactions/alfreaksies E (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 0,91 2 2O + 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 2S(g) + 0,14 Sn e Sn ,15 u 2+ + e u + + 0,16 SO e SO 2(g) + 2 2O + 0,17 u e u + 0,34 2 2O + O 2 + 4e 4O + 0,40 SO e S + 2 2O + 0,45 u + + e u + 0,52 I 2 + 2e 2I + 0,54 O 2(g) e 2O 2 + 0,68 Fe 3+ + e Fe ,77 NO e NO 2(g) + 2O + 0,80 g + + e g + 0,80 g e g(l) + 0,85 NO e NO(g) + 2 2O + 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 2O + 1,23 r 2O e 2r O + 1,33 l 2(g) + 2e 2l + 1,36 MnO e Mn O + 1,51 2O e 2 2O +1,77 o 3+ + e o ,81 F 2(g) + 2e 2F + 2,87