21 st Century Chemistry Structured Question in Topic 1 Planet Earth Unit 1-4

Transcription

1 21 st Century Chemistry Structured Question in Topic 1 Planet Earth Unit Air consists of oxygen and other substances. (a) Is oxygen an element or a compound? Explain briefly. It is an element. [1] It cannot be broken down into anything simpler by chemical method. [1] (b) (i) What is the most abundant element in air? Nitrogen [1] (ii) What is the most abundant compound in air? Carbon dioxide [1] (c) Both oxygen and the element in (b)(i) can be obtained by fractional distillation of liquid air. (i) Where does fractional distillation of liquid air take place in industry? Fractionating column [1] (ii) Explain briefly why oxygen and the element in (b)(i) can be obtained by fractional distillation of liquid air. They have different boiling points. [1] (iii) Does fractional distillation of liquid air involve physical or chemical change? Explain briefly. It involves physical change. [1] No new substance is formed in the process. [1] (d) Suggest a test which allows you to distinguish between oxygen and the element in (b)(i). Test with a glowing splint. [1] Oxygen relights the glowing splint. [1] The element in (b)(i) (nitrogen) extinguishes the glowing splint. [1] (e) Suggest a test to identify the compound in (b)(ii). It turns limewater milky. [1] (f) State the hazard warning label that should be displayed on a jar containing oxygen. Oxidizing [1] (13 marks)

2 2. Consider the following substances: Sodium chloride, water, nitrogen, carbon dioxide, oxygen, argon (a) Classify the above substances into elements and compounds. Element: nitrogen, oxygen, argon [2] Compound: sodium chloride, water, carbon dioxide [2] (b) (i) Which of the above substances can be obtained from air industrially? Nitrogen, oxygen and argon [2] (ii) Give the name of the industrial method. Fractional distillation of liquid air [1] (c) Suggest chemical test(s) for (i) oxygen; Oxygen relights a glowing splint. [1] (ii) sodium chloride; and Test for sodium: sodium gives golden yellow flame in flame test. [1, 1] Test for chloride: sodium chloride solution gives white precipitate [1] with dilute nitric acid, followed by silver nitrate solution. [1] (iii) water. Water turns dry cobalt(ii) chloride paper from blue to pink. [1, 1] (14 marks)

3 3. Some ice cream and ice cubes were taken out from a freezer at the same time and allowed to stand in air. The temperature was recorded respectively every minute until both had completely melted. The results are given in the table. Time/minute Temperature of ice cream/ Temperature of ice/ (a) Draw curves for both sets of results on the same graph. (b) According to the graph, determine (i) the period of time in which the ice was melting; and [2]

4 (c) (d) Between 4th and 15th minute [1] (ii) the time when both ice cubes and ice cream were completely melted. 16th minute [1] Is ice cream a mixture or a compound? Ice cream is a mixture. [1] Ice is the solid state of water. (i) Suggest an experiment which can prove that water is a compound. Electrolysis of water [1] produces hydrogen and oxygen. [1] (ii) Suggest a test to show the presence of water in ice. Water can turn dry cobalt(ii) chloride paper [1] from blue to pink. [1] (9 marks)

5 4. The 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. The sample is a mixture of water, sodium chloride, sand and mud. [1] The substances in the sample of sea water are not chemically joined together. [1] (b) (i) Suggest how sand and mud can be removed from the sample. By filtration [1] (ii) Draw the experimental set-up for the separation in (b)(i). (1 mark for the diagram; 1 mark for labelling funnel and filter paper; 1 mark for labelling residue and filtrate) [3] (c) (i) State how sodium chloride powder can be obtained from the sample of sea water. By evaporation [1] (ii) Draw the experimental set-up for (c)(i). (iii) (1 mark for the diagram; 1 mark for labelling evaporating dish) [2] Describe how we can show the presence of chloride in the sodium chloride powder obtained.

6 (iv) Dissolve the sodium chloride powder in water. [1] Add dilute nitric acid, followed by silver nitrate solution to the sodium chloride solution. [1] White precipitate is formed. [1] Suggest a daily use of sodium chloride. As table salt/ preservative / favouring agent [1] (13 marks)

7 5. Consider the following flowchart. (a) (i) Suggest the physical process shown above. Evaporation [1] (ii) What might solid X be? Sodium chloride [1] (iii) Suggest a use of solid X. As preservative/ flavouring agent [1] (iv) Name the physical process in which pure solid X can be obtained from sea water. Crystallization [1] (b) (i) Suggest the chemical process shown above. Electrolysis [1] (ii) Draw a labelled diagram of the experimental set-up for the above chemical process in the laboratory. (1 mark for labelling the two electrodes; 1 mark for showing the collection of gaseous products at the electrodes; 1 mark for labelling the correct products.) [3] (c) (i) Suggest what gas Y might be. Hydrogen [1] (ii) State one common use of chlorine gas and gas Y respectively. Chlorine: sterilizing drinking water/ sterilizing swimming pool water/ manufacture of PVC and organic solvents/ manufacture of hydrochloric acid/ manufacture of bleach [1] Gas Y: manufacture of ammonia/ as rocket fuel/ manufacture of hydrochloric acid [1] (11 marks)

8 6. A colourless solid melts at 0 and becomes a liquid at room temperature and pressure. When the liquid undergoes electrolysis, two colourless gases are formed. (a) Identify the physical and chemical change from the above description. Physical change: solid melts to become liquid. [1] Chemical change: liquid undergoes electrolysis to form two gases. [1] (b) (i) From the above description, give one evidence that the liquid is water. The solid melts at 0 at room temperature and pressure. (melting point of water = 0 ) [1] (ii) Suggest a chemical test to show that the liquid is water. Water can turn dry cobalt(ii) chloride paper from blue to pink. [1, 1] (c) (i) Identify the two gases formed during electrolysis. Hydrogen and oxygen [1, 1] (ii) Suggest tests to identify these two gases. Hydrogen gives a 'pop' sound with a burning splint. [1] Oxygen can relight a glowing splint. [1] (9 marks)

9 7. The results of tests 1-3 with substances A and B are summarized in the following table: Test 1: Flame test (a) Substance Test 2: Addition of dilute nitric acid, followed by silver nitrate solution Test 3: Addition of hydrochloric acid A Golden yellow White precipitate is No observable change flame formed B Brick-red flame No observable change A gas is evolved which can turn limewater milky According to test 1, what metals are present in A and B respectively? A: Sodium [1] B: Calcium [1] (b) According to tests 2 and 3, explain briefly what are present in A and B respectively. A: Chloride (ions) [1] A forms white precipitate (silver chloride) in silver nitrate test. [1] B: Carbonate (ions) [1] B reacts with hydrochloric acid to produce carbon dioxide which turns limewater milky. [1] (c) Name substances A and B. A: Sodium chloride [1] B: Calcium carbonate [1] (d) State ONE source of substances A and B respectively. A: Sea water [1] B: Limestone/ marble/ chalk [1] (e) What will happen if (i) A is heated strongly? No reaction [1] (ii) B is heated strongly? Calcium carbonate decomposes on heating to give calcium oxide and carbon dioxide. [1] (12 marks)

10 8. Consider three substances: chalk, limestone and marble. (a) (i) What is the common substance present in chalk, limestone and marble? Calcium carbonate [1] (ii) Suggest chemical tests for the presence of this substance in limestone. Calcium ions: Give brick-red flame in flame test [1, 1] Carbonate ions: Add dilute hydrochloric acid to limestone, [1] a gas is evolved which turns limewater milky. [1] (b) Which substance is the hardest? Marble is the hardest. [1] (c) State the conditions for the conversion of limestone to marble. Limestone changes to marble under high pressure and high temperature. [2] (d) Suggest ONE use of limestone. Making cement/ glass/ materials for construction [1] (e) A chalk is heated strongly. (i) What will happen if chalk is heated strongly? Chalk (calcium carbonate) will decompose to give calcium oxide and carbon dioxide. [1] (ii) Water is added to the solid remained after heating. Solution Y is formed. (1) Write a word equation for the reaction. Calcium oxide + water calcium hydroxide [1] (2) State ONE use of solution Y. As limewater [1] (f) What will be observed when a piece of chalk is added into dilute hydrochloric acid? Write a word equation for the reaction. Chalk dissolves. [1] Gas bubbles evolve (effervescence). [1] Calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide [1] (15 marks)

11 9. The following diagram shows some natural processes in our environment. (a) What is Process 1? Evaporation of sea water (water) [1] (b) Classify the above processes into physical change(s) and chemical change(s). Process 1: Physical change [1] Process 2: Physical change [1] Process 3: Physical change and chemical change [1] (c) Explain briefly how rainwater causes the erosion of limestone. Carbon dioxide in air dissolves in water to form carbonic acid. [1] Carbonic acid reacts with calcium carbonate to form soluble calcium hydrogencarbonate which is washed away readily. [1] (d) (i) What is the main constitute substance left after a sample of sea water is evaporated to dryness? Table salt/ sodium chloride [1] (ii) Suggest TWO uses of this substance in our daily lives. As preservative and flavouring agent [1, 1] (e) Pure water can be obtained from distillation of sea water. (i) Does distillation of sea water involve a physical or chemical change? It involves a physical change. [1] (ii) Draw a labelled diagram of experimental set-up for simple distillation of sea water. (1 mark for correct set-up; 1 mark for labelling anti-bumping granules and thermometer; 1 mark for labelling sea water and water) [3] (13 marks)

12 10. A student carried out an experiment on thermal decomposition of limestone. (a) (i) What is the major component of limestone? Calcium carbonate/ CaCO 3 [1] (ii) Give the name of a natural occurring substance which has the same major component as limestone. Chalk/ marble [1] (b) Write a word equation for thermal decomposition of limestone. (c) Calcium carbonate calcium oxide + carbon dioxide [1] A gas is evolved in thermal decomposition of limestone. (i) Draw an experimental set-up to identify the gas. (ii) [2] State any observable change for the test. Write a word equation for the change. (d) Limewater turns milky. [1] Calcium hydroxide + carbon dioxide calcium carbonate + water [1] Describe briefly how you can test the presence of calcium ion in limestone. Dip a clean nichrome wire into concentrated hydrochloric acid. [1] Dip the nichrome wire into powdered limestone. [1] Heat the wire in Bunsen flame. [1] Abrick-red flame is observed. [1] (11 marks)

13 11. Answer the questions with reference to the diagram below. (a) Name substances A, B and C. A: Calcium carbonate [1] B: Calcium oxide [1] C: Limewater /calcium hydroxide solution [1] (b) What should process X be? Addition of water [1] (c) Write a word equation for (i) the decomposition of substance A on strong heating; and (d) (e) Calcium carbonate calcium oxide + carbon dioxide [1] (ii) addition of dilute hydrochloric acid to substance A. Calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide [1] When carbon dioxide is bubbled into substance C, what will be observed? Write the word equation for the reaction involved. Limewater (Solution C) turns milky. [1] Calcium hydroxide + carbon dioxide calcium carbonate + water [1] A student wants to obtain pure calcium chloride crystals from calcium chloride solution. (i) Describe briefly how he can obtain the crystals from the solution. 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 small amount of cold water. Dry them with filter paper. [1] (ii) The student cannot distinguish between sodium chloride crystals and calcium chloride crystals. Suggest a chemical test that allows him to distinguish them. Flame test [1] Sodium chloride gives golden yellow flame [1] Calcium chloride gives brick-red flame. [1] (14 marks)

14 12. Describe briefly, using the following apparatus and materials, how you can distinguish hydrated 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 give a paragraph-length answer. In this question, 6 marks will be awarded for chemical knowledge and 3 marks for effective communication.) Heat these three substances in test tubes separately. [1] Place a dry cobalt(ii) chloride paper near the mouth of each test tube. [1] Only hydrated calcium chloride turns the paper from blue to pink as water of crystallization is evaporated. [1] Detect any gas evolved with limewater. [1] Only calcium carbonate turns limewater milky as calcium carbonate decomposes on heating to give carbon dioxide. [1] Calcium oxide is stable on strong heating. [1] (3 marks for effective communication) (9 marks) 13. Suppose 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 give a paragraph-length answer. In this question, 6 marks will be awarded for chemical knowledge and 3 marks for effective communication.) Dissolve 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. Large sodium chloride crystals are obtained. [1] Filter off the crystals. [1] Wash the crystals with small amount of cold water and dry them with filter paper. [1] (3 marks for effective communication) (9 marks)