ATAR Chemistry Past Paper 2019 PDF

ATAR course examination, 2019 Question/Answer booklet CHEMISTRY Place one of your candidate identification labels in this box....

ATAR course examination, 2019 Question/Answer booklet CHEMISTRY Place one of your candidate identification labels in this box. Ensure the label is straight and within the lines of this box. WA student number: In figures In words Time allowed for this paper Number of additional Reading time before commencing work: ten minutes answer booklets used (if applicable): Working time: three hours Materials required/recommended for this paper To be provided by the supervisor This Question/Answer booklet Multiple-choice answer sheet Chemistry Data booklet To be provided by the candidate Standard items: pens (blue/black preferred), pencils (including coloured), sharpener, correction fluid/tape, eraser, ruler, highlighters Special items: non-programmable calculators approved for use in this examination Important note to candidates No other items may be taken into the examination room. It is your responsibility to ensure that you do not have any unauthorised material. If you have any unauthorised material with you, hand it to the supervisor before reading any further. Copyright © School Curriculum and Standards Authority 2019 Ref: 19-011 *CHE* CHE 2020/1723 Web version of 2019/54771 CHEMISTRY 2 Structure of this paper Number of Number of Suggested Percentage Marks Section questions questions to working time of available available be answered (minutes) examination Section One 25 25 50 25 25 Multiple-choice Section Two 10 10 60 106 35 Short answer Section Three 6 6 70 109 40 Extended answer Total 100 DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Instructions to candidates 1. The rules for the conduct of the Western Australian external examinations are detailed in the Year 12 Information Handbook 2019. Sitting this examination implies that you agree to abide by these rules. 2. Write your answers in this Question/Answer booklet preferably using a blue/black pen. Do not use erasable or gel pens. 3. Answer the questions according to the following instructions. Section One: Answer all questions on the separate Multiple-choice answer sheet provided. For each question, shade the box to indicate your answer. Use only a blue or black pen to shade the boxes. Do not use erasable or gel pens. If you make a mistake, place a cross through that square, then shade your new answer. Do not erase or use correction fluid/tape. Marks will not be deducted for incorrect answers. No marks will be given if more than one answer is completed for any question. Sections Two and Three: Write your answers in this Question/Answer booklet. 4. When calculating numerical answers, show your working or reasoning clearly. Your working should be in sufficient detail to allow your answers to be checked readily and for marks to be awarded for reasoning. Express numerical answers to the appropriate number of significant figures and include appropriate units where applicable. 5. You must be careful to confine your answers to the specific questions asked and to follow any instructions that are specific to a particular question. 6. Supplementary pages for planning/continuing your answers to questions are provided at the end of this Question/Answer booklet. If you use these pages to continue an answer, indicate at the original answer where the answer is continued, i.e. give the page number. 7. The Chemistry Data booklet is not to be handed in with your Question/Answer booklet. See next page  3 CHEMISTRY Section One: Multiple-choice 25% (25 Marks) This section has 25 questions. Answer all questions on the separate Multiple-choice answer sheet provided. For each question shade the box to indicate your answer. Use only a blue or black pen to shade the boxes. Do not use erasable or gel pens. If you make a mistake, place a cross through that square, then shade your new answer. Do not erase or use correction fluid/tape. Marks will not be deducted for incorrect answers. No marks will be given if more than one answer is completed for any question. Suggested working time: 50 minutes. 1. Boric acid, which is a weak acid, was titrated with standardised sodium hydroxide solution. Which one of the indicators listed below would be the most suitable to use in this titration? DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Indicator Range of colour change (pH) (a) thymol blue 1–3 (b) bromocresol green 3.8 – 5.4 (c) cresolphthalein 8 – 10 (d) alizarin yellow 10 – 12 2. The Haber Process involves the following equilibrium reaction: N2(g) + 3 H2(g) ⇌ 2 NH3(g) A number of closed reaction vessels were set up containing the gases shown in the table below. Reaction vessel Gases initially present i nitrogen, hydrogen ii nitrogen iii ammonia iv hydrogen, ammonia In which of the above closed reaction vessels would equilibrium be established after a period of time? (a) i only (b) i and iii only (c) i, iii and iv only (d) ii, iii and iv only See next page CHEMISTRY 4 Questions 3 and 4 refer to the following information. Nitrogen dioxide, NO2(g), is formed when nitrogen monoxide, NO(g), undergoes oxidation as shown below. 2 NO(g) + O2(g) ⇌ 2 NO2(g) ∆H = − 62 kJ mol-1 A change was imposed on an equilibrium gas mixture of NO2, NO and O2. The mixture returned to equilibrium and another change was imposed. The following graph shows the effects of the two changes. NO2 Partial pressure DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF O2 NO First change Second change Time imposed imposed 3. Identify the imposed changes that best account for the shape of the graph. First change Second change (a) the temperature is decreased the partial pressure of O2 is increased (b) the temperature is decreased the partial pressure of NO is decreased (c) the temperature is increased the partial pressure of O2 is increased (d) the temperature is increased the partial pressure of NO is decreased 4. What do the initial partial pressures of the three gases indicate? (a) The relative proportions of the gases present at equilibrium. (b) That there is initially no NO gas present in the system. (c) That the NO2 gas reaches equilibrium first. (d) That the O2 and NO gases are producing NO2 at a faster rate than they are being formed. See next page  5 CHEMISTRY Questions 5, 6 and 7 refer to the following information. The corrosion of brass plumbing fixtures has been identified as a possible cause of the presence of lead in drinking water. Brass is an alloy of copper and zinc but can also contain lead to improve machinability. The corrosion of brass is a redox process, with an electrochemical cell forming on the surface of the brass as illustrated below. DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF 5. Which one of the following correctly identifies the anodic region, cathodic region and direction of electron flow? Direction of Anodic region Cathodic region electron flow (a) Ψ * Ψ* (b) * Ψ Ψ* (c) Ψ * *Ψ (d) * Ψ *Ψ 6. The overall equation for the reaction of lead with oxygen is as follows: 2 Pb(s) + O2(g) + 2 H2O(ℓ)  2 Pb(OH)2(s) What is the theoretical E0 value for the overall Pb/O2 reaction under standard conditions? (a) − 0.27 V (b) + 0.27 V (c) + 0.53 V (d) + 0.93 V 7. The composition of brass can be adjusted by adding various metals. Which one of the following metals would not undergo corrosion if added to brass? (a) silver (b) nickel (c) iron (d) strontium See next page CHEMISTRY 6 8. A distinguishing feature of strong acids is that they (a) produce high concentrations of hydronium ions (H3O+) in solution. (b) have high acidity constants. (c) contain loosely-held hydrogen ions (H+) in solution. (d) ionise rather than dissociate in water. 9. Which one of the following is an alpha amino acid? OH (a) H Se CH COOH (b) H 2N CH CH2 COOH NH2 O DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (c) H 2N CH2 CH2 COOH (d) H2N C NH2 CH COOH Se CH2 COOH 10. Which statement is correct? (a) Fluorine can be oxidised by potassium bromide solution but not by potassium iodide solution. (b) Chlorine can be oxidised by potassium fluoride solution but not by potassium iodide solution. (c) Chlorine can be reduced by potassium bromide solution but not by potassium iodide solution. (d) Bromine can be reduced by potassium iodide solution but not by potassium chloride solution. 11. Which one of the following statements about catalysis in the production of biodiesel is correct? (a) Base catalysis generally has a higher reaction rate but, unlike lipase catalysis, can cause saponification, which decreases the biodiesel yield. (b) The sodium hydroxide and potassium hydroxide used in base catalysis are readily available and relatively cheap, but lipase catalysis produces more toxic waste water. (c) Base catalysis involves only one step, while lipase catalysis involves many steps in its synthesis sequence, which in turn adds to the cost of the process. (d) Base catalysis typically has a lower rate and yield of biodiesel but lipase catalysis is sensitive to alcohols, such as methanol, and has higher energy costs. See next page  7 CHEMISTRY 12. The United Nations Kyoto Protocol and the Intergovernmental Panel on Climate Change aim to secure a global commitment to reducing greenhouse gas emissions over the next few decades. Which of the following equations shows the production of a greenhouse gas? (i) O2 + O  O3 (ii) C + O2  CO2 (iii) CH4 + 2 O2  CO2 + 2 H2O (iv) CO2 + 4 H2  CH4 + 2 H2O (v) NH4NO3  2 H2O + N2O (a) i and ii only (b) ii and iii only (c) iii, iv and v only (d) i, ii, iii, iv and v DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF 13. One method of producing biodiesel is by a transesterification reaction where triglycerides are converted into simpler methyl esters (the biodiesel) of the fatty acids. Which one of the following is a reactant of this transesterification reaction? H H O H C OH (a) H C O C R (b) H C OH H H C OH H H O H O H C O C R H C C OH O O (c) H C O C R (d) H C C OH O O H C O C R H C C OH H H See next page CHEMISTRY 8 14. Which one of the following properties exhibited by octanol is not related to the dispersion forces between the molecules? (a) combustibility (b) melting point (c) solubility in octane (d) solubility in water 15. Which one of the following compounds will not exhibit geometric (cis-trans) isomerism? (a) 1,2-difluoro-1-butene (b) 1,1-difluoro-1-butene (c) 1,2-difluoro-2-butene (d) 1,4-difluoro-2-butene DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF 16. Which one of the following statements about an aqueous solution with a pH less than zero at 25.0 °C is true? (a) Such a solution cannot exist at 25.0 °C. (b) There are no OH−(aq) ions present. (c) The concentration of H+(aq) ions is much greater than the concentration of OH− (aq) ions. (d) There are no H+(aq) ions present as they have formed water molecules through the process of neutralisation. 17. In which of the following sets do all the bolded and underlined atoms have the same oxidation number? (i) H2O, O2, H2O2 (ii) H2O2, NaCℓ, MgH2 (iii) NaCl, Li2CO3, KOH (iv) FeO, Fe2O3, Fe (a) i and iv only (b) ii and iii only (c) iv only (d) i, ii and iii only 18. Which one of the following could not be a product when propan-1-ol is oxidised? (a) CO2 (b) CH3CH2CHO (c) CH3CH2COOH (d) CH3COCH3 See next page  9 CHEMISTRY The following information relates to Questions 19, 20 and 21. A group of Year 12 Chemistry students wanted to know whether increasing ocean acidity increases the rate at which sea shells, CaCO3, dissolve. They went to a beach to collect seawater and sea shells. In their school laboratory they crushed the sea shells and added 2.00 g of the resulting powder to five clean 250 mL beakers, each of which had been placed on top of its own electronic balance. They split the seawater into five portions and bubbled carbon dioxide gas into four of the portions for different amounts of time. This gave the students ‘natural’ seawater plus four seawater samples of different pH. The various seawaters (150 mL portions) were then added to the beakers, with the weight of each beaker and its contents being recorded at timed intervals. 19. Which one of the following proposes a suitable hypothesis for the investigation? (a) As the seawater becomes more acidic, the sea shell powder will dissolve faster. (b) The sea shell powder will dissolve fastest in the most acidic seawater. DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (c) Adding carbon dioxide to seawater changes the pH of the seawater. (d) More of the sea shell powder will dissolve as time progresses. 20. Which one of the following pairs of statements on the validity and reliability of the investigation is correct? Validity Reliability It is valid because the investigation It is reliable because the trials were allows them to determine if seawater performed in a laboratory. (a) pH affects the rate of sea shell dissolution. It is not valid because the investigation It is not reliable because only one trial (b) was simulated in a laboratory and not was performed at each different pH performed in a real ocean. value. It is not valid because the investigation It is reliable because trials were (c) was simulated in a laboratory and not performed at five different pH values. performed in a real ocean. It is valid because the investigation Its reliability could be improved by allows them to determine if seawater conducting multiple trials at each (d) pH affects the rate of sea shell different pH value. dissolution. 21. Which of the following reactions is/are likely to be occurring within the beakers during the investigation? (i) CaCO3(s) + 2 H3O+(aq)  Ca2+(aq) + CO2(g) + 3 H2O(aq) (ii) CaCO3(s) + CO2(aq) + H2O(ℓ) ⇌ Ca2+(aq) + 2 HCO3−(aq) (iii) Ca(OH)2(s) + 2 H3O+(aq) ⇌ Ca2+(aq) + 4 H2O(g) (iv) HCO3−(aq) + H2O(ℓ) ⇌ CO32−(aq) + H3O+(aq) (a) i and ii only (b) i, ii and iv only (c) iii only (d) i, ii, iii and iv See next page CHEMISTRY 10 22. Between which of the following pairs of substances can dispersion forces exist? (i) CH3Cℓ and H2O (ii) CH3CH2CHO and HBr (iii) CH3CH2CH2CH3 and CH3CH2CH2CH2CH2CH3 (iv) CH3CH2CH2OH and NH3 (a) i and ii only (b) i, ii and iii only (c) iii only (d) i, ii, iii and iv 23. Which one of the following is an isomer of pentanoic acid? (a) CH3CHCH-O-CH2CHO (b) CH2CHCH2-O-CH2CH2OH DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (c) OHCCH2CH2CH2CHO (d) CH3CHCHCH2COOH 24. Which one of the following underlined species is acting as an acid? (a) CH3CH2CH2CH2NH2 + CH3COOH ⇌ CH3CH2CH2CH2NH3+ + CH3COO− (b) HSO3− + NH3 ⇌ SO32− + NH4+ (c) NH4+ + CH3COO− ⇌ NH3 + CH3COOH (d) [Fe(H2O)6] 3+ + H2O ⇌ [Fe(OH)(H2O)5]2+ + H3O+ 25. How many isomers does the compound C2H3Br3 have? (a) 1 (b) 2 (c) 3 (d) 4 End of Section One See next page  11 CHEMISTRY Section Two: Short answer 35% (106 Marks) This section has 10 questions. Answer all questions. Write your answers in the spaces provided. Supplementary pages for planning/continuing your answers to questions are provided at the end of this Question/Answer booklet. If you use these pages to continue an answer, indicate at the original answer where the answer is continued, i.e. give the page number. Suggested working time: 60 minutes. Question 26 (9 marks) Dilute hydrochloric acid, HCℓ(aq), is added to three labelled test tubes. (I) Excess copper metal, Cu(s), is added to the first test tube. (II) Excess copper(II) oxide, CuO(s), is added to the second test tube. (III) Excess copper(II) carbonate, CuCO3(s), is added to the third test tube. DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (a) Describe the contents of the first and second test tubes once any reactions are complete. (4 marks) Test Description Tube (I) (II) (b) Write the balanced equation, with appropriate state symbols, for the reaction that takes place between the copper(II) oxide and the hydrochloric acid. (3 marks) If the labels of test tubes (II) and (III) became smudged, describe all the observations that (c) could be used to distinguish between these test tubes once any reactions are complete. (2 marks) See next page CHEMISTRY 12 Question 27 (13 marks) Calcium hypochlorite, Ca(OCℓ)2(s), is used for the treatment of water in swimming pools and is sold as ‘pool chlorine’. (a) Explain why a basic solution is produced when ‘pool chlorine’ is dissolved in the pool water. Include an equation in your answer. (4 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Equation A pool chemical used to counteract the basicity of the pool water is hydrochloric acid, HCℓ(aq). It is sold as ‘pool acid’. (b) State what happens to the pH of the pool water when ‘pool acid’ is added to the pool water. Include an equation to illustrate your statement. (3 marks) Equation See next page  13 CHEMISTRY ‘Pool chlorine’ and ‘pool acid’ must be stored separately from each other because calcium hypochlorite can react explosively on contact with hydrochloric acid. The equation for this reaction is given below. Ca(OCℓ)2(s) + 4 HCℓ(aq)  CaCℓ2(aq) + 2 H2O(ℓ) + 2 Cℓ2(g) (c) Sketch a clearly-labelled energy profile diagram illustrating the reaction between the ‘pool chlorine’ and the ‘pool acid’. (6 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF A spare grid is provided at the end of this Question/Answer booklet. If you need to use it, cross out this attempt and indicate clearly that you have redrawn it on the spare page. See next page CHEMISTRY 14 Question 28 (7 marks) As noted in Question 27, calcium hypochlorite and hydrochloric acid react according to the equation shown below. Ca(OCℓ)2(s) + 4 HCℓ(aq)  CaCℓ2(aq) + 2 H2O(ℓ) + 2 Cℓ2(g) In this reaction, the chlorine in calcium hypochlorite and the chloride from the hydrochloric acid are both converted to chlorine gas. (a) What is the oxidation number for the chlorine in: calcium hypochlorite, Ca(OCℓ)2 hydrochloric acid, HCℓ? (2 marks) calcium hypochlorite hydrochloric acid DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Chlorine gas is produced by the oxidation of one of these substances and the reduction of the other. (b) Write the two half-equations showing how chlorine gas is produced from both substances. (5 marks) Oxidation half-equation Reduction half-equation See next page  15 CHEMISTRY Question 29 (8 marks) Sulfuric acid is a very useful chemical that is produced industrially by a multi-stepped process. These steps are summarised by the following equations. Equation 1 S(ℓ) + O2(g)  SO2(g) Equation 2 2 SO2(g) + O2(g) ⇌ 2 SO3(g) + 198 kJ Equation 3 H2SO4(ℓ) + SO3(g)  H2S2O7(ℓ) Equation 4 H2O(ℓ) + H2S2O7(ℓ)  2 H2SO4(ℓ) When dihydrogen sulfate, H2SO4(ℓ), is mixed with water, it produces sulfuric acid, H2SO4(aq). (a) Combine these equations to produce an overall equation for the production of dihydrogen sulfate, H2SO4(ℓ), from sulfur dioxide, SO2(g). (2 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (b) Complete the following table by listing the advantages and disadvantages of using high temperatures and high pressures for the reaction represented by Equation 2 above. Consider yield, rate, cost and safety. (6 marks) Advantage/s Disadvantage/s High temperature High pressure See next page CHEMISTRY 16 Question 30 (15 marks) Salvarsan is an organic compound that contains the elements: carbon (C), hydrogen (H), arsenic (As), chlorine (Cℓ), nitrogen (N) and oxygen (O). It was one of the first drugs used in chemotherapy and for treating sleeping sickness. The empirical formula of this compound can be determined in a series of analyses. One process involves the reaction of a known mass of Salvarsan with excess strong acid to convert all the chlorine into aqueous chloride ions. (a) Describe the laboratory process involved in determining the mass of chlorine in this sample of Salvarsan once it has been treated with the acid. You should reference any chemicals used and include a balanced equation in your answer. (6 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page  17 CHEMISTRY The results of these analyses using 5.22 g samples determined that it contained: 32.83% carbon by mass 3.21% hydrogen by mass 1.78 g of arsenic 16.18% of chlorine by mass 6.38% of nitrogen by mass. (b) Use this information to calculate the empirical formula of Salvarsan. Show all workings. (9 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page CHEMISTRY 18 Question 31 (13 marks) A solution that contains silver cyanide, AgCN(aq), is used to plate a key with silver. EMF DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (a) Label the above diagram to show the: cathode and anode direction of electron flow direction of ion flow polarity (positive/negative) of each electrode. (4 marks) A salt bridge is required in galvanic cells but is not required in the electroplating cell above. (b) Explain this difference between these two cells. (3 marks) See next page  19 CHEMISTRY Use excerpts from the Material Safety Data Sheet for silver cyanide shown below to answer part (c) and part (d). For copyright reasons this image cannot be reproduced in the online version of this document. (c) Explain why action is taken to maintain the pH above 8 as a safety precaution during the electroplating process using silver cyanide. (3 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page CHEMISTRY 20 Question 31 (continued) (d) Suggest three other safety measures that should be taken during the electroplating process and indicate how each addresses a specific potential hazard to either the workers or the environment. (3 marks) One: Two: DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Three: See next page  21 CHEMISTRY Question 32 (9 marks) From a measuring cylinder, 34.0 mL of 0.114 mol L-1 nitric acid, HNO3(aq), is added to a flask containing 44.5 mL of 0.0556 mol L-1 solution of calcium hydroxide, Ca(OH)2(aq). Determine the pH of the final solution. DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page CHEMISTRY 22 Question 33 (12 marks) Organic molecules have a hydrocarbon skeleton and can contain functional groups that are responsible for the molecules’ characteristic chemical properties. Complete the following tables by (i) writing the structural formula of each compound listed (ii) writing the structural formula of the organic product from the reaction (iii) naming the organic product from the reaction. When writing the structural formula, show the bonds between carbon atoms and within any functional group e.g. CH3 CH2 C CH3 O DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Name of compound Structural formula of compound pent-2-ene Structural formula of organic product Reacts with Br2(aq) Name of organic product See next page  23 CHEMISTRY Name of compound Structural formula of compound ethanal Structural formula of organic product Reacts with KMnO4(aq) / H+(aq) Name of DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF organic product Name of compound Structural formula of compound butanoic acid Structural formula of organic product Reacts with Na2CO3(aq) Name of organic product See next page CHEMISTRY 24 Question 34 (12 marks) Consider the reaction between magnesium carbonate, MgCO3(s), and dilute nitric acid, HNO3(aq). MgCO3(s) + 2 H+(aq)  Mg2+(aq) + CO2(g) + H2O(ℓ) The following data was obtained from the addition of excess 0.500 mol L-1 nitric acid to 5.00 g of magnesium carbonate. Time (min) 0 1.0 2.0 3.0 4.0 5.0 6.0 Volume of gas produced (mL) 0 12 18 25 32 33 33 (a) Draw a labelled graph of the data provided in the grid below. (4 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF A spare grid is provided at the end of this Question/Answer booklet. If you need to use it, cross out this attempt and indicate clearly that you have redrawn it on the spare page. See next page  25 CHEMISTRY (b) Explain the shape of your graph in part (a) by referring to Collision Theory. (6 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (c) Sketch and label a line on your graph in part (a) that shows the effect of conducting the same experiment at a higher temperature. (2 marks) See next page CHEMISTRY 26 Question 35 (8 marks) Consider the following acid-base titration curve that is produced by the addition of 0.166 mol L-1 sodium hydroxide solution to 20.00 mL of an approximately 0.1 mol L-1 diprotic acid. 12 10 8 pH 6 4 2 DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF 0 6 12 18 24 30 Volume of NaOH added (mL) (a) (i) Indicate whether the diprotic acid is most likely to be sulfuric acid, H2SO4(aq) or sulfurous acid, H2SO3(aq), by circling your choice below. (1 mark) Sulfuric acid Sulfurous acid (ii) Making reference to the titration curve shown above, give two reasons for your answer. (2 marks) One: Two: See next page  27 CHEMISTRY (b) Predict the effect (increase, decrease or no change) on the calculated concentration of the acid for the following two systematic errors that can occur in a titration and justify your choice. (4 marks) Effect on calculated Systematic Error concentration Justification of acid (circle) I Only rinsing the pipette with distilled increase water before use decrease no change DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF II Using an indicator with an end point of increase pH = 4.5 decrease no change (c) State one reason why these errors are classified as systematic errors rather than random errors. (1 mark) End of Section Two See next page CHEMISTRY 28 Section Three: Extended answer 40% (109 Marks) This section contains six questions. You must answer all questions. Write your answers in the spaces provided. Where questions require an explanation and/or description, marks are awarded for the relevant chemical content and also for coherence and clarity of expression. Lists or dot points are unlikely to gain full marks. Final answers to calculations should be expressed to the appropriate number of significant figures and include appropriate units where applicable. Supplementary pages for planning/continuing your answers to questions are provided at the end of this Question/Answer booklet. If you use these pages to continue an answer, indicate at the original answer where the answer is continued, i.e. give the page number. Suggested working time: 70 minutes. DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Question 36 (20 marks) The ideal pH of human blood is 7.4. If the pH of a person’s blood varies too much from this value, a serious condition can develop. If the pH is too low, it is called acidosis; if the pH is too high, it is called alkalosis. Death may occur if the pH drops below 6.8 or rises above 7.8. One buffer system for maintaining acid-base balance in blood is the carbonic acid-hydrogencarbonate buffer. During exercise, the muscles need more oxygen to produce energy. They produce carbon dioxide, CO2, and hydronium ions, H3O+, which move from the muscles to the blood. The relevant equilibrium equations for the carbonic acid-hydrogencarbonate buffer system are shown as follows. Equation 1 H3O+(aq) + HCO3−(aq) ⇌ H2CO3(aq) + H2O(ℓ) (a) Identify the two conjugate acid-base pairs on Equation 1 above, indicating clearly which is the acid and which is the base in each pairing. (2 marks) See next page  29 CHEMISTRY (b) Write the equilibrium constant expression for Equation 1. (2 marks) Carbonic acid further reacts to form water and carbon dioxide as shown in Equation 2. Equation 2 H2CO3(aq) ⇌ H2O(ℓ) + CO2(aq) (c) Combine Equations 1 and 2, to create an overall equation that shows the relationship between HCO3−(aq) and CO2(aq). (2 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (d) Identify the effect on the blood’s pH when each of the following components are removed: carbon dioxide and hydrogencarbonate ions. (2 marks) Effect on pH Component removed (circle your answer) carbon dioxide increase decrease no effect hydrogencarbonate ions increase decrease no effect See next page CHEMISTRY 30 Question 36 (continued) The buffering capacity of the carbonic acid-hydrogencarbonate is greatest when the pH is between 5.1 and 7.1. (e) State two conditions in terms of concentration that are necessary for this buffering capacity to be optimal. (2 marks) One: Two: DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF When the pH of the blood is too high, the kidneys can remove hydrogencarbonate ions, HCO3−, from the blood. (f) Use Le Châtelier’s Principle to demonstrate that the kidneys’ action can help to prevent excessively high blood pH. (3 marks) See next page  31 CHEMISTRY When inhaling, oxygen is taken into the lungs and transferred to the blood; when exhaling, carbon dioxide is expelled. During hyperventilation (very rapid and deep breathing) more carbon dioxide is being expelled from the body than it can produce. This upsets the oxygen/carbon dioxide balance and can cause dizziness and fainting. Hyperventilating results in lowering the carbon dioxide concentration in the blood, which can affect the pH of the blood. The equation shown below illustrates the formation of hydronium ions within the blood system. 2 H2O(ℓ) + CO2(aq) ⇌ H3O+(aq) + HCO3−(aq) A first-aid treatment for hyperventilation is the ‘paper-bag treatment’ whereby the patient breathes into a paper bag and so breathes back in the expelled breath, which contains a higher concentration of carbon dioxide. (g) State the effect of the ‘paper-bag treatment’ on the pH of the blood and explain why it is DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF an effective treatment for hyperventilation. (3 marks) Another contributor to a potential imbalance of blood pH is the formation of lactic acid. The chemical name for lactic acid is 2-hydroxypropanoic acid, C₃H₆O₃. (h) Draw the structural formula for lactic acid with all its functional groups circled and labelled. (4 marks) See next page CHEMISTRY 32 Question 37 (24 marks) Detergents and soaps are both used as cleaning agents. The general structure of a detergent is given below. H H H H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C C C O H H H H H H H H H H H H H H H H H S O– O (a) Explain how detergents are able to remove grease from a surface by referring to the intermolecular forces present. Include a labelled diagram to illustrate your answer. (7 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page  33 CHEMISTRY Detergents are considered to be more versatile cleaners than soap. (b) Explain why soaps are generally less effective than detergents as cleaning agents in hard water. Include a relevant equation in your answer. (4 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page CHEMISTRY 34 Question 37 (continued) Alkenes can also form soaps. (c) Draw a structural diagram for the soap ion, C17H31CO2− using the incomplete structure below. Show all atoms and bonds. (2 marks) C C C C C C C C C C C C C C C C C DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (d) Write an equation showing the formation of this soap from the fat (triglyceride) shown below. (3 marks) C17H31COOCH2 C17H31COOCH + C17H31COOCH2 See next page  35 CHEMISTRY The formation of soap is both an endothermic and equilibrium reaction. (e) Predict and explain the conditions that would result in the highest yield of soap in the shortest amount of time. (8 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page CHEMISTRY 36 Question 38 (18 marks) Polymethyl methacrylate and polycarbonate are two polymers that are used as alternatives to glass. Polymethyl methacrylate is more commonly known as Perspex or plexiglass and is an addition polymer, while polycarbonate is a type of condensation polymer. Both polymers are transparent to visible light and have other properties as listed below. Polymethyl methacrylate Polycarbonate lightweight moderate chemical resistance moderate UV resistance high heat resistance low impact strength high impact strength low chemical resistance low scratch resistance low heat resistance low UV resistance DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF (a) For the following uses as an alternative to glass, identify which polymer would be the more appropriate. Justify your choice of polymer by comparing the effect of two relevant properties as listed for both polymers. (4 marks) Use Choice of polymer Justification Skylight Safety glasses See next page  37 CHEMISTRY The monomer, methyl methacrylate, can be formed from the esterification of methanol and methacrylic acid (2-methylprop-2-enoic acid). The structural formula of methyl methacrylate is shown below. H3 C O CH3 C C H 2C O (b) Write a balanced equation for the esterification of methanol and methacrylic acid. Show the full structural formula of each species in the equation. (4 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Methyl methacrylate can undergo addition polymerisation to form polymethyl methacrylate. (c) Draw a section of a polymethyl methacrylate showing all atoms and at least three repeating units of the monomer. (3 marks) See next page CHEMISTRY 38 Question 38 (continued) One method for the production of methacrylic acid is by the following oxidation. oxidation C4 H 8 O C4H6O2 methylpropenol isomer methacrylic acid (d) Suggest an assumption that must be made regarding the mole ratios of product to reactant for this reaction and then determine the mass of the methylpropenol isomer required to produce 1.50 tonne of methacrylic acid if the efficiency of this oxidation is 65%. (Note: 1 tonne = 1000 kg.) (5 marks) Assumption: DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Calculation: See next page  39 CHEMISTRY Polycarbonates are condensation-type polymers for which the by-product is hydrogen chloride instead of water. The two monomers for polycarbonate are shown below. CH3 Cl HO OH Cl O CH3 (e) Why is polymethyl methacrylate classified as an addition polymer, while polycarbonate is classified as a condensation polymer? (2 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page CHEMISTRY CHEMISTRY 42 40 Question Question3939 (13 (13 marks) marks) Herbicides Herbicidesare arechemicals chemicalsthat thatkill kill plants, plants, including weeds. The including weeds. The label labelofofa acommercially-available commercially available pesticide concentrate is shown below. herbicide concentrate is shown below. Generic Weed Killer Fast, effective, easy to apply. Recommended by professional gardeners. Ingredients: 155 155g/L g/L±±5.00% 5.00 %sodium sodiumchloride chloride For copyright reasons this image cannot be reproduced 295 295g/L g/L±±5.00% 5.00 %acetic acetic(ethanoic) (ethanoic)acid acid in the online version of this document, but may be viewed at the link listed on the acknowledgements page. DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF A chemist A chemist waswas given given the the task task ofof verifyingthe verifying theconcentrations concentrationsofofsodium sodiumchloride chlorideand andacetic acetic(ethanoic) (ethanoic) acid stated for acid stated for this herbicide.this herbicide. TheThe sodium sodium chloride chloride content content of of thethe herbicide pesticide was was analysed. analysed. It was It was found found to be to be consistent consistent within within the the tolerance of ± 5.00% of the stated concentration. The chemist then performed a series tolerance of ± 5.00 % of stated concentration. The chemist then performed a series of titrations of with titrations sodium with sodium hydroxide hydroxide to measure to measure the acetic the acetic (ethanoic) (ethanoic) acid concentration. acid concentration. TheThe herbicide herbicide solution solution used used in the in the titrations titrations waswas prepared prepared byby pipetting pipetting 5.00 5.00 mLmL of of thethe concentrate into a 250.0 mL volumetric flask. The solution in the flask was then made up to the mark up concentrate into a 250.0 mL volumetric flask. The solution in the flask was then made to the with distilled water. mark with distilled water. A 20.00 A 20.00mLmLsample of of sample thethe diluted herbicide diluted herbicidewas waspipetted pipetted into a conical into flask a conical and flask a few and drops a few dropsof of a suitable indicator were added. This solution was then titrated with standardised 0.0947 mol a suitable indicator were added. This solution was then titrated with standardised 0.0947 mol L-1 L -1 NaOH NaOH solution. solution. Four titrations After were an initial performed. ‘rough titration’,The resultsfour a further aretitrations shown inwere the following table. performed. The results are shown in the following table. (a) Complete the table and determine the average titre. (2 marks) (a) Complete the table and determine the average Titration titre. Burette Readings (mL) (2 marks) Number Initial Final Titre 1 Titration 1.28 Burette readings 20.75 (mL) 2 number 0.75 20.19 Initial Final Titre 3 1.48 21.82 4 1 0.51 1.28 19.90 20.75 Average titre 2 20.75 40.19 3 1.48 21.82 4 21.82 41.21 Average titre SeeSee next page next page  41 CHEMISTRY (b) Identify with what solution each of these pieces of glassware should be rinsed prior to their use in these titrations. (3 marks) Glassware item Rinse solution 5.00 mL pipette 20.00 mL pipette 250.0 mL volumetric flask (c) Demonstrate whether or not the experimentally-determined value of the acetic (ethanoic) acid concentration matches the value given on the herbicide label, bearing in mind that a difference of ± 5.00% is considered acceptable. Show all workings and reasoning. (8 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF See next page CHEMISTRY 42 Question 40 (22 marks) A chemist was developing a new method for extracting lithium metal from ores rich in the mineral lepidolite. The procedure being proposed by the chemist is as follows: Step 1 crush and grind the ore Step 2 (Leach) add sulfuric acid to the crushed ore to dissolve lepidolite (and other soluble ore constituents) Step 3 add reagents to the leach solution that will precipitate unwanted soluble species Step 4 recover lithium as lithium carbonate. In a test of Step 2, performed by the chemist, 5.0 L of sulfuric acid, which was in excess, was added to a crushed and ground sample of a lepidolite-containing ore. The leach solution was analysed and found to contain sulfate ions and hydrogen ions from the sulfuric acid and the ions stated in the table below. DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF Ions present Concentration Li+ 2.13 g L-1 Rb+ 1.30 g L-1 Aℓ 3+ 1.86 g L-1 Fe (as Fe2+ and Fe3+) 1.27 g L-1 The chemist tried to remove the rubidium and aluminium ions from the leach solution by cooling the solution to 5.00 °C so as to precipitate them as rubidium alum, RbAℓ(SO4)2. The equation is shown below. Rb+ (aq) + Aℓ 3+ (aq) + 2 SO42− (aq)  RbAℓ(SO4)2 (s) The chemist found that, while all of the Rb+ precipitated, there was a considerable quantity of Aℓ 3+ ions still dissolved in the leach solution. (a) Calculate the concentration of Aℓ 3+ ions remaining in the 5.0 L of leach solution. Give your answer in grams per litre (g L-1) to the appropriate number of significant figures. (9 marks) See next page  43 CHEMISTRY DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF To remove the remaining Aℓ 3+ ions from the leach solution, the chemist added 2.63 L of a 0.0550 mol L-1 K2SO4 solution, with the result being the precipitation of potassium alum as shown in the equation below. K+(aq) + Aℓ 3+(aq) + 2 SO42−(aq)  KAℓ(SO4)2(s) The sulfate ions remained in excess due to the initial addition of sulfuric acid. (b) Was sufficient K2SO4 solution added to precipitate all of the Aℓ 3+ ions remaining in the leach solution? Justify your answer with relevant calculations. (4 marks) See next page CHEMISTRY 44 Question 40 (continued) The final purification step was the removal of iron from the leach solution. To do this the chemist added a suitable oxidant (1.00 mol L-1 hydrogen peroxide) to convert all of the Fe2+ ions to Fe3+ ions. The chemist then added excess sodium hydroxide solution to precipitate all of the iron (now present as Fe3+ ions) as Fe(OH)3. This precipitate, and the alum precipitates formed earlier, were removed by filtration. (c) Write a balanced overall equation to show the conversion of Fe2+ to Fe3+ by hydrogen peroxide. (3 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF The leach solution, now free from rubidium, aluminium and iron, was heated and evaporated to dryness, yielding a lithium-rich residue. The residue was further treated to produce lithium carbonate suitable for use in lithium-ion battery manufacture, with the mass of lithium carbonate recovered being equal to 46.7 g. (d) Calculate the percentage yield of lithium carbonate, Li2CO3, based on the theoretical amount that should have been recovered. Use the concentration of Li+(aq) in the table on page 42. (6 marks) See next page  45 CHEMISTRY Question 41 (12 marks) When insects touch a spider’s web they become stuck and therefore, easy prey for the spider. The insects become stuck because the web is coated with a glue-like substance produced by the spider. The ‘spider glue’ consists of water, proteins, ionic salts and polar carbon compounds. The structural formula given below shows a small section of a spider glue protein. H H O H H O O H O H O N C C N C C N C C N C C N C C H C H H H H H H CHOH H CH3 (a) List the names of the amino acids in the order in which they were drawn in the section of DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF the protein given above. Do not use abbreviations. (3 marks) (b) Circle one peptide bond in the above structure. (1 mark) See next page CHEMISTRY 46 Question 41 (continued) (c) What is the difference between the primary structure and the secondary structure of a protein? (2 marks) When spider glue is washed with water, the ionic salts and polar carbon compounds dissolve. The proteins do not dissolve and remain on the silk strand. The following diagram shows what DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF happens. UNWASHED SPIDER SILK wash water silk strand Glue droplet containing water, proteins, ionic salts and polar carbon compounds. WASHED SPIDER SILK silk strand proteins Wash water containing dissolved ionic salts and polar carbon compounds. See next page  47 CHEMISTRY (d) Explain why the polar carbon compounds dissolve in water but the proteins do not. Illustrate your answer with the aid of a labelled diagram. (6 marks) DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF End Seeofnext questions page  CHEMISTRY Question number: Supplementary page 48 DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF CHEMISTRY 49 Supplementary page Question number: DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF  CHEMISTRY Question number: Supplementary page 50 DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF CHEMISTRY 51 Supplementary page Question number: DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF  CHEMISTRY Question number: Supplementary page 52 DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF CHEMISTRY 53 Supplementary page Question number: DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF  Spare grid CHEMISTRY 54 DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF CHEMISTRY 55 Spare grid DO NOT WRITE IN THIS AREA AS IT WILL BE CUT OFF  ACKNOWLEDGEMENTS Question 31 Heatherawalls. (2014). EIG blue key.svg [Image]. In Wikimedia. Retrieved May, 2019, from https://commons.wikimedia.org/wiki/File:IEG_blue_key.svg Used under Creative Commons Attribution-ShareAlike 3.0 Unported licence Excerpts from: Fisher Scientific. (2008). Material Safety Data sheet - Silver Cyanide, 99%. Retrieved May, 2019, from https://fscimage.fishersci.com/msds/07459.htm Question 39 Arcady. (n.d.). Tested-certified-stamp [Image]. Retrieved May, 2019, from https://www.shutterstock.com/image-vector/tested-certified-stamp- 285118331?src=PBnXIxQ41C903NbjEJq4uA-1-5 Unknown. (n.d.). Dandelion Weed Clipart [Image]. Retrieved May, 2019, from http://worldartsme.com/dandelion-weed-clipart.html This document – apart from any third party copyright material contained in it – may be freely copied, or communicated on an intranet, for non-commercial purposes in educational institutions, provided that it is not changed and that the School Curriculum and Standards Authority is acknowledged as the copyright owner, and that the Authority’s moral rights are not infringed. Copying or communication for any other purpose can be done only within the terms of the Copyright Act 1968 or with prior written permission of the School Curriculum and Standards Authority. Copying or communication of any third party copyright material can be done only within the terms of the Copyright Act 1968 or with permission of the copyright owners. Any content in this document that has been derived from the Australian Curriculum may be used under the terms of the Creative Commons Attribution 4.0 International (CC BY) licence. 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