Physical Sciences Grade 12 IEB Paper 2 2018 Question Paper

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE EXAMINATION NOVEMBER 2018 PHYSICAL SCIENCES: PAPER II Time: 3 hours 200 marks PLEASE READ THE FOLLOWING INSTRUCTIONS CAREFULLY 1. This question paper consists of 18 pages, a yellow ANSWER SHEET of 2 pages (i–ii) and a green DATA SHEET of 3 pages (i–iii). Please check that your question paper is complete. 2. Remove the DATA SHEET and ANSWER SHEET from the middle of this question paper. Write your examination number on the yellow ANSWER SHEET. 3. Read the questions carefully. 4. Answer ALL the questions. 5. Question 1 consists of 10 multiple-choice questions. There is only one correct answer to each question. The questions are to be answered on the answer sheet provided on the inside cover on your answer book. The letter that corresponds with your choice of the correct answer must be marked with a cross as shown in the example below. A B C D Here the answer C has been marked. 6. START EACH QUESTION ON A NEW PAGE. 7. Please ensure that you number your answers as the questions are numbered. 8. Unless instructed otherwise it is NOT necessary to give state symbols (phase indicators) when asked to write a balanced chemical equation. 9. Use the data and formulae whenever necessary. 10. Show all the necessary steps in calculations. 11. Where appropriate, take your answers to 2 decimal places. 12. It is in your interest to write legibly and to present your work neatly. IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 2 of 18 QUESTION 1 MULTIPLE CHOICE Answer these questions on the multiple-choice answer sheet on the inside front cover of your Answer Book. Make a cross (X) in the box corresponding to the letter that you consider to be most correct. 1.1 The chemical formula for dinitrogen tetroxide is: A NO B N2O4 C N4O2 D N2O5 1.2 An exothermic reaction is one in which: A there is an increase in temperature of the reaction mixture. B there is a conversion from thermal energy into potential energy. C there is a low activation energy. D there is a high number of effective collisions per second. 1.3 A container is filled with H2 and Br2 gases and sealed at a particular temperature. The gases react as shown in the following balanced chemical equation: H2(g) + Br2(g) ⇌ 2HBr(g) ΔH < 0 The changes in the amounts of H2 and HBr are shown by the solid lines in the graph below. H2 H2 Amount (mol) HBr HBr Time The reaction is then repeated under different conditions. Which one of the following changes to the original conditions would result in the dashed lines (- - - -) shown on the graph? A A higher pressure B A higher temperature C A higher concentration of Br2 D Addition of a suitable catalyst IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 3 of 18 1.4 The average rate of formation of CO2 in the following reaction is 0,5 mol·min−1. CaCO3(s) + 2HCℓ(aq)  CaCℓ2(aq) + CO2(g) + H2O(ℓ) The average rate of consumption (disappearance) of HCℓ for this same reaction is: A 0,25 mol·min−1 B 0,5 mol·min−1 C 1 mol·min−1 D 2 mol·min−1 1.5 Which one of the following will behave as a weak, polyprotic acid when dissolved in water? A NH3 B HNO2 C H2SO3 D (NH4)2SO4 1.6 Water is added to a 0,01 mol·dm−3 solution of nitric acid. Which one of the following describes the change in concentration of hydronium ions and pH in this solution as water is added? [H3O+] pH A Remains the same Remains the same B Increases Decreases C Increases Increases D Decreases Increases 1.7 A small amount of a salt with the formula XZ is dissolved in distilled water at 25 °C. The Kb value for XOH is 3,2 × 106 at 25 °C and the Ka value for HZ is 1,6 × 10−5 at 25 °C. What is the approximate pH of the solution of XZ at 25 °C? A 5 B 7 C 9 D 14 1.8 A galvanic cell is constructed under standard conditions. The spontaneous reaction that occurs is represented by the following balanced chemical equation: 2Aℓ + 3Co2+  2Aℓ3+ + 3Co Which one of the following is the standard potential for this cell? A +1,38 V B −1,38 V C +2,48 V D −2,48 V IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 4 of 18 1.9 The process used to deposit a metal onto a conductive object is called: A Electrolysis B Electrorefining C Electroextraction D Electroplating 1.10 Which one of the following is NOT a property of carbon that enables it to be the building block of organic chemistry? A It forms strong covalent bonds to other atoms. B It forms weak induced dipole forces with other atoms. C It has a valency of four in a tetrahedral arrangement. D It can form bonds to itself. [20] IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 5 of 18 THIS PAGE HAS DELIBERATELY BEEN LEFT BLANK IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 6 of 18 QUESTION 2 Chromium metal reacts with hydrochloric acid to produce a green solution of chromium(III) chloride and hydrogen gas, as shown in the following balanced chemical equation. 2Cr(s) + 6HCℓ(aq) → 2CrCℓ3(aq) + 3H2(g) ΔH < 0 2.1 A partially drawn potential energy profile for this reaction is provided on your ANSWER SHEET. 2.1.1 Complete this energy profile. (1) 2.1.2 Write the relevant labels in the boxes provided. (3) Dana performs a series of experiments to test the effect of certain factors on the average rate of reaction between chromium metal and hydrochloric acid. In each of the experiments, Dana ensures that chromium is the limiting reagent and is always completely covered by the same volume of hydrochloric acid of the same concentration. The reaction conditions for each of the experiments are tabulated below. Experiment State of Mass of Temperature (°C) chromium chromium (g) 1 Single lump 6,0 25 2 Single lump 6,0 15 3 Fine powder 4,5 25 Dana observes that in all three experiments, all of the chromium fully reacts in less than 80 s. Dana collects the hydrogen gas produced at STP at set time intervals. Dana's results for experiment 1 are shown on the graph below. 4,5 Volume of H2 gas (dm3) 3,0 1,5 0 0 20 40 60 80 Time (s) IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 7 of 18 2.2 Dana's graph has been reproduced on your ANSWER SHEET. On the axes provided, redraw the graph that would result for: 2.2.1 Experiment 2 (2) 2.2.2 Experiment 3 (3) 2.3 Other than measuring the volume of collected hydrogen gas produced over time, briefly describe ONE alternative method that could have been used to measure the rate of this reaction. In your answer, specify what equipment should be used and what measurements should be made. (3) 2.4 Consider the reaction conditions and the graph given for Experiment 1. 2.4.1 Determine the total amount (in moles) of hydrogen gas collected at STP. Round your answer to 3 decimal places. (3) 2.4.2 Considering that the chromium metal is the limiting reagent, calculate the percentage yield of hydrogen gas in this reaction. (5) 2.4.3 Calculate the average rate of formation of H2 (during the first 40 s) in units of dm3·s−1. Round your answer to 3 decimal places. (2) 2.5 According to the collision theory, when reacting particles collide, not all of these collisions result in a reaction occurring, i.e. not all of these collisions are effective. State TWO conditions necessary for an effective collision. (2) 2.6 Explain fully, in terms of the collision theory, how the reaction rate would be affected if a higher concentration of HCℓ were used. (4) 2.7 Consider pure hydrogen chloride, HCℓ(g). 2.7.1 Define covalent bond. (2) 2.7.2 Define electronegativity. (2) 2.7.3 With reference to the difference in electronegativity between hydrogen and chlorine, explain why the covalent bond in hydrogen chloride is considered to be polar. (3) [35] IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 8 of 18 QUESTION 3 The reaction represented by the following balanced chemical equation is important in the Contact Process for the industrial production of sulfuric acid: 2SO2(g) + O2(g) ⇌ 2SO3(g) Dikeledi adds some sulfur dioxide and oxygen to a container and then seals the container. He monitors the rates of the forward and reverse reactions over time and the following graph is obtained: Reaction Rate 0 5 10 15 20 Time (min) 3.1 After what time was dynamic equilibrium reached for the first time? (1) 3.2 Write down the equation for the reaction represented by the solid line. (2) 3.3 State Le Châtelier's principle. (2) 3.4 At 8 minutes, more oxygen gas was added to the container whilst maintaining a constant temperature and volume of container. With reference to Le Châtelier's principle, fully explain how the amount of sulfur dioxide was affected when the equilibrium was re-established. (3) 3.5 At 15 minutes, the temperature of the reaction mixture was suddenly decreased. 3.5.1 From the graph, determine and write down which reaction (FORWARD or REVERSE) was initially favoured. (1) 3.5.2 Is the forward reaction EXOTHERMIC or ENDOTHERMIC? No explanation is necessary. (2) IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 9 of 18 3.6 The following equations may be used to represent the rates of the forward and the reverse reaction: Rate of forward reaction = k1[SO2]2[O2] Rate of reverse reaction = k2[SO3]2 where k1 and k2 are constants. If the pressure of the system is decreased by increasing the volume of the container, both the forward and reverse reaction rates will decrease, but the forward rate will decrease more than the reverse. 3.6.1 Consider the rate equations provided and state why a decrease in pressure causes both reaction rates to decrease. (1) 3.6.2 With reference to the rate equations provided, explain why a decrease in pressure causes the forward reaction rate to decrease more than the reverse. (2) [14] IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 10 of 18 QUESTION 4 The balanced chemical equation below shows a hydrated copper(II) ion, which is blue in colour, reacting with chloride ions to form the complex copper tetrachloride ion, which is green in colour. An aqueous equilibrium mixture is prepared in order to obtain a mixture that is initially blue-green in colour at 25 °C. − 2– Cu(H2 O)2+ 6 (aq) + 4Cℓ (aq) ⇌ CuCℓ 4 (aq) + 6H2O(ℓ) ΔH > 0 BLUE GREEN 4.1 What would happen to the equilibrium concentration of Cℓ− ions if the reaction mixture were cooled? State only INCREASES, DECREASES or REMAINS THE SAME. (2) 2– 4.2 Which reaction will be favoured by the addition of CuCℓ 4 ions to the reaction mixture? State only FORWARD or REVERSE. (2) 4.3 What would happen to the colour of the mixture if crystals of sodium chloride were dissolved in the reaction mixture? State only TURNS BLUE, TURNS GREEN or REMAINS THE SAME. (2) 2– 4.4 A new solution is prepared by dissolving 4 mol of CuCℓ 4 completely in water to make up a solution of volume 2 dm3. When equilibrium is established, there are 2,2 mol of Cu(H2 O)2+ 6 ions present at 25 °C. − 2– Cu(H2 O)2+ 6 (aq) + 4Cℓ (aq) ⇌ CuCℓ 4 (aq) + 6H2O(ℓ) 4.4.1 Write an expression for the equilibrium constant for this reaction. (2) 4.4.2 Determine the value of the equilibrium constant, Kc, for this reaction at 25 °C. (6) [14] IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 11 of 18 QUESTION 5 Consider sodium hydroxide (NaOH), a strong base, and butanoic acid, a weak organic acid with the molecular formula C4H8O2. 5.1 Define a base in terms of the Lowry-Brønsted model. (1) 5.2 Why is NaOH considered to be a strong base? (2) 5.3 Write down the formula of another strong base. (1) 5.4 Write a reaction equation for the dissociation of NaOH in water. (2) 5.5 Consider aqueous solutions of NaOH and butanoic acid of equal concentrations. Which solution will have a greater conductivity? FULLY explain the answer. (4) 5.6 Draw the structural formula of butanoic acid. (2) 5.7 Give the IUPAC name of a FUNCTIONAL isomer of butanoic acid. (2) [14] IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 12 of 18 QUESTION 6 Latif performs a titration by slowly adding a dilute standard solution of NaOH by burette to an unknown volume of a standard solution of butanoic acid that has been placed in an Erlenmeyer flask. A simplified diagram of this experimental setup is shown below. Burette containing NaOH Erlenmeyer flask with acid White tile Latif monitors the concentration of hydronium ions as the base is added to the flask, and he arrives at the table of selected results below: [H3O+] in flask Volume of NaOH added (mol·dm−3) (cm3) 1 × 10−3 0 6,31 × 10−5 10 3,16 × 10−9 30 1 × 10−12 50 6.1 How does the pH of the solution in the flask change on addition of NaOH? State only INCREASES, DECREASES, or REMAINS THE SAME. (1) 6.2 Calculate the concentration of hydroxide ions in the solution after the addition of 10 cm3 of NaOH at 25 °C. (4) IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 13 of 18 6.3 The concentration of the butanoic acid solution used was 0,21 mol·dm−3, and the neutralisation point was reached after the addition of 0,0165 mol of NaOH. The neutralisation reaction is represented by the balanced chemical equation below. NaOH(aq) + C3H7COOH(aq) → C3H7COONa(aq) + H2O(ℓ) 6.3.1 Define the term neutralisation or equivalence point. (2) 6.3.2 Determine the number of moles of butanoic acid that was neutralised. Use 4 decimal places in your answer. (1) 6.3.3 Calculate the original volume (in cm3) of the butanoic acid solution that was placed in the flask. (4) 6.4 At the neutralisation point, the solution in the flask is basic. This is due to the following hydrolysis reaction: C3H7COO−(aq) + H2O(ℓ) ⇌ C3H7COOH(aq) + OH−(aq) 6.4.1 Define the term hydrolysis. (2) 6.4.2 With reference to this hydrolysis equation, explain why the solution in the flask is basic at the neutralisation point. (2) 6.5 Latif states: "Because NaOH is a strong base, a solution of NaOH will ALWAYS have a higher pH than a solution of a weak base such as NH3." Evaluate Latif's statement. (3) [19] IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 14 of 18 QUESTION 7 A galvanic cell is constructed using a standard Cℓ2|Cℓ− half-cell and a standard Ni|Ni2+ half-cell, as shown in the diagram below. The solution in the nickel half-cell is initially pale green. V Ni(s) Cℓ2 (g) Pt(s) HCℓ(aq) Ni(NO3)2(aq) 7.1 The reduction half-reaction that occurs in this cell is shown below: Cℓ2 + 2e− → 2Cℓ− 7.1.1 Define oxidising agent. (1) 7.1.2 With reference to the strengths of oxidising agents, explain why Cℓ2 is reduced instead of Ni2+. (2) 7.2 7.2.1 Define anode. (2) 7.2.2 Identify the anode in this cell. (1) 7.3 Identify the positive electrode in this cell. (1) 7.4 Write the cell notation for this cell, including relevant conditions. State symbols need not be shown. (5) 7.5 The voltmeter is now replaced with a light bulb so that current flows. 7.5.1 Write down the half-reaction that occurs in the nickel half-cell. (2) 7.5.2 Hence, state TWO changes that will be observed in the nickel half- cell after a significant amount of time has passed. (2) 7.5.3 One of the functions of the salt bridge is to maintain electrical neutrality. State ONE other function of the salt bridge. (1) 7.5.4 Explain how the salt bridge maintains electrical neutrality with reference to the changing ionic conditions in the nickel half-cell. (2) 7.6 Lerusha accidentally drops some concentrated AgNO3 solution into the chlorine half-cell, causing a white precipitate of AgCℓ to form. How would this affect the initial cell emf? State only INCREASES, DECREASES or REMAINS THE SAME. (2) [21] IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 15 of 18 QUESTION 8 Aluminium is produced in modern times through the Hall-Héroult process, whereby a molten aluminium oxide electrolyte is electrolysed between graphite electrodes. A simplified diagram of the cell used in the Hall-Héroult process is shown below. Graphite ANODES Steel container lined with graphite Aluminium oxide (CATHODE) and Cryolite Aℓ(ℓ) Although the production of aluminium is expensive, it is worth the cost. Aluminium is light, so it is useful in the manufacture of aircrafts and cars. It protects itself from corrosion by producing a layer of aluminium oxide on its surface, which is very tough and therefore difficult to remove. 8.1 From the information given above, write down ONE physical property of aluminium that makes it a useful metal. (1) 8.2 From the information given above, write down ONE chemical property of aluminium that makes it a useful metal. (1) 8.3 Identify the positive electrode in the above cell. State only ANODE or CATHODE. (1) 8.4 Write down the ionic equation for the half-reaction that occurs at the cathode. (2) 8.5 Explain briefly how the use of cryolite to decrease the melting point of the electrolyte is: 8.5.1 economically beneficial. (2) 8.5.2 environmentally harmful. (2) IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 16 of 18 8.6 Explain why the carbon anodes need regular replacing. Give a relevant chemical reaction equation to support your answer. (4) 8.7 One of the reasons aluminium is so difficult to electrolyse is that aluminium oxide has a very high melting point. With reference to the forces holding its particles together, explain why aluminium oxide has such a high melting point. (4) 8.8 Aluminium can also be produced on a small scale by the reduction of aluminium chloride by sodium metal, shown in the UNBALANCED chemical equation below. AℓCℓ3 + Na → Aℓ + NaCℓ 8.8.1 Balance the above equation. (2) 8.8.2 A chemical engineer wants to test what mass of sodium metal is needed to react completely in order to make 7,56 mol of pure aluminium metal, using this reaction. Calculate the mass of sodium metal needed to do this. (3) [22] IEB Copyright © 2018

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 17 of 18 QUESTION 9 Consider the compounds, labelled A, B, and C, below and answer the questions that follow. H H C H H H Br H H H H H H C C C C C H H C C C C C C H pentan−2−ol H H H H H H H H C H H C H H C H H H A B C 9.1 9.1.1 Write down the IUPAC name for compound A. (4) 9.1.2 Draw the condensed-structural formula for compound A. (2) 9.2 9.2.1 NAME the homologous series to which compound B belongs. (1) 9.2.2 Draw the structural formula for the unbranched CHAIN isomer of compound B. (2) 9.3 9.3.1 NAME the functional group present in compound C. (1) 9.3.2 State what is meant by the term positional isomers. (2) 9.3.3 Draw the structural formula for a POSITIONAL isomer of compound C. (2) 9.4 9.4.1 Define intermolecular force. (2) 9.4.2 Compound C has a significantly higher viscosity than compound B. Account for this difference with reference to the relevant intermolecular forces in each of these compounds. (4) 9.5 Using molecular formulae, write a balanced chemical equation for the complete combustion of compound B. (4) [24] IEB Copyright © 2018 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: PHYSICAL SCIENCES: PAPER II Page 18 of 18 QUESTION 10 Consider the flow chart below showing the interconversion of organic molecules through organic reactions, and answer the questions that follow. W to Z are organic compounds, and 1 to 7 are organic reactions. W pentyl ethanoate 7 1 Z 6 H H H H H 4 5 H C C C C C H 2 Cl H H H H CH2CHCH2CH2CH3 X Y 3 The conditions for reactions 1, 5 and 7 are tabulated below. Reaction Conditions 1 Cℓ2 gas is bubbled through compound W in the presence of UV light. 5 Compound Y is treated with steam and H3PO4(aq). Compound Z is heated gently with a carboxylic acid, together with a 7 few drops of concentrated H2SO4(aq). 10.1 Define hydrocarbon. (2) 10.2 Write down the IUPAC name for hydrocarbon W. (2) 10.3 Identify the general TYPE of reaction for each of the following: 10.3.1 Reaction 1 (1) 10.3.2 Reaction 5 (1) 10.3.3 Reaction 7 (1) 10.4 NAME the specific type of addition reaction represented by reaction 3. (1) 10.5 Write down the IUPAC name of compound Y. (2) 10.6 Classify compound Y as SATURATED or UNSATURATED. (1) 10.7 Consider reactions 5, 6 and 7 and write down the IUPAC NAME of compound Z. (3) 10.8 Draw the structural formula of pentyl ethanoate. (2) 10.9 Write down the NUMBER of the reaction that would take place if the relevant organic compound were heated strongly in the presence of concentrated alcoholic potassium hydroxide. (1) [17] Total: 200 marks IEB Copyright © 2018