NATIONAL SENIOR CERTIFICATE GRADE 11

Transcription

1 NTIONL SENIOR ERTIFITE GRE 11 PHYSIL SIENES: HEMISTRY (P2) NOVEMER 2017 MRKS: 150 TIME: 3 hours This question paper consists of 11 pages, 4 data sheets and 1 answer sheet.

2 Physical Sciences/P2 2 E/November 2017 INSTRUTIONS N INFORMTION Write your name and class (for example 11) in the appropriate spaces on the NSWER OOK. This question paper consists of TEN questions. nswer LL the questions in the NSWER OOK, except QUESTION 4.1, which must be answered on the attached NSWER SHEET. Hand in the NSWER SHEET together with the NSWER OOK. Start EH 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 SHEETS. 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/November 2017 QUESTION 1: MULTIPLE-HOIE QUESTIONS Various options are provided as possible answers to the following questions. Each question has only ONE correct answer. hoose the answer and write only the letter ( ) next to the question number ( ) in the NSWER OOK, for example 1.11 E. 1.1 Which ONE of the bonds between the atoms below has the highest polarity? H - H - l H - O H - N (2) 1.2 Solid iodine sublimes easily. The intermolecular forces present in iodine are London forces. hydrogen bonding. ion-dipole forces. dipole-dipole forces. (2) 1.3 The graph below shows how the potential energy varies with distance between the nuclei of two nitrogen atoms when a double bond between the nitrogen atoms (N = N) is formed. Potential energy (kj mol -1 ) L l l l l istance between nuclei (pm) hoose from the table the bond length and bond energy for N = N. ON LENGTH (pm) ON ENERGY (kj mol -1 ) (2)

4 Physical Sciences/P2 4 E/November ccording to oyle's law, p α V 1 if T is constant. V α T if p is constant. V α T 1 if p is constant. p α V if n is constant. (2) 1.5 One mole of any gas occupies the same volume at the same temperature and pressure. This statement is known as harles's law. Gay Lussac's law. vogadro's law. the ideal gas LW. (2) 1.6 One mole of a gas, SELE in a container, has volume V at temperature T and pressure p. If the pressure is increased to 3p, the ratio between the volume and temperature (V : T) is 1 : ⅓ 3 : 1 ⅓ : 3 1 : The chemical equation that represents an endothermic reaction: NH 4 NO 3 (s) + H 2 O(l) NH + 4 (aq) + NO - 3 (aq) H > 0 2Mg(s) + O 2 (g) 2MgO(s) H < 0 Zn(s) + 2Hl(aq) Znl 2 (aq) + H 2 (g) + heat H 2 (g) + l 2 (g) 2Hl(g) H = -131 kj mol -1 (2)

5 Physical Sciences/P2 5 E/November The ORRET formula for nitric acid: H 2 SO 4 H 3 OOH NH 3 HNO 3 (2) 1.9 onsider the reaction below. Zn(s) + uso 4 (aq) ZnSO 4 (aq) + u(s) Which substance is the oxidising agent? Zn u 2+ Zn 2+ u (2) 1.10 Which ONE of the reactions below will produce the salt sodium ethanoate (sodium acetate)? Hl(s) + H 3 OOH(aq) H 3 OOH(aq) + H 2 O(l) H 3 OOH(aq) + NaOH(aq) H 2 O 3 (aq) + NaOH(aq) (2) [20]

6 Physical Sciences/P2 6 E/November 2017 QUESTION 2 (Start on a new page.) onsider the following two reactions of methane (H 4 ): Reaction 1: Reaction 2: H 4 (g) + Hl (g) H 3 l (g) + H 2 (g) H 4 (g) + 2O 2 (g) O 2 (g) + 2H 2 O (g) 2.1 efine the term covalent bond. (2) 2.2 raw Lewis structures for: H 3 l (2) O 2 (2) 2.3 How many lone-pair electrons are on the central atom in the O 2 molecule? (1) 2.4 Identify ONE of the substances in Reaction 2 that can form a dative covalent bond when reacting with an acid. (1) 2.5 Write down the shape of the: H 2 O molecule (1) O 2 molecule (1) 2.6 lthough the molecules of H 4 and H 3 l have the same shape, H 4 is non-polar, while H 3 l is polar. Give a reason for the difference in molecular polarity. (1) [11] QUESTION 3 (Start on a new page.) onsider the list of six substances with their formulae and boiling points in the table below. NME OF SUSTNE FORMUL OILING POINT ( ) Water H 2 O 100 Ethanol H 3 H 2 OH 78 romine r 2 58,8 Iodine I 2 184,3 mmonia NH 3-33,3 Phosphine PH 3-87,7 3.1 Explain why ethanol is soluble in water. Refer to the relative strength of the intermolecular forces in ethanol and water. (3) 3.2 Explain why the boiling point of iodine is higher than that of bromine. Refer to the intermolecular forces present in EH substance in the explanation. (3)

7 Physical Sciences/P2 7 E/November Explain why phosphine will evaporate faster than ammonia by referring to the types of intermolecular forces present in EH substance. (4) 3.4 Water, ethanol and bromine are all liquids at room temperature. Which ONE will have the highest vapour pressure? (1) 3.5 Give a reason for the answer to QUESTION 3.4 by referring to the relative strength of the intermolecular forces and boiling points. (2) [13] QUESTION 4 (Start on a new page.) In an experiment to investigate the relationship between pressure and temperature of an enclosed gas, 48 g of oxygen gas was sealed in a container. The results obtained are recorded in the table below. PRESSURE (kpa) TEMPERTURE (K) 155, , , , , raw a graph of pressure versus temperature on the attached NSWER SHEET. Extrapolate the graph so that it intersects the y-axis. (4) 4.2 What conclusion can be made from the final graph? (2) 4.3 Explain why it will not be possible to obtain accurate values at very low temperatures. (2) 4.4 Use the kinetic molecular theory to explain the effect of an increase in temperature on the pressure of a gas. (4) 4.5 Under which conditions of temperature and pressure will a real gas act as an ideal gas? (2) 4.6 alculate the gradient of the graph. (3) 4.7 Use the answer to QUESTION 4.6 to determine the volume of the container. (5) [22]

8 Physical Sciences/P2 8 E/November 2017 QUESTION 5 (Start on a new page.) Weather balloons are sent into space to gather data. The balloons usually burst at a pressure of Pa and a volume of 36,3 m 3. The data collector then falls back to Earth. balloon The gas in a certain weather balloon has an initial volume of 12,6 m 3 and pressure of Pa at a temperature of 25 when it is released into space. alculate the: 5.1 Temperature of the gas, in, in the balloon when it bursts (4) 5.2 Initial amount of gas (in moles) in the balloon (4) [8] QUESTION 6 (Start on a new page.) data collector 6.1 The decomposition of hydrogen peroxide in the presence of a catalyst at standard pressure and room temperature is given by the unbalanced chemical equation below. H 2 O 2 (aq) H 2 O(l) + O 2 (g) The oxygen gas is collected and the volume is recorded over a period of time. The reaction is completed at time t. The results are plotted on a graph of volume O 2 versus time, as shown below. Volume O2 (cm 3 ) 600 t Time (s) Take the molar gas volume (V m ) as 24,45 dm 3 standard pressure. at room temperature and alance the equation. (2) How would a catalyst affect the reaction? (2) Use the information on the graph to calculate the mass of hydrogen peroxide that decomposed. (6)

9 Physical Sciences/P2 9 E/November In an experiment, a learner adds 500 cm 3 hydrochloric acid (Hl), with a concentration of 0,36 mol dm -3, to 1,2 g of magnesium in a test tube. She records the change in the mass of magnesium as the reaction proceeds at regular intervals. The balanced chemical equation for the reaction is: Mg(s) + 2Hl(aq) Mgl 2 (aq) + H 2 (g) The change in the mass of magnesium during the reaction is shown on the graph below. 1,2 Magnesium (g) Time (min.) Identify the limiting agent in this reaction. Give a reason for the answer. (2) alculate the number of moles of unreacted hydrochloric acid in the test tube after 3 minutes. (7) [19] QUESTION 7 (Start on a new page.) The equation for the combustion of butane gas is given below. butane(g) + 13O 2 (g) 8O 2 (g) + 10H 2 O(g) H < efine the term activation energy. (2) 7.2 Is the combustion reaction of butane exothermic or endothermic? Give a reason for the answer. (2) 7.3 raw a sketch graph of potential energy versus course of reaction for the reaction above. learly indicate the following on the graph: ctivation energy Heat of reaction ( H) Reactants and products (3) 7.4 etermine the empirical formula of butane gas if it consists of 82,76% carbon and 17,24% hydrogen. (4) [11]

10 Physical Sciences/P2 10 E/November 2017 QUESTION 8 (Start on a new page.) 8.1 Two reactions of sulphuric acid are shown in the diagram below. H 2 SO 4 Reaction 1 NaOH Salt X + Product Y Reaction 2 H2O mpholyte + H 3 O efine a Lowry-rønsted base. (2) Write down a balanced equation for Reaction 1. (3) Write down the NME of the salt represented by X. (2) Write down the FORMUL of ampholyte. (2) Write down the formulae of the TWO conjugate acid-base pairs in Reaction 2. (4) 8.2 solution of sodium hydroxide (NaOH) is prepared by dissolving 6 g solid NaOH in 500 cm 3 water. This solution reacts completely with 10 g impure ammonium chloride (NH 4 l) according to the equation below. NaOH(aq) + NH 4 l(s) Nal(aq) + H 2 O(l) + NH 3 (aq) alculate the concentration of the NaOH solution. (4) alculate the percentage impurities in the NH 4 l. (6) [23] QUESTION 9 (Start on a new page.) The reaction between dichromate ions (r 2 O 7-2 ) and iron(ii) ions (Fe 2+ ) in an acidic medium is given below. r 2 O 7-2 (aq) + Fe 2+ (aq) + H + (aq) r 3+ (aq) + Fe 3+ (aq) + H 2 O(l) 9.1 etermine the oxidation number of HROMIUM in r 2 O 7-2 (aq). (2) 9.2 efine reduction in terms of electron transfer. (2) 9.3 Write down the FORMUL of the substance that undergoes oxidation. Explain the answer in terms of oxidation numbers. (2)

11 Physical Sciences/P2 11 E/November Write down the FORMUL of the oxidising agent. (2) 9.5 Write down the reduction half-reaction. (2) 9.6 Write down the net balanced ionic equation for the reaction, using the ion-electron method. (3) [13] QUESTION 10 (Start on a new page.) Gold and iron are two of many minerals mined in South frica. Iron is mined in open-cast mines, while gold is usually found in deep-shaft (underground) mines. uring the process of refining, the following chemical reactions take place to extract the metal from the ore: Gold is dissolved in a solution containing cyanide ions (N - ) to extract it from the ore. The balanced chemical equation for the reaction is: 4u(s) + 8NaN(aq) + 2H 2 O(l) + O 2 (g) 4Nau(N) 2 (aq) + NaOH(aq) Iron(Vl) oxide and carbon are heated in a furnace to extract iron from the ore. The balanced chemical equation for the reaction is: 2Fe 2 O 3 (s) +3(s) 4Fe(l) + 3O 2 (g) 10.1 State TWO advantages of open-cast mining when compared to deep-shaft (underground) mining. (2) onsider the iron extraction reaction Is iron oxidised or reduced during the reaction? Give a reason for the answer. (2) 10.3 State TWO disadvantages of using carbon in this reaction. (2) onsider the gold extraction reaction Give ONE reason why gold is present as an element in the ore. (2) 10.5 What role does oxygen gas (O 2 ) play in the reaction? (2) [10] TOTL: 150

12 Physical Sciences/P2 1 E/November 2017 T FOR PHYSIL SIENES GRE 11 PPER 2 (HEMISTRY) GEGEWENS VIR FISIESE WETENSKPPE GR 11 VRESTEL 2 (HEMIE) TLE 1: PHYSIL ONSTNTS/TEL 1: FISIESE KONSTNTES NME/NM SYMOL/SIMOOL VLUE/WRE vogadro's constant vogadro-konstante N 6,02 x mol -1 Molar gas constant Molêre gaskonstante R 8,31 J K -1 mol -1 Standard pressure Standaarddruk θ 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 θ T 273 K TLE 2: FORMULE/TEL 2: FORMULES p V p V = pv = nrt T1 T2 m n= M V n= V m n= N N n c = OR/OF V m c = MV

13 Physical Sciences/P2 2 E/November ,1 1,0 0,9 0,8 0,8 0,7 0,7 1 (I) 1 H 1 3 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 TLE 3: THE PERIOI TLE OF ELEMENTS/TEL 3: IE PERIOIEKE TEL VN ELEMENTE 1,3 1, (III) 21 Sc Y La 139 1,5 1,4 1,6 22 Ti Zr Hf 179 1,6 23 V Nb Ta c 58 e 140 KEY/SLEUTEL Electronegativity Elektronegatiwiteit 90 Th 232 enaderde relatiewe atoommassa 24 r Mn Fe o ,6 Mo W Pr Pa 1,5 1,9 43 Tc 75 Re Nd U 238 tomic number toomgetal 1,9 2,2 29 u 63,5 44 Ru Os Pm 93 Np 2,2 Rh Ir Sm Pu Symbol Simbool pproximate relative atomic mass 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 Hg Tb k 2,0 1,5 1,6 1, l Ga In Tl y f 2,5 14 (IV) Si Ge Sn Pb Ho 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 He 4 10 Ne r Kr Xe Rn 71 Lu Lr

14 Physical Sciences/P2 3 E/November 2017 Increasing oxidising ability/toenemende oksiderende vermoë θe TLE 4: STNR REUTION POTENTILS TEL 4: STNR-REUKSIEPOTENSILE Half-reactions/Halfreaksies (V) F 2(g) + 2e 2F + 2,87 o 3+ + e o H 2O 2 + 2H + +2e 2H 2O +1,77 MnO 4 + 8H+ + 5e Mn H 2O + 1,51 l 2(g) + 2e 2l + 1,36 r 2O H+ + 6e 2r H 2O + 1,33 O 2(g) + 4H + + 4e 2H 2O + 1,23 MnO 2 + 4H + + 2e Mn H 2O + 1,23 Pt e Pt + 1,20 r 2(l) + 2e 2r + 1,07 NO 3 + 4H+ + 3e NO(g) + 2H 2O + 0,96 Hg e Hg(l) + 0,85 g + + e g + 0,80 NO 3 + 2H+ + e NO 2(g) + H 2O + 0,80 Fe 3+ + e Fe ,77 O 2(g) + 2H + + 2e H 2O 2 + 0,68 I 2 + 2e 2I + 0,54 u + + e u + 0,52 SO 2 + 4H + + 4e S + 2H 2O + 0,45 2H 2O + O 2 + 4e 4OH + 0,40 u e u + 0,34 SO 4 + 4H+ + 2e SO 2(g) + 2H 2O + 0,17 u 2+ + e u + + 0,16 Sn e Sn ,15 S + 2H + + 2e H 2S(g) + 0,14 2H + + 2e H 2(g) 0,00 Fe e Fe 0,06 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 2H 2O + 2e H 2(g) + 2OH 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

15 Physical Sciences/P2 4 E/November 2017 TLE 4: STNR REUTION POTENTILS TEL 4: STNR-REUKSIEPOTENSILE Increasing oxidising ability/toenemende oksiderende vermoë 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 2H 2O + 2e H 2(g) + 2OH 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 0,06 2H + + 2e H 2(g) 0,00 S + 2H + + 2e H 2S(g) + 0,14 Sn e Sn ,15 u 2+ + e u + + 0,16 SO 4 + 4H+ + 2e SO 2(g) + 2H 2O + 0,17 u e u + 0,34 2H 2O + O 2 + 4e 4OH + 0,40 SO 2 + 4H + + 4e S + 2H 2O + 0,45 u + + e u + 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 + 0,80 g + + e g + 0,80 Hg e Hg(l) + 0,85 NO 3 + 4H+ + 3e NO(g) + 2H 2O + 0,96 r 2(l) + 2e 2r + 1,07 Pt e Pt + 1,20 MnO 2 + 4H + + 2e Mn H 2O + 1,23 O 2(g) + 4H + + 4e 2H 2O + 1,23 r 2O H+ + 6e 2r H 2O + 1,33 l 2(g) + 2e 2l + 1,36 MnO 4 + 8H+ + 5e Mn H 2O + 1,51 H 2O 2 + 2H + +2 e 2H 2O +1,77 o 3+ + e o F 2(g) + 2e 2F + 2,87 Increasing reducing ability/toenemende reduserende vermoë

16 Physical Sciences/P2 E/November 2017 NSWER SHEET Hand in this NSWER SHEET together with the NSWER OOK. NME: GRPH OF PRESSURE VERSUS TEMPERTURE Pressure (kpa) QUESTION 4.1 LSS: Temperature (K)