NATIONAL SENIOR CERTIFICATE GRADE 12

Transcription

1 NTIONL SENIOR ERTIFITE GRE 12 PYSIL SIENES: EMISTRY (P2) EXEMPLR 2014 MRKS: 150 TIME: 3 hours This question paper consists of 15 pages and 4 data sheets.

2 Physical Sciences/P2 2 E/2014 INSTRUTIONS N INFORMTION Write your name in the appropriate space on the NSWER OOK. This question paper consists of TEN questions. nswer LL the questions in the NSWER OOK. Start E question on a NEW page in the NSWER OOK. Number the answers correctly according to the numbering system used in this question paper. Leave ONE line between two subquestions, for example between QUESTION 2.1 and QUESTION 2.2. You may use a non-programmable calculator. You may use appropriate mathematical instruments. You are advised to use the attached T SEETS. Show LL formulae and substitutions in LL calculations. Round off your final numerical answers to a minimum of TWO decimal places. Give brief motivations, discussions, et cetera where required. Write neatly and legibly.

3 Physical Sciences/P2 3 E/2014 QUESTION 1: 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, for example 1.11 E. 1.1 The primary nutrient needed by plants for the promotion of root growth is nitrogen. phosphorus. potassium. calcium. (2) 1.2 The rate of a chemical reaction can be expressed in grams per mole. energy consumed per mole. volume of gas formed per unit time. moles of product formed per litre of solution. (2) 1.3 Which ONE of the compounds below is an aldehyde? 3 O 3 O 3 3 OO 3 O (2) 1.4 The reaction represented by the equation below takes place in the presence of a catalyst (l) 2 4 (g) (g) (l) This reaction is an example of addition. cracking. substitution. polymerisation. (2)

4 Physical Sciences/P2 4 E/ Which ONE of the following graphs shows the relationship between activation energy (E a ) of a reaction and temperature? E a E a 0 E a Temperature 0 E a Temperature 0 Temperature 0 Temperature (2) 1.6 Which ONE of the following NNOT act as a reducing agent? Mg r Fe 2+ MnO 4 (2)

5 Physical Sciences/P2 5 E/ onsider the structural formula of an organic compound below. Which ONE of the following is the correct IUP name of this compound? 2,2,4-trimethylpent-2-ene 2,2,4-trimethylpent-3-ene 2,4,4-trimethylpent-2-ene 2,4,4-trimethylpent-3-ene (2) 1.8 sample of silver contains impurities of gold. uring purification by electrolysis, the impure silver is used as an electrode. Which ONE of the following is the best choice of anode and cathode for this process? TOE NOE Pure gold Impure silver Impure silver Pure gold Pure silver Impure silver Impure silver Pure silver (2)

6 Physical Sciences/P2 6 E/ Initially, a certain amount of Il(g) is sealed in an empty flask at a certain temperature. The reaction that takes place is: 2Il(g) I 2 (g) + l 2 (g) Which of the following statements describe(s) the change(s) occurring as the system proceeds towards equilibrium? (i) (ii) (iii) The rate of the reverse reaction increases. The concentration of Il(g) increases. The concentration of l 2 (g) increases. (i) only (ii) only (i) and (iii) only (ii) and (iii) only (2) 1.10 onsider the reaction represented by the equation below: 3 PO 4 (aq) + O 3 (aq) 2 PO 4 (aq) + 2 O 3 (aq) K a > 1 The strongest base in the above reaction is: 2 PO 4 O 3 3 PO 4 2 O 3 (2) [20]

7 Physical Sciences/P2 7 E/2014 QUESTION 2 (Start on a new page.) The letters to G in the table below represent seven organic compounds. O n O O E utane F G Ethyl propanoate 2.1 Write down the: Name of the homologous series to which compound F belongs (1) Name of the functional group of compound (1) Letter that represents a primary alcohol (1) IUP name of compound (2) Structural formula of the monomer of compound (2) alanced equation, using molecular formulae, for the combustion of compound E in excess oxygen (3) 2.2 riefly explain why compounds and are classified as POSITIONL ISOMERS. (2) 2.3 ompound G is prepared using an alcohol as one of the reactants. Write down the balanced equation for the reaction using structural formulae for all the organic reagents. (7) [19]

8 Physical Sciences/P2 8 E/2014 QUESTION 3 (Start on a new page.) The table below shows the results obtained from experiments to determine the boiling point of some alkanes and alcohols of comparable molecular masses. ompound Relative oiling point molecular mass ( ) O O O O efine the term boiling point. (2) 3.2 onsider the boiling points of the four alkanes in the above table escribe the trend in their boiling points. (1) Fully explain the trend in QUESTION (3) 3.3 The boiling point of each alcohol is much higher than that of the alkane of comparable relative molecular mass. Explain this observation by referring to the type and strength of the intermolecular forces in alkanes and alcohols. (2) [8]

9 Physical Sciences/P2 9 E/2014 QUESTION 4 (Start on a new page.) The flow diagram below shows the preparation of different organic compounds using 3 = 2 as starting material. X, Y, Z and P represent different organic reactions. 3 = 2 X 3 l 3 P Z n alcohol 2 SO 4 Y n alkene 4.1 To which homologous series does 3 = 2 belong? (1) 4.2 Write down the: Type of reaction of which X is an example (1) Structural formula and IUP name of the alcohol produced during reaction P (3) Type of reaction of which Y is an example (1) Function of the acid in reaction Y (1) 4.3 For reaction Z, write down: The NME of the inorganic reagent needed (1) TWO reaction conditions needed (2) balanced equation for the production of the alkene, using structural formulae (5) [15]

10 Physical Sciences/P2 10 E/2014 QUESTION 5 (Start on a new page.) Zinc granules are added to 100 cm 3 of a 0,2 mol dm -3 hydrochloric acid solution in an Erlenmeyer flask. The equation for the reaction that takes place is: Zn(s) + 2l(aq) Znl 2 (aq) + 2 (g) 0,2 mol dm -3 hydrochloric acid solution Gas bubbles Zinc granules alance The rate of the reaction is followed by measuring the loss in mass of the flask and its contents at regular time intervals. fter completion of the reaction, it is found that 0,12 g zinc granules did not react. 5.1 Which reactant is the limiting reagent? (1) 5.2 Give a reason for the loss in mass of the flask and its contents. (1) 5.3 Sketch a graph of the mass of zinc versus time for the above reaction. Label this graph P. (2) 5.4 On the same set of axes as in QUESTION 5.3, sketch graph Q which represents the same reaction at a IGER TEMPERTURE. (1) 5.5 Use the collision theory to explain why graph Q differs from graph P. (2) 5.6 alculate the mass of zinc initially present in the flask. (6) [13]

11 Physical Sciences/P2 11 E/2014 QUESTION 6 (Start on a new page.) sample of N 2 O 4 gas is sealed in a container and heated. The N 2 O 4 gas decomposes to NO 2 gas and the reaction reaches equilibrium according to the following balanced equation: N 2 O 4 (g) 2NO 2 (g) Δ > 0 The graph below shows how the concentrations of the two gases change as a result of changes made to the reaction conditions. oncentration (mol dm -3 ) N 2 O 4 (g) NO 2 (g) 0 t 1 t 2 t 3 t 4 Time (min.) 6.1 efine the term chemical equilibrium. (2) 6.2 ow does the rate of the forward reaction compare to that of the reverse reaction at each of the following times? Only write down IGER TN, LOWER TN or EQUL TO t 1 (1) t 2 (1) 6.3 What change was made to the reaction conditions at each of the following times? In both instances, the equilibrium constant for the reaction did not change t 3 (1) t 4 (1) 6.4 ow will an increase in temperature influence the yield of NO 2 (g)? Write down INRESES, ERESES or REMINS TE SME. Use Le hatelier's principle to explain the answer. (3) 6.5 Initially 0,92 mol N 2 O 4 gas is sealed in a 2 dm 3 container and heated to 100. t equilibrium it is found that 20,7% of the N 2 O 4 gas has decomposed to NO 2 gas. alculate the equilibrium constant (K c ) for this reaction at 100. (7) [16]

12 Physical Sciences/P2 12 E/2014 QUESTION 7 (Start on a new page.) Grade 12 class wants to determine the percentage of ethanoic acid in a certain bottle of vinegar. They titrate a sample taken from the bottle of vinegar with a standard solution of sodium hydroxide. The equation for the reaction is: 3 OO(aq) + NaO(aq) 3 OONa(aq) + 2 O(l) 7.1 efine an acid in terms of the rrhenius theory. (2) 7.2 Give a reason why ethanoic acid is classified as a weak acid. (1) 7.3 Explain the meaning of standard solution. (1) 7.4 Write down the names of TWO items of apparatus needed to measure accurate volumes of the acid and the base in this titration. (2) 7.5 It is found that 40 ml of a 0,5 mol dm -3 sodium hydroxide solution is needed to neutralise 20 ml of the vinegar. alculate the: p of the sodium hydroxide solution (4) Percentage of ethanoic acid by mass present in the vinegar (ssume that 1 ml of vinegar has a mass of 1 g.) (7) 7.6 The sodium ethanoate ( 3 OONa) formed during the above neutralisation reaction undergoes hydrolysis to form an alkaline solution. Write down an equation for this hydrolysis reaction. (3) [20]

13 Physical Sciences/P2 13 E/2014 QUESTION 8 (Start on a new page.) The voltaic cell represented below functions at standard conditions. V graphite graphite I 2 (s) I - (aq) + (aq) MnO 4 (aq); Mn 2+ (aq) 8.1 Write down the concentration of + (aq) in the one half-cell. (1) 8.2 Solids present in half-cells are usually used as electrodes. Give a reason why I 2 (s) is not suitable to be used as an electrode. (1) 8.3 Write down TWO properties of graphite, other than being a solid, that makes it suitable for use as electrodes in the above voltaic cell. (2) 8.4 For the above voltaic cell, write down the: NME of the oxidising agent (1) Net cell reaction (3) ell notation (3) 8.5 alculate the cell potential of the above cell. (4) 8.6 ow will the reading on the voltmeter be affected if the concentration of MnO 4 (aq) decreases? Only write down INRESES, ERESES or NO EFFET. (1) [16]

14 Physical Sciences/P2 14 E/2014 QUESTION 9 (Start on a new page.) technician is plating a bracelet with chromium in an electrolytic cell containing r 2 (SO 4 ) 3 (aq). simplified diagram of the electrolytic cell is shown below. Power source racelet r 2 (SO 4 ) 3 (aq) Electrode X 9.1 efine the term electrolyte. (2) 9.2 Which electrode, the RELET or X, is the cathode? (1) 9.3 Write down the: Metal of which electrode X is made (1) Reduction half-reaction (2) 9.4 uring the process, the bracelet is plated with 0,86 g of chromium. alculate the number of electrons transferred during the process. (6) [12]

15 Physical Sciences/P2 15 E/2014 QUESTION 10 (Start on a new page.) Sulphuric acid is used, amongst others, in the manufacturing of fertilisers. The flow diagram below shows how fertiliser can be prepared using sulphuric acid as one of the reagents. Sulphur Oxygen ompound ompound ompound Sulphuric acid mmonia Fertiliser 10.1 Write down the NME of the industrial process for the preparation of sulphuric acid. (1) 10.2 ompound is formed when sulphur burns in oxygen. Write down the NME or FORMUL of compound. (1) 10.3 ompound is formed when compound reacts with oxygen in the presence of a catalyst. Write down the: NME or FORMUL of the catalyst (1) alanced equation for the reaction which takes place (3) 10.4 ompound is dissolved in concentrated sulphuric acid to form compound. Write down the: NME or FORMUL of compound (1) Reason why compound is not dissolved in water to form sulphuric acid (1) 10.5 Write down the NME or FORMUL of fertiliser. (1) 10.6 Inorganic fertilisers are soluble in water. This can result in eutrophication if they are washed off into rivers during heavy rain. Write down ONE negative impact of eutrophication on the economy of a country. (2) [11] TOTL: 150

16 Physical Sciences/P2 1 E/2014 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 p 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 vogadro's constant vogadro-konstante N 6,02 x mol -1 TLE 2: FORMULE/TEL 2: FORMULES m n= M n c = or/of V c ava na c V n b b b m c = MV n= n= N N V V m = p = -log[ 3 O + ] K w = [ 3 O + ][O - ] = 1 x at/by 298 K E cell = E E / E cathode anode sel = E katode E anode or/of E = E E / E cell reduction oxidation sel = E reduksie E oksidasie or/of E = E E / E cell oxidising agent reducing agent sel = E oksideermiddel E reduseermiddel

17 2,1 1,0 0,9 0,8 0,8 0,7 0,7 1 (I) Physical Sciences/P2 2 E/ Li 7 11 Na K Rb s Fr 1,5 1,2 1,0 1,0 0,9 0,9 2 (II) 4 e 9 12 Mg a Sr a Ra 226 1,3 1,2 TLE 3: TE PERIOI TLE OF ELEMENTS TEL 3: IE PERIOIEKE TEL VN ELEMENTE (III) tomic number KEY/SLEUTEL toomgetal 21 Sc Y La 139 1,5 1,4 1,6 22 Ti Zr f 179 1,6 23 V Nb Ta c 58 e 140 Electronegativity Elektronegatiwiteit 90 Th 232 1,6 1,8 24 r Mo W Pr Pa 1,5 1,9 25 Mn Tc 75 Re Nd U 238 1,9 1,8 2,2 29 u 63,5 26 Fe Ru Os Pm 93 Np 1,8 2,2 27 o Rh Ir Sm Pu Symbol Simbool pproximate relative atomic mass enaderde relatiewe atoommassa 1,8 2,2 28 Ni Pd Pt Eu m 1,9 1,9 29 u 63,5 47 g u Gd m 1,6 1,7 30 Zn d g Tb k 2,0 1,5 1,6 1,7 1, l Ga In Tl y f 2,5 1,8 1,8 1,8 1,8 14 (IV) Si Ge Sn Pb o Es 3,0 2,1 2,0 1,9 1,9 15 (V) 7 N P s Sb i Er Fm 3,5 2,5 2,4 2,1 2,0 16 (VI) 8 O S Se Te Po 69 Tm Md 4,0 3,0 2,8 2,5 2,5 17 (VII) 9 F l 35,5 35 r I t 70 Yb No 18 (VIII) 2 e 4 10 Ne r Kr Xe Rn 71 Lu Lr

18 Physical Sciences/P2 3 E/2014 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 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 Increasing reducing ability/toenemende reduserende vermoë

19 E Physical Sciences/P2 4 E/2014 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 0,91 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 Increasing oxidising ability/toenemende oksiderende vermoë 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 Increasing reducing ability/toenemende reduserende vermoë