CHEMISTRY HIGHER LEVEL

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1 *P15* Pre-Leaving Certificate Examination, 2013 Triailscrúdú na hardteistiméireachta, 2013 CHEMISTRY HIGHER LEVEL TIME: 3 HOURS 400 MARKS Answer eight questions in all These must include at least two questions from Section A All questions carry equal marks (50) The information below should be used in your calculations. Relative atomic masses: H = 1, C = 12, O = 16, Na = 23, Cl = 35.5, Ca = 40, Cr = 52 Molar volume at s.t.p. = 22.4 litres Avogadro constant = mol 1 Universal gas constant, R = 8.3 J K 1 mol 1 Page 1 of 8

2 Section A Answer at least two questions from this section [see page 1 for full instructions] 1. In an experiment the primary standard ammonium iron(ii) sulphate ((NH 4 ) 2 SO 4.FeSO 4.6H 2 O) was used to standardise a solution of potassium manganate(vii) (KMnO 4 ). 25 cm 3 of a 0.01 M ammonium iron(ii) sulfate and 10 cm 3 of dilute sulfuric acid were placed in a clean dry conical flask. The potassium manganate(vii) was placed in the burette. After a number of titrations it was found that the average titre was 23.4 cm 3. MnO 4 + 5Fe H + Mn Fe H 2 O Explain the underlined term. Why is potassium manganate(vii) not considered to be a primary standard? (9) Why was sulfuric acid added to the conical flask? (5) (c) (e) (f) (g) Name the piece of equipment that should be used to transfer the 25 cm 3 of ammonium iron(ii) sulfate to the conical flask. (3) Describe the correct procedure for rinsing this piece of equipment and transferring the solution to the conical flask. (9) What colour change would you observe as the solution from the burette flows into the conical flask? (6) How was the end-point detected? (3) What is the role of the Mn 2+ ions produced in this reaction? (6) 25 cm 3 of a 0.01 M ammonium iron(ii) sulfate required 23.4 cm 3 of potassium manganate(vii) solution for complete reaction. MnO 4 + 5Fe H + Mn Fe H 2 O Calculate the concentration of potassium manganate(vii) (i) in moles per litre, (ii) in g/litre. (9) [ Relative atomic masses: K = 39, Mn =55, O = 16 ] Page 2 of 8

3 2. A group of students prepared ethanal (CH 3 CHO) by slowly adding an aqueous solution of ethanol ( H 5 OH) and sodium dichromate(vi) (Na 2 Cr 2 O 7.2H 2 O) to a hot aqueous solution of sulfuric acid (H 2 SO 4 ). The reaction is described by the following equation. 3 H 5 OH + Cr 2 O H + 3CH 3 CHO + 2Cr H 2 O The apparatus drawn below was used. (c) (e) State and explain two features of the preparation that are necessary to ensure the yield of ethanal is maximised. (8) The ethanol/oxidising agent mixture was added slowly to the hot acid; explain why this was necessary. (6) State and explain the colour change that is observed during the addition of the ethanol and sodium dichromate(vi) solution to the hot acid. (9) Describe how you would carry out the silver mirror test on a sample of ethanal. (12) If the students used 7.45 g of sodium dichromate(vi) (Na 2 Cr 2 O 7.2H 2 O) and they collected 2.4 cm 3 of ethanal (density 0.78g/cm 3 ), in this experiment what was their % yield? (15) [ Relative atomic masses: H = 1, C = 12, O = 16, Na = 23, Cr = 52 ] 3. Hydrogen peroxide decomposes rapidly in the presence of a manganese(iv) oxide (MnO 2 ) catalyst. Write a balanced equation for the decomposition of hydrogen peroxide. (5) Draw a labelled diagram of an apparatus a student could assemble to measure the rate of decomposition of hydrogen peroxide in the presence of a manganese(iv) oxide (MnO 2 ) catalyst. Indicate clearly how the reaction could be started at a time known exactly, and how the gas produced is collected and its volume measured. (12) The table shows the volumes of gas (at room temperature and pressure) produced at intervals over 10 minutes. Time (min) Volume of O 2 (cm 3 ) (c) Plot a graph to illustrate the volume of oxygen produced versus time. (12) Use the graph to determine (i) the percentage of oxygen produced after 2.5 minutes, (ii) the total mass of oxygen gas produced in this experiment and (iii) the instantaneous rate of the reaction after 3 minutes. (15) (e) Explain why the rate of the reaction gets slower as the reaction proceeds. (6) Page 3 of 8

4 Section B [See page 1 for instructions regarding the number of questions to be answered.] 4. Answer eight of the following items,, (c), etc. (50) (c) Distinguish between (i) sigma and (ii) pi (π) covalent bonding. What are alpha particles? What happens during secondary sewage treatment? Define relative atomic mass. (e) What are the possible shapes for molecules of general formula AB 3? (f) (g) (h) What is meant by homogeneous catalysis? Draw an energy profile diagram of an endothermic reaction and indicate on the diagram the activation energy. What are mercaptans? (i) What is the oxidation number of sulfur in (i) Na 2 S 2 O 3 and (ii) H 2 SO 3 (j) Write the (i) conjugate acid and (ii) the conjugate base of H 2 PO 4. (k) Answer part A or part B. A B How does nitrogen fixation occur in nature? or Give an example of (i) an ionic crystal and (ii) a covalent macromolecular crystal. 5. Define energy level. (3) What contribution did Newlands make to the systematic arrangement of the elements? (6) State two ways in which Mendeleev s periodic table of elements differs from that of Moseley. (6) The diagram shows how the lines in the hydrogen emission spectra are related to energy levels. Explain how line emission spectra occur. (9) Why is it possible for line emission spectra to be used to distinguish between different elements? (3) (c) Define fi rst ionization energy. (5) Account fully for the trends in first ionisation energies of elements across the second period of the periodic table (i.e. Li to Ne). (12) Account for the trend in first ionisation energies of the elements going down Group II of the periodic table, i.e. the alkaline-earth metals. (6) n = 6 n = 5 n = 4 n = 3 n = 2 n = 1 purple blue/green red nucleus Page 4 of 8

5 6. Define heat of combustion. (5) The combustion of 2,2,4-trimethyl pentane may be described by the following balanced equation: 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O (l) ΔH = 10,934 kj mol 1 Given that the heats of combustion of carbon and hydrogen are 394 and 286 kj mol 1, respectively, calculate the heat of formation of 2,2,4-trimethyl pentane. (15) What is the octane number of a fuel? (6) Name both the reference hydrocarbons used in measuring the octane number of a fuel. (6) State two structural features of a hydrocarbon which contribute to it having a high octane number. (6) (c) What is catalytic cracking? (6) Upon cracking, a molecule of C 15 H 32 produces propene C 3 H 6, octane C 8 H 18 and a four carbon alkene molecule. Draw the three isomers of the alkene and give their systematic IUPAC names. (6) 7. State Le Châtelier s principle. (5) The formation of ammonia from its elements is shown in the following reversible reaction. This is an important process in the fertilizer industry. N 2 (g) + 3H 2 (g) 2NH 3 (g) H = 92.4 kj mol 1 What is the name given to this industrial process? (3) (c) Write the equilibrium constant expression (K c ) for the reaction above. (6) In an experiment seven moles of nitrogen and 21 moles of hydrogen were mixed in a 12 litre vessel at a certain temperature. It was found that there was eight moles of ammonia in the equilibrium mixture. Calculate the concentration of each gas at equilibrium in moles/litre. Calculate the value of the equilibrium constant (K c ) at this temperature. (15) (e) Name the catalyst used in this reaction. (3) (f) State and explain the ideal conditions of temperature and pressure needed to maximise the yield of ammonia. (12) (g) What conditions are actually used? Explain the reason for each. (6) Page 5 of 8

6 8. Define (i) an acid, (ii) a base according to the Brønsted-Lowry theory. (6) Identify one species acting as a base, and also identify its conjugate acid in the following system: (6) H 2 S + O 2 OH + SH Define ph. (5) A bottle of vinegar is labelled 5% (w/v) acetic acid (ethanoic acid). The dissociation constant, K a, for ethanoic acid is Calculate the approximate ph of the vinegar solution. (12) Find the concentration of a nitric acid (HNO 3 ) solution which has the same ph. (3) (c) What is meant by the biochemical oxygen demand (BOD) of a water sample? (6) cm 3 of water from a stream was diluted to one litre with distilled water and then divided into two portions. The dissolved oxygen concentration of one of the portions was measured immediately and was found to be 9.6 p.p.m. After storing the other portion for a period of time and under certain conditions for the determination of BOD the dissolved oxygen concentration was found to be 2.2 p.p.m. (i) For how long and under what conditions was the second portion stored? (6) (ii) Calculate the BOD of the undiluted stream water. (6) 9. (A) (B) (C) (D) H 5 OH X H 4 Y H 6 Z H 5 Cl W H 4 Br 2 (E) Give the systematic (IUPAC) names of A, B, C, D and E. (5) (c) For each of the conversions labeled W, X, Y and Z, classify it as an addition, a substitution or an elimination reaction. (12) The conversion labelled Z is known to occur by a free radical mechanism. State three clear pieces of experimental evidence that support this mechanism. (15) Name the reagent and catalyst required to convert B to C. (6) (e) (f) After carrying out the laboratory conversion of A to B, how would you test the product to confirm the formation of B? (6) Compound A can be oxidised under reflux to give a two carbon acid. What is the name of this acid? Name the flavouring agent that contains this acid at a concentration of 6% w/v. (6) Page 6 of 8

(4) What observations would be made in this test? (9) What is a catalyst? (4) Modern cars now have catalytic converters built into their engines.

7 10. Answer any two of the parts, and (c). (2 25) Describe a test which could be carried out to identify the presence of the nitrate ion in aqueous solution. (12) What test could be carried out to distinguish between the three nitrate salts barium nitrate (Ba(NO 3 ) 2 ), potassium nitrate (KNO 3 ) and sodium nitrate (NaNO 3 )? (4) What observations would be made in this test? (9) What is a catalyst? (4) Modern cars now have catalytic converters built into their engines. Name one element used as a catalyst in a catalytic converter. (3) State and explain the effect leaded petrol would have on a catalytic converter. (6) Name the two theories of catalysis. (6) State which of these theories occur in the catalytic converter in a car. (6) (c) State Boyle s law. (6) Define an ideal gas and state one way in which steam deviates from ideal gas behaviour. (7) In an experiment a small quantity of the volatile organic compound propanone (CH 3 CO CH 3 ) was evaporated at room temperature and pressure. Use the equation of state for an ideal gas to calculate the volume, in litres, of propanone vapour formed when 0.29 g of liquid propanone evaporates, taking room temperature as 20ºC and room pressure as 101 kpa. [ Use molar volume at room temperature and pressure = 24.0 litres ] (12) Page 7 of 8

11. Answer any two of the parts, and (c). (2 25) The following reaction is used in the formation of nitrogen monoxide. 3Cu(s) + 8 HNO 3 (aq) 3Cu(NO 3 ) 2 (aq) + 2 NO(g) + 4H 2 O(aq) 100 cm 3 of 2.

(6) (iii) How many water molecules were produced if there is only a 75% yield of all products? (9) [ Relative atomic masses: Cu = 63.5 ] Explain reduction in terms of electron transfer.

8 11. Answer any two of the parts, and (c). (2 25) The following reaction is used in the formation of nitrogen monoxide. 3Cu(s) + 8 HNO 3 (aq) 3Cu(NO 3 ) 2 (aq) + 2 NO(g) + 4H 2 O(aq) 100 cm 3 of 2.0 M solution of nitric acid was reacted with 6.0g of copper. (i) Show clearly that the copper is in excess in this reaction. (10) (ii) What volume of nitrogen monoxide measured at s.t.p. was produced? (6) (iii) How many water molecules were produced if there is only a 75% yield of all products? (9) [ Relative atomic masses: Cu = 63.5 ] Explain reduction in terms of electron transfer. (4) Explain the term electrolysis. (3) A solution of potassium iodide was electrolysed using the apparatus shown here. Write the balanced half equations for the reactions that occur at the anode and the cathode. (12) Phenolphthalein was added to the solution at the start of the experiment; describe the colour change that occurs at each electrode. (6) (c) Answer part A or part B. A Explain the terms (i) greenhouse gas and (ii) an acidic oxide. (7) State two major ways by which human activities contribute to the addition of carbon dioxide to the atmosphere. (6) Carbon dioxide is removed from the atmosphere when it dissolves in rainwater, in seas, in lakes, etc. What three chemical species form as a result of carbon dioxide gas dissolving in water? (9) Acidic oxides can be removed from waste gases by scrubbers in chimneys before the gases are released into the atmosphere. Name a reagent used in scrubbers to remove acidic oxides. (3) or B (i) Identify the monomer used to manufacture poly (phenylethene). (4) (ii) What type of polymerisation reaction occurs in the manufacture of poly (phenylethene). (3) (iii) Draw two repeating units of the poly (phenylethene) polymer. (6) (iv) Give two properties of poly (phenylethene). In the case of each property you have stated, give a major use of the polymer that involves use of that property. (12) Page 8 of 8

CHEMISTRY HIGHER LEVEL

*P15* PRE-LEAVING CERTIFICATE EXAMINATION, 2008 CHEMISTRY HIGHER LEVEL TIME: 3 HOURS 400 MARKS Answer eight questions in all These must include at least two questions from Section A All questions carry