Structured questions1a)Hazard warning labels are often found on bottles containing chemicals.State the hazardous nature of each chemical shown above.ii)Give ONE precaution you should take when handling each of the chemicals.b)The diagram below shows a student heating a mixture of solids to prepare ammonia gas.He is trying to detect the smell of ammonia.State TWO inappropriate laboratory practices of the student and suggest the properactions that should be taken. (8 marks)Answer:1a)i)Chemical A - flammable (1)Chemcial B - corrosive(1)ii)Chemical A - do not use naked flame.(1)Chemical B - wear safety glasses and protective gloves.(1)b)The student does not have eye protection.(1)He should wear safety glasses.(1)The student should not detect the smell of ammonia while heating the reactionmixture. The mixture may shoot at his face.(1)Detect ammonia with testing paper / testing agent.(1)2X is the most abundant element in air. Air also contains oxygen and other substances.a)Identify element X.b)Is oxygen an element or a compound? Explain briefly.c)What is the most abundant compound in air?d)Both oxygen and element X can be obtained by the fractional distillation of liquid air.i)Where does the fractional distillation of liquid air take place in industry?ii)Explain briefly why oxygen and element X can be obtained by the fractionaldistillation of liquid air.iii)Does the fractional distillation of liquid air involve a physical or chemical change?Explain briefly.e)Suggest a test which allows you to distinguish between oxygen and element X.f)Suggest a test to identify the compound suggested in (c).g)State the hazard warning label that should be displayed on a jar containing oxygen.(13 marks)Answer:2a)Nitrogen(1)b)It is an element.(1)It cannot be broken down into anything simpler by chemical methods.(1)c)Carbon dioxide(1)d)i)Fractionating column(1)ii)They have different boiling points.(1)iii)It involves a physical change.(1)No new substance is formed in the process.(1)e)Test with a glowing splint.(1)Oxygen relights the glowing splint.(1)Element X (nitrogen) extinguishes the glowing splint.(1)f)It turns limewater milky.(1)g)Oxidizing(1)Consider the following substances:Sodium chloride, water, nitrogen, carbon dioxide, oxygen, argona)Classify the above substances into elements and compounds.b)Suggest a test for each of the following species:i)oxygen;ii)sodium in sodium chloride;iii)chloride in sodium chloride;iv)water.c)The table below gives some information of certain components in a sample of liquefiedair.CompoundBoiling point (oC)Argon-186Nitrogen-196Oxygen-183In what order are these components distilled out when the liquefied air undergoesfractional distillation? Explain your answer. (14 marks)Answer:3a)Elements: nitrogen, oxygen, argon(2)Compounds: sodium chloride, water, carbon dioxide (2)b)i)Oxygen relights a glowing splint.(1)ii)Test for sodium: sodium gives a golden yellow flame in flame test. (1, 1)iii)Test for chloride: when diluted nitric acid followed by silver nitrate solution areadded to sodium chloride solution, a white precipitate is formed. (1, 1)iv)Water turns dry cobalt(II) chloride paper from blue to pink. (1, 1)c)The order is nitrogen, argon and then oxygen.(1)In fractional distillation, a component with a lower boiling point will be distilled out first.The boiling point of the components is in the order of nitrogen < argon < oxygen.Therefore, nitrogen is distilled out first, followed by argon and then oxygen.(2)4Some ice cream and ice cubes were taken out from a freezer at the same time and allowed tostand in the air. Their temperatures were recorded every minute until both had meltedcompletely. The results are given in the table.Time (minute)Temperature of ice cream (oC)Temperature of ice(oC)0-12-121-10-62-8-33-7-14-605-5.506-507-4.508-409-3.5010-3011-2.5012-2013-101400152016411764a)Draw curves for both sets of results on the same graph.b)According to the graph in (a), determinei)the period of time in which the ice was melting; andii)the time at which both ice cubes and ice cream had melted completely.c)Is ice cream a mixture or a compound? d)Ice is the solid state of water.i)Suggest an experiment to prove that water is a compound.ii)Suggest a test to show the presence of water in ice.(9 marks)Answer:4a)(2)b)i)Between 4th and 15th minute(1)ii)16th minute(1)c)Ice cream is a mixture.(1)d)i)Electrolysis of water(1)produces hydrogen and oxygen.(1)ii)Water can turn dry cobalt(II) chloride paper(1)from blue to pink.(1)5The following is a sample of sea water collected by a student from a beach.a)Explain whether the sample is a mixture, an element or a compound.b)i)Suggest a method for removing the sand and mud from the sample.ii)Draw a labelled diagram of the experimental set-up for the separation methodsuggested in (i).c)i)Suggest a method for obtaining solid sodium chloride from the sample of sea water.ii)Draw a labelled diagram of the experimental set-up for the separation method suggested in (i).iii)Describe how you can show the presence of chloride in the solid sodium chlorideobtained.iv)Suggest ONE daily use of sodium chloride.(13 marks)Answer:5a)The sample is a mixture of water, sodium chloride, sand and mud.(1)Substances in the sample of sea water are not chemically joined together.(1)b)i)By filtration(1)ii)(1 mark for correct set-up; 1 mark for labelling filter funnel and filter paper;1 mark for labelling residue and filtrate; award 0 mark if the set-up is not workable)(3)c)i)By evaporation(1)ii)(1 mark for correct set-up; 1 mark for labelling evaporating dish; award 0 markif the set-up is not workable)(2)iii)Dissolve the solid sodium chloride in water.(1)Add dilute nitric acid, followed by silver nitrate solution to the sodium chloride solution.(1)A white precipitate is formed.(1)iv)As table salt / preservative / flavouring agent(1)6Consider the following flowchart. a)i)Name the physical change shown above.ii)What might solid X be?iii)Suggest ONE use of solid X.iv)Name a process for obtaining pure solid X from sea water.b)i)Name the chemical change shown above.ii)Draw a labelled diagram of the experimental set-up for conducting the abovechemical change in the laboratory.c)i)Suggest what gas Y might be.ii)State ONE use of chlorine gas and gas Y respectively.(11 marks)Answer:6a)i)Evaporation(1)ii)Sodium chloride(1)iii)As preservative / flavouring agent(1)iv)Crystallization(1)b)i)Electrolysis(1)ii)(1 mark for correct labels of two electrodes; 1 mark for correct collection method forgaseous products at electrodes; 1 mark for correct labels of products; award 0 mark if theset-up is not workable)(3)c)i)Hydrogen(1)ii)Chlorine: sterilizing drinking water / sterilizing swimming pool water / manufactureof PVC and organic solvents / manufacture of hydrochloric acid / manufacture ofbleach(1)Gas Y: manufacture of ammonia / as rocket fuel / manufacture of hydrochloric acid(1)A colourless solid melts at 0 oC and becomes a liquid at room temperature and pressure. Whenthe liquid undergoes electrolysis, two colourless gases are formed.a)Identify the physical and chemical change in the above description.b)i)From the above description, give ONE evidence that the liquid is water.ii)Suggest a chemical test to show that the liquid is water.c)i)Identify the TWO gases formed during electrolysis.ii)Suggest tests to identify these two gases. (9 marks)Answer:7a)Physical change: solid melts to become liquid.(1)Chemical change: liquid undergoes electrolysis to form two gases.(1)b)i)The solid melts at 0 oC at room temperature and pressure. (melting point of water = 0 oC)(1)ii)Water can turn dry cobalt(II) chloride paper from blue to pink. (1, 1)c)i)Hydrogen and oxygen (1, 1)ii)Hydrogen gives a pop sound with a burning splint.(1)Oxygen can relight a glowing splint.(1)8The results of three tests for substances A and B are summarized in the following table:SubstanceTest 1:Flame testTest 2:Addition of acidified silver nitrate solution to solution of substanceTest 3:Addition of dilute hydrochloric acidAGolden yellow flameA white precipitate is formedNo observable changeBBrick-red flameInsoluble in waterA gas which can turn limewater milky is evolveda)According to the results of Test 1, what are present in A and B respectively?b)According to the results of Tests 2 and 3, explain briefly what are present in A and Brespectively. c)Name substances A and B. d)State ONE source of substances A and B respectively. e)What will happen ifi)A is heated strongly?ii)B is heated strongly? (12 marks)Answer:8a)A: Sodium(1)B: Calcium(1)b)A: Chloride (ions) (1)Solution of A gives a white precipitate (silver chloride) in the silver nitrate test.(1)B: Carbonate (ions)(1)B reacts with dilute hydrochloric acid to produce carbon dioxide which turns limewatermilky.(1)c)A: Sodium chloride(1)B: Calcium carbonate(1)d)A: Sea water(1)B: Limestone / marble / chalk(1)e)i)No reaction(1)ii)Calcium carbonate decomposes on heating to give calcium oxide and carbondioxide.(1)9The above set-up is used to collect the liquid given off when copper(II) sulphate crystals areheated. Tube X is held in position using stands and clamps.a)At which position along tube X should it be clamped? Explain your answer.b)Why should tube X be clamped in a slanting position as shown above?c)Why is the free end of the delivery tube kept above the liquid collected in tube Y?d)Why is tube Y put in a beaker containing ice and cold water?e)Suggest a test to show that the liquid collected in tube Y is water.f)What would be the colour change of the crystals in tube X upon heating?g)Decide whether the copper(II) sulphate crystals undergo a chemical change or physicalchange in this experiment.(9 marks)Answer:9a)Tube X should be clamped near to the stopper(1)to avoid burning of the rubber lining of the clamp.(1)b)To prevent water condensed at the mouth of the tube from flowing back to the hotter partof the tube and thus cracking it.(1)c)To prevent liquid sucking back from tube Y.(1)d)To condense the vapour given off.(1)e)Water turns dry cobalt(II) chloride paper from blue to pink. (1, 1)f)From blue to white.(1)g)A chemical change.(1)10In the manufacture of beer, brewers often add small amounts of calcium sulphate andmagnesium sulphate to the water used. These chemicals influence the chemical reaction duringthe brewing process.a)Flame test can be used to show that a solid sample contains calcium.i)Describe how you would carry out a flame test.ii)State the colour of the flame you expect to observe if the sample under test containscalcium.iii)Impurities may lead to other colours being observed in the flame. What species islikely to be present if a yellow flame is seen?b)Describe a test you would carry out to show that a solid sample contains sulphate. Statealso the expected observation.(8 marks)Answer:10a)i)Dip a clean nichrome wire into concentrated hydrochloric acid.(1)Dip the nichrome wire into the sample.(1)Heat the wire in a Bunsen flame.(1)ii)A brick-red flame(1)iii)Sodium(1)b)Dissolve the sample in water. Add dilute hydrochloric acid followed by barium chloridesolution to the solution. (1, 1)A white precipitate shows that the sample contains sulphate.(1)11Consider three substances: chalk, limestone and marble.a)i)What is the common substance present in chalk, limestone and marble?ii)Suggest chemical tests to show the presence of this substance in limestone.b)Which substance is the hardest among chalk, limestone and marble?c)State the conditions for the conversion of limestone to marble.d)Suggest ONE use of limestone.e)A chalk is heated strongly.i)What will happen if chalk is heated strongly?ii)Water is added to the solid remained after heating. Solution Y is formed.(1)Write a word equation for the reaction.(2)State ONE use of solution Y.f)State TWO observable changes when a piece of chalk is added into dilute hydrochloricacid? Write a word equation for the reaction.(15 marks)Answer:11a)i)Calcium carbonate(1)ii)Calcium (ions)Give a brick-red flame in flame test (1, 1)Carbonate (ions)Add dilute hydrochloric acid to limestone,(1)a gas which turns limewater milky is evolved.(1)b)Marble is the hardest.(1)c)Limestone changes to marble under high pressure and high temperature. (1, 1)d)Making cement / glass / materials for construction / to neutralize acidity in soil and water(1)e)i)Chalk (calcium carbonate) will decompose to give calcium oxide and carbon dioxide.(1)ii)(1)Calcium oxide + water calcium hydroxide(1)(2)As limewater(1)f)The chalk dissolves.(1)Gas bubbles evolve (effervescence).(1)Calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide(1)12The following diagram shows some natural processes in our environment. a)What is Process 1?b)Classify processes 1, 2 and 3 into physical change(s) and chemical change(s).c)Explain briefly how rainwater causes the erosion of limestone. d)i)What is the main substance left after a sample of sea water is evaporated to dryness?ii)Suggest TWO uses of this substance in our daily lives.e)Pure water can be obtained from distillation of sea water.i)Does distillation of sea water involve a physical or chemical change?ii)Draw a labelled diagram of the experimental set-up for simple distillation of seawater.(13 marks)Answer:12a)Evaporation of sea water (water)(1)b)Process 1: Physical change(1)Process 2: Physical change(1)Process 3: Physical change and chemical change(1)c)Carbon dioxide in the air dissolves in water to form carbonic acid.(1)Carbonic acid reacts with calcium carbonate to form soluble calcium hydrogencarbonatewhich is washed away readily.(1)d)i)Table salt / sodium chloride(1)ii)As preservative and flavouring agent (1, 1)e)i)It involves a physical change.(1)ii)(1 mark for correct set-up; 1 mark for labelling anti-bumping granules andthermometer; 1 mark for labelling sea water and pure water; award 0 mark if theset-up is not workable)(3)13A student carried out an experiment on thermal decomposition of limestone.a)i)What is the major constituent of limestone?ii)Name a natural occurring substance with the same major constituent as limestone. b)Write a word equation for the thermal decomposition of limestone.c)A gas is evolved during the thermal decomposition of limestone.i)Draw a labelled diagram of an experimental set-up for heating the limestone andtesting the gas evolved.ii)State any observable change for the test of the gas evolved. Write a word equationfor the change involved. d)Describe briefly how you can show the presence of calcium in limestone.(11 marks)Answer:13a)i)Calcium carbonate / CaCO3(1)ii)Chalk / marble(1)heatb)Calcium carbonate calcium oxide + carbon dioxide(1)c)i)(2)ii)The limewater turns milky.(1)Calcium hydroxide + carbon dioxide calcium carbonate + water(1)d)Dip a clean nichrome wire into concentrated hydrochloric acid.(1)Dip the nichrome wire into powdered limestone.(1)Heat the wire in a Bunsen flame.(1)A brick-red flame is observed.(1)14Answer this question with reference to the diagram below:a)Name substances A, B and C.b)What should process X be? c)Write a word equation fori)the decomposition of substance A on strong heating; andii)addition of dilute hydrochloric acid to substance A.d)Carbon dioxide is bubbled into substance C. What will be observed? Write a wordequation for the reaction involved.e)A student wants to obtain pure calcium chloride crystals from a calcium chloride solution.i)Describe briefly how he can obtain the crystals from the solution.ii)The student cannot distinguish between sodium chloride crystals and calcium chloride crystals. Suggest a test that allows him to distinguish them.(14 marks)Answer:14a)A: Calcium carbonate(1)B: Calcium oxide(1)C: Limewater / calcium hydroxide solution(1)b)Addition of water(1)heatc)i)Calcium carbonate calcium oxide + carbon dioxide(1)ii)Calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide(1)d)Limewater (substance C) turns milky.(1)Calcium hydroxide + carbon dioxide calcium carbonate + water(1)e)i)Heat the solution until a saturated solution is obtained.(1)Cool the solution slowly until large crystals are obtained.(1)Filter off the crystals and wash the crystals with a small amount of cold water. Dry them with filter paper.(1)ii)Flame test(1)Sodium chloride gives a golden yellow flame(1)Calcium chloride gives a brick-red flame.(1)15Describe briefly, using the following apparatus and materials, how you can distinguishhydrated calcium chloride crystals, calcium oxide and calcium carbonate.Test tubes, a test tube holder, a Bunsen burner, limewater, dry cobalt(II) chloride papers,delivery tubes(You are required to give a paragraph-length answer. In this question, 6 marks will be awardedfor chemical knowledge and 3 marks for effective communication.)(9 marks)Answer:15Heat these three substances in test tubes separately.(1)Then place a piece of dry cobalt(II) chloride paper near to the mouth of each test tube.(1)Only hydrated calcium chloride crystals turn the paper from blue to pink as water ofcrystallization is given off upon heating.(1)Then detect any gas evolved with limewater.(1)Only calcium carbonate gives a gas which turns limewater milky as calcium carbonatedecomposes on heating to give carbon dioxide.(1)The remaining solid is thus calcium oxide which is stable on strong heating.(1)(3 marks for effective communication)16Suppose you are provided with a mixture of impure sodium chloride powder and sand.Describe how you can obtain pure sodium chloride crystals from the mixture.(You are required to give a paragraph-length answer. In this question, 6 marks will be awardedfor chemical knowledge and 3 marks for effective communication.)(9 marks)Answer:16Dissolve the mixture in distilled water.(1)Remove the insoluble impurities and sand from the solution by filtration.(1)Heat the filtrate until a saturated solution is obtained.(1)Cool the solution slowly to obtain large sodium chloride crystals.(1)Filter off the crystals.(1)Wash the crystals with a small amount of cold water and dry them with filter paper.(1)(3 marks for effective communication)