2021 ACSI Prelims Paper 2

1 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over Anglo-Chinese School (Independent) Year 4 Express Preliminary Examination 2021 CHEMISTRY PAPER 2 6092/2 Tuesday 17th August 2021 1 hour 45 minutes Additional materials: Calculator INSTRUCTIONS TO CANDIDATES Write your candidate number in the box at the top of this page and on any separate answer paper used. Section A Answer all questions in the spaces provided. Section B Answer all three questions in the spaces provided. The last question is in the form of EITHER / OR and only one alternative should be attempted. At the end of the examination, hand up the paper in one bundle. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 23. You may use a calculator. This question paper consists of 23 printed pages. Candidate Number FOR EXAMINER’S USE Section A B9 B10 B11 significant figures units TOTAL

2 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over Section A Answer all questions in the spaces provided. The total mark for this section is 50. A1 The diagram shows part of the Periodic Table. Use the letters S-Z to answer the questions below. S-Z does not represent the symbols of the actual elements. Z U X T V S W Y (a) Which element exists as a solid at r.t.p, has low density and floats on water? [1] (b) Which element shows both metallic and non-metallic character? [1] (c) Which elements are transition elements? [1] (d) State two characteristic properties of transition elements. [2] (e) Which gaseous element is likely to remain as a monoatomic substance? [1]

3 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over A2 The reaction between nitrogen and hydrogen to form ammonia is a reversible reaction as shown below. forward reaction : N2 (g) + 3H2 (g) → 2NH3 (g) ∆H = - 92 kJ/mol backward reaction : 2NH3 (g) → N2 (g) + 3H2 (g) ∆H = + 92 kJ/mol In order to determine the most cost-effective way to produce ammonia, a chemist Fritz Haber did a series of experiments to determine the yield of ammonia at different conditions. temperature / oC pressure / atm 300 400 500 400 48% NH3 55% NH3 61% NH3 500 26% NH3 32% NH3 38% NH3 600 13% NH3 17% NH3 21% NH3 (a) Using the information given, state the conditions needed to produce the highest yield of ammonia. [1] (b) Explain why the Haber Process is carried out at only 250 atm. [1] (c) Suggest a possible explanation why it is ideal to remove ammonia as quickly as possible after it is formed. [1]

4 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over A3 An element M with a relative atomic mass of 152.4 exist in three isotopic forms as shown below. isotope 150M 155M 157M isotopic abundance 60 % X % Y % (a) Define isotopes. [2] (b) Determine, using calculations, the values of X and Y. [2] (c) Given that 40Ar, 40K and 40Ca are isobars. Using the information provided, explain what isobars are. [1]

5 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over A4 Aldehyde is a homologous series that contains the CHO functional group. Aldehydes can be obtained through the controlled oxidation of alcohols. More information about the aldehyde homologous series can be seen in the table below. name of aldehyde condensed formula displayed formula boiling point / oC methanal HCHO - 19 ethanal CH3CHO 20 propanal C2H5CHO 49 butanal C3H7CHO 75 (a) Draw the displayed formula of propanal in the table above. [1] (b) Write the general formula of the aldehyde homologous series. [1] (c) Pentanal is a five-carbon aldehyde. Predict the boiling point of pentanal. [1]

6 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over (d) Butanal has a molecular formula of C4H8O. It can exist as several isomers. (i) Explain what isomers are. [1] (ii) Draw the displayed formula of an isomer of butanal. [1] (e) Explain why the boiling point of aldehydes increases down the homologous series. [2]

7 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over (f) Hydroformylation is an industrial process to produce aldehydes from alkenes. This chemical reaction involves the addition of carbon monoxide gas and hydrogen gas at a temperature of 120 oC and a pressure of 40 atm. An example of the hydroformylation can be seen below. + CO + H2 ⇌ propene butanal Styrene is the monomer used to produce polystyrene which is commonly used in foam food packaging. The structure of styrene is shown below. (i) Styrene also undergoes hydroformylation. Draw the displayed formula of the product formed as a result. [1] (ii) The product formed in (f)(i) is further oxidized to form compound X. compound X is able to react with magnesium to form a gas. Draw the structure of compound X. [1]

8 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over A5 The following gases are found in the atmosphere and they have different effects on the environment. A carbon dioxide B carbon monoxide C chlorofluorocarbon D chlorine monoxide E nitrogen dioxide F oxygen (a) Use the letters A to F to answer the following questions. (i) Which two gases combine together to form a substance responsible for global warming? [1] (ii) Which gaseous pollutants, produced in the internal combustion engine of a car, are removed effectively by the catalytic converter? [1] (iii) Which gases are responsible for the formation of acid rain? [1] (b) A particular chlorofluorocarbon contains 41.5% by mass of chlorine and 44.4% by mass of fluorine. Given that the molar mass is 171 g/mol, determine the empirical formula and molecular formula of chlorofluorocarbon. [3]

9 Anglo-Chinese School (Independent) 6092/2 Year 4 Express Preliminary Exam 2021 [Turn over (c) The destruction of the ozone layer by chlorofluorocarbon takes place via a three - step mechanism. Step 1 involves the breaking of the covalent bond between a carbon atom and chlorine atom in a chlorofluorocarbon in the presence of ultraviolet light. The equ ation below shows step 1 of the mechanism involving the chlorofluorocarbon CCl2F2. Step 1 : CCl2F2 → CClF2 + Cl Step 2 of the mechanism involves the chlorine atom formed from a chlorofluorocarbon attacking an ozone molecule to form chlorine monoxide and oxygen gas. This is shown in the equation below. Step 2 : Cl + O3 → ClO + O2 In the third step, the chlorine monoxide molecule produced reacts with an ozone molecule to produce oxygen gas and a chlorine atom. (i) Construct a balanced chemical equation for this reaction. [1] (ii) Using your answer in (c)(i) and the second step of the mechanism, explain why one chlori