ST STITHIANS COLLEGE DEPARTMENT OF PHYSICAL SCIENCE PRELIMINARY EXAMINATIONS 2012 GRADE 12 PHYSICAL SCIENCE: PAPER 2

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1 Page 1 of 15 ST STITHIANS COLLEGE DEPARTMENT OF PHYSICAL SCIENCE PRELIMINARY EXAMINATIONS 2012 GRADE 12 PHYSICAL SCIENCE: PAPER 2 Examiners Moderators: Miss S Nargaroo (Girls College), Mr SB Lambson Mr SB Lambson Maximum time: 3 hours (+ 10 minutes reading time) Marks: 200 INSTRUCTIONS 1. This paper consists of FIFTEEN (15) pages. Please ensure that you have all of them 2. Read the questions carefully. 3. Answer the questions in the answer booklet provided 4. Graph paper is provided 5. It is in your own interest to write legibly and to present your work neatly. 6. Ensure that the numbering of the questions is correct. 7. Show all your workings, where necessary. 8. A data sheet is provided which may be used to assist you in answering the questions

2 Page 2 of 15 QUESTION ONE - Multiple Choice In each of the following questions 4 possible answers are provided. Write down only the number of the question and the letter of the corresponding answer Compound X is mixed with bromine water. The brown colour of the bromine disappears almost immediately. Which one of the following represents compound X? A. C 2 H 4 B. C 3 H 8 C. CH 3 OH D. C 2 H Which one of the following is not a property or characteristic of the hydrocarbons? A. They can undergo combustion reactions B. They comprise of only two different types of elements. C. They are non polar molecules. D. They are reactive molecules What is the IUPAC name of the following compound? H H H H C C C C H CH 3 H CH 3 A. 2,4-dimethyl but-1-ene B. 1,3-dimethyl but-1-ene C. 1,3-methyl but-1-ene D. 2-methyl pentene.

3 Page 3 of In a series of experiments 0,05g samples of magnesium were added separately to 100cm 3 volumes of hydrochloric acid. The table below summarises the experimental conditions: Expt Mg(s) HCl(aq) Temp of acid( C) (mol.dm 3 ) i ribbon 0,1 25 ii ribbon 0,5 25 iii powder 0,1 70 iv powder 0,5 25 v powder 0,1 20 Which of the combination of experiments would magnesium be expected to take the least amount of time to completely react with the excess hydrochloric acid? A. I and ii B. iii and iv C. iii and v D. ii and iv 1.5. The rate of the reaction between zinc granules and dilute sulphuric acid can be increased by adding a solution of copper sulphate. The reason for this is that the A. Zinc displaces the copper from the copper sulphate. B. Sulphuric acid reacts more vigorously with the copper. C. Concentration of the sulphate ions increases. D. Copper ions act as a catalyst One of the stages in the industrial preparation of iron from its ore is represented by the equation below: Fe 2 O 3 (s) + 3CO (g) 2Fe (l) + 3CO 2 (g) Δ H < 0 The following possible disturbances can be made to the equilibrium system: (i) (ii) (iii) Pressure may be increased. CO 2 may be removed. Temperature may be increased Which of the changes mentioned above will favour the forward reaction? A. (i), (ii) and (iii) B. (i) and (ii) only C. (ii) only D. (iii) only

4 Page 4 of Consider the following reactions with a metal M. (i) M reacts with a solution of AgNO 3, causing a deposit of metallic Ag to form. (ii) M does not react with a solution of ZnSO 4. The correct way to list the metals M, Ag and Zn in order of decreasing strength as reducing agents is: A. M, Ag, Zn B. Zn, M, Ag C. Ag, M, Zn D. Ag, Zn, M 1.8. The most common filling for tooth cavities is dental amalgam a solid solution of tin and silver in mercury. If you bite on a piece of aluminium foil that is in contact with a dental filling in your mouth, you may feel a painful sensation because A. the aluminium foil is hard. B. a temporary galvanic cell has been set up whilst the aluminium and filling are in contact. C. electrons are being transferred to the aluminium. D. a temporary electrolytic cell has been set up whilst the aluminium and filling are in contact. 1.9 Consider the following redox reaction: Br 2 (l) + 2I (aq) 2Br (aq) + I 2 (s) Which one of the following deductions about this reaction is correct? A. bromine is oxidised. B. bromine acts as a reducing agent. C. the iodide ions are oxidised. D. iodine acts as a reducing agent.

5 Page 5 of The diagram below shows the energy distribution curves for molecules of a sample of a liquid at two different temperatures. Which of the following statements about the graph is incorrect? A B C D At T 2 the number of molecules with greater E k is decreased. At T 1 the number of molecules with greater E k is decreased. The shaded area represents the number of molecules with enough energy to react. Temperature of a substance is related to the kinetic energy of the molecules. 20 marks

Page 6 of 15 QUESTION TWO 2.1 Provide definitions for the following: 2.1.1 homologous series. (2) 2.1.2 hydrogenation. (2) 2.2 Draw structures for the following organic compounds: 2.2.1 3 dimethyl, pent-1-yne.

6 Page 6 of 15 QUESTION TWO 2.1 Provide definitions for the following: homologous series. (2) hydrogenation. (2) 2.2 Draw structures for the following organic compounds: dimethyl, pent-1-yne. (structural formula) (2) propan-1,2,3-triol. (condensed formula) (2) methyl pentanoate. (semi-structural formula) (2) 2.3 Propane and butane are used as propellants in spray cans in place of chloflourocarbons (CFCs) Name the homologous series to which both propane and butane belong and give the general formula of this series. (2) The molecule butane can be found in nature in another isomeric form (a) What is meant by the term isomeric form? (2) (b) (c) Draw the semi-structural formula and name the other isomeric form of butane. (3) The two isomers will have distinctly different boiling points. Which isomer will have the greater boiling point? Explain your reasoning. (4)

7 Page 7 of Both propane and butane are able to undergo combustion reactions. Below is the combustion reaction of propane C 3 H 8 + 5O 2 3CO 2 + 4H 2 O (a) What is meant by the term combustion? (2) (b) (c) If 39,2dm 3 of propane gas reacts completely, what volume of CO 2 gas would be formed? (assume all gases are at STP) (3) If butane gas has to now react, what mass of butane would be required to react completely with 53,9dm 3 of oxygen gas at STP? (5) 2.4 Nowadays newer alternatives to CFC s are hydrochloroflourocarbons (HCFCs) and hydroflourocarbons(hfcs) such as CH 2 FCH Draw the structural formula for CH 2 FCH 3 and give the IUPAC name for this compound. (3) CFC s have been totally banned from use in society. Briefly explain why this ban was introduced. (2) QUESTION THREE Consider the following organic compounds, all of which contain oxygen in their structure. A. CH 3 COCH 3 B. CH 3 CH 2 COOH C. CH 3 CH 2 CHO D. CH 3 CH 2 CH 2 OH 36 marks 3.1. Name the homologous series to which compound A belongs (1) 3.2. Which compound is an isomer of A? (1) 3.3 What name is given to the functional group of compound B? (1) 3.4 Compounds B and D can react together to form an ester Name the ester that is formed. (2) Name the substance that is added to the reaction which acts as a dehydrating agent in the reaction. (1) Why is it important to add a dehydrating agent in this reaction? (3) Explain why an esterification reaction should always be performed in a hot water bath and never over an open flame. (2) 11 marks

8 Page 8 of 15 QUESTION FOUR 4.1 Polymers are formed by either addition or condensation type reactions. Consider the semi structural formula of the polymer below: Define the term polymer (2) Would this be an addition or condensation type polymer? Explain you answer (3) Identify the homologous series to which the individual monomers belong (2) In terms of propagation of this polymer, what is significant about the structure of the monomer units that are used in this type polymerisation reaction? (4) Study the structure of the polymer given above and write down the semi structural formula of one repeating unit. (2) What molecule would be released every time a repeating unit is formed? (1) 4.2 Plastics are man made macromolecules and they are divided into two groups, namely thermosets and thermoplastics. Briefly explain the structural differences between these two types of plastics. (4) 18 marks

9 Page 9 of 15 QUESTION FIVE A number of basic organic reactions are shown in the flow diagram below. X B C 3 H 6 C Y + F 2 A + Br 2 C 3 H 7 Br D C 3 H 7 OH 5.1 Name the type of reactions shown by A, B C and D. (4) 5.2 Write down the molecular formula for compound X. (1) 5.3 Using structural formulae, show the product of reaction C. (2) 5.4 Write down the IUPAC name for compound Y. (2) 5.5 What homologous series does compound Y belong to? (1) 10 MARKS

10 Page 10 of 15 QUESTION 6 Antacids are used to relieve indigestion (the condition when the stomach produces too much acid resulting in an uncomfortable and painful feeling). A certain antacid tablet dissolves in water and reacts with the acid in the stomach to release carbon dioxide gas.a group of learners want to investigate the effect of temperature on the rate of dissolving of this antacid tablet in water. Design an investigation that the group of learners can conduct by answering the questions that follow: 6.1. State a hypothesis for this investigation. (2) 6.2 Is it better to take the antacid tablet with warm water or cold water. Give a reason for your answer. (2) 6.3. The active ingredient in most antacid tablets is calcium carbonate which reacts with the hydrochloric acid in the stomach according to the reaction: CaCO 3 (s) + 2 HCl (aq) CaCl 2 (aq) + H 2 O (l) + CO 2 (g) Some students set up an experiment that collected the carbon dioxide gas released and measured the volume of gas collected every half minute. The results of the experiment are shown in the table below. Time (minutes) Volume of gas(cm 3 ) 0 0 0, , , , ,5 35, , Name the independent variable in this experiment. (1) Identify 2 variables that need to be controlled. (2) Plot a graph of gas production versus time on the graph paper provided. (6) At what time did the reaction run to completion? (1)

11 Page 11 of Using molecular collision theory, explain the shape of the graph between t = 0 and t = 3 minutes. (4) If the mass of calcium carbonate in one antacid tablet is 700mg, calculate the volume of 0,1 mol.dm -3 hydrochloric acid that would be neutralised by one tablet. (5) 23 marks QUESTION SEVEN Sulphuric acid is made using the industrial process known as the Contact process at 430 o C. This process allows sulphur dioxide to react with oxygen forming sulphur trioxide according to the equilibrium reaction shown below : 2SO 2 (g) + O 2 (g) 2SO 3 (g) H= -192kJ Does the forward reaction represent an exothermic or endothermic reaction? Give a reason for your answer (2) 7.2 Draw a neat energy profile for the forward reaction. Include the following labels on your profile : activation energy energy of reactants energy of products activated complex heat of reaction energy of product formation (5) 7.3 The Contact process gets its name due the contact that the reactant molecules make with the surface of a catalyst that is added at the start of the reaction Define the term catalyst (2) Using the energy profile drawn in 6.2, draw and explain how the addition of a catalyst will affect the shape of the profile. (3) 7.4 Define the term dynamic chemical equilibrium (3) 7.5 By writing down only the words INCREASE, DECREASE or STAYS THE SAME, state the effect the following changes will have on the amount of SO 2 produced when the system is at equilibrium SO 3 is removed from the reaction vessel The temperature of the system is decreased The pressure in the system is decreased More catalyst is added to the system (4)

12 Page 12 of When equilibrium is reached at C, it was found that 0, 2 mol of SO 2, 0,4mol of O 2 and 0,2mol SO 3 were formed in a 2dm 3 container. Calculate the equilibrium constant for this reaction at this temperature. (4) 7.7 By considering the reaction, the best conditions to produce high yields of SO 3 are at low temperatures and high pressures Explain why will these conditions are considered to be ideal? (4) Practically, the reaction takes place at the relatively high temperature of C and a relatively low pressure of 2 atmospheres. Explain why these less than ideal conditions are actually used in industry. (4) 7.8 Consider the graph shown below which illustrates how the rate of formation of SO 3 changes with time in the Contact process. 12 This graph shows the changes in reaction rates for a period of 14 minutes What do the solid and broken lies represent on this graph? (2) Why do these lines have the curved shapes as seen on the graph? (2) When does the reaction reach equilibrium for the first time? (1) Explain what has happened to the reaction between t = 8 and t = 12 minutes (4) How will the equilibrium constant, K c be affected by this disturbance? Use INCREASE, DECREASE or STAYS THE SAME. (2) 42 marks

13 Page 13 of 15 QUESTION EIGHT V Copper electrode Chromium electrode X Copper (II) sulphate solution Cotton wool plugs Chromium (III) sulphate solution Consider the diagram of a copper chromium Galvanic cell above. The copper electrode is placed in a copper(ii) sulphate solution while the chromium electrode is placed in a solution of chromium(iii)sulphate Write down the chemical formula of chromium(iii) sulphate (1) Define the term oxidation (1) Write down the chemical half reactions for the two redox processes that occur in each half cell. (2) Which electrode acts as the anode? ( write down only Cu or Cr) (1) Write down the net ionic equation that occurs in this cell. (2) What are the standard electrochemical conditions under which this cell was set up? (2) Calculate the cell emf under these standard conditions. (2) Is the reaction that occurs in this cell spontaneous? Explain your answer by referring to your calculation above. (2)

14 Page 14 of Consider the component labelled X in the diagram (a) Name the component X (1) (b) Suggest a suitable chemical reagent that might be used in X (1) (c) Give two possible functions of component X (2) Write down the cell notation for this Galvanic cell. (4) 21 marks QUESTION NINE Consider the diagram below of an electrolytic cell involving the electrolysis of a concentrated silver chloride solution + Power source - Graphite electrodes AgCl (aq) 9.1 Explain the difference between a Galvanic and an electrolytic cell? (2) 9.2 Which electrode would be the cathode in this cell? (1) 9.3 What would be observed at the anode when the power source is switched on? Write down the half reaction to explain this observation. (2)

15 Page 15 of Calculate the mass of silver deposited if a current of 1,5A is allowed to flow through the circuit for 2 minutes. (6) ( charge on e - = 1,6 x C N A = 6,02 x ) 9.5 It is important to ensure that the AgCl solution is concentrated during this electrolytic process What would be observed if a dilute solution of AgCl was used? (2) Write down the half reaction to support this observation. (2) 9.6 The silver chloride solution is now replaced with a concentrated solution of sodium chloride. Instead of the expected sodium metal being formed, it was observed that hydrogen gas was seen bubbling at the electrode. Using half reactions, explain why this has happened. (4) 19 marks

ST STITHIANS BOYS COLLEGE

Page 1 of 15 ST STITHIANS BOYS COLLEGE DEPARTMENT OF PHYSICAL SCIENCE PRELIMINARY EXAMINATIONS 2011 GRADE 12 PHYSICAL SCIENCE : PAPER II Examiners : Mr B Nozaic and Mr P Mphaphuli (Boys College) Moderator