0620_w13_qp_32
A paper of Chemistry, 0620
Questions:
7
Year:
2013
Paper:
3
Variant:
2
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1
For Examiner’s Use The table gives the melting points, the boiling points and the electrical properties of six substances A to F. substance melting point / °C boiling point / °C electrical conductivity as a solid electrical conductivity as a liquid A –210 –196 does not conduct does not conduct B does not conduct good conductor C good conductor good conductor D –94 does not conduct does not conduct E does not conduct does not conduct F good conductor good conductor Which two substances could be metals? Which substance could be nitrogen? Which substance is an ionic solid? Which substance is a liquid at room temperature? Which substance has a giant covalent structure similar to that of diamond? Which two substances could exist as simple covalent molecules?
2. Atoms, elements and compounds  →  2.4. Ions and ionic bonds
2. Atoms, elements and compounds  →  2.5. Simple molecules and covalent bonds
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For Examiner’s Use The halogens are a collection of diatomic non-metals in Group VII. Defi ne the term diatomic. What do the electron distributions of the halogens have in common? How do their electron distributions differ? Complete the table. halogen solid, liquid or gas at room temperature colour chlorine bromine iodine The halogens react with other non-metals to form covalent compounds. Draw a diagram which shows the arrangement of the valency electrons in one molecule of the covalent compound arsenic trifl uoride. The electron distribution of an arsenic atom is 2 + 8 + 18 + 5. Use x to represent an electron from an arsenic atom. Use o to represent an electron from a fl uorine atom. For Examiner’s Use Photochromic glass is used in sunglasses. In bright light, the glass darkens reducing the amount of light reaching the eye. When the light is less bright, the glass becomes colourless increasing the amount of light reaching the eye. Photochromic glass contains very small amounts of the halides silver(chloride and copper(chloride. The reaction between these two chlorides is photochemical. AgCl + CuCl Ag + CuCl 2 colourless colourless black colourless How does photochromic glass work?
8. The Periodic Table  →  8.3. Group VII properties
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For Examiner’s Use Nitric acid is now made by the oxidation of ammonia. It used to be made from air and water. This process used very large amounts of electricity. Air was blown through an electric arc and heated to 3000 °C. N2+ O22NOequilibrium 1 nitric oxide The equilibrium mixture leaving the arc contained 5 % of nitric oxide. This mixture was cooled rapidly. At lower temperatures, nitric oxide will react with oxygen to form nitrogen dioxide. 2NO+ O22NO2 equilibrium 2 Nitrogen dioxide reacts with oxygen and water to form nitric acid. Suggest a reason why the yield of nitric oxide in equilibrium 1 increases with temperature. What effect, if any, would increasing the pressure have on the percentage of nitric oxide in equilibrium 1? Explain your answer. Deduce why equilibrium 2 is only carried out at lower temperatures. Complete the equation for the reaction between nitrogen dioxide, water and oxygen to form nitric acid. NO2 + O2 + → HNO3 Ammonia is more expensive than water and air. Suggest a reason why the ammonia-based process is preferred to the electric arc process. For Examiner’s Use Nitric acid is used to make the fertiliser ammonium nitrate, NH4NO3. What advantage has this fertiliser over another common fertiliser, ammonium sulfate, (NH4)2SO4? Plants need nitrogen to make chlorophyll. Explain why chlorophyll is essential for plant growth.
10. Chemistry of the environment  →  10.3. Air quality and climate
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
10. Chemistry of the environment  →  10.2. Fertilisers
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For Examiner’s Use For centuries, iron has been extracted from its ore in the blast furnace. The world production of pig iron is measured in hundreds of million tonnes annually. The following raw materials are supplied to a modern blast furnace. iron ore which is hematite, Fe2O3 limestone which is calcium carbonate carbon in the form of coke air Describe the essential reactions in the blast furnace. Each of the four raw materials must be mentioned at least once. Give the equation for the reduction of hematite. Each year, blast furnaces discharge millions of tonnes of carbon dioxide into the atmosphere. This will increase the percentage of atmospheric carbon dioxide. Explain why this increased percentage of carbon dioxide may cause problems in the future. Until the early eighteenth century, charcoal, not coke, was used in the blast furnace. Charcoal is made from wood but coke is made from coal. Explain why the use of charcoal would have a smaller effect on the level of atmospheric carbon dioxide. For Examiner’s Use A method being developed to produce iron with lower emissions of carbon dioxide is by electrolysis. Hematite, Fe2O3, is dissolved in molten lithium carbonate and electrolysed. The ore is spilt into its constituent elements. Write an equation for the reaction at the negative electrode . Complete the equation for the reaction at the positive electrode . O2– → +
9. Metals  →  9.6. Extraction of metals
4. Electrochemistry  →  4.1. Electrolysis
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For Examiner’s Use Silver(chromate(is an insoluble salt. It is prepared by precipitation. 20 cm3 of aqueous silver(nitrate, concentration 0.2 mol / dm3, was mixed with 20 cm3 of aqueous potassium chromate(, concentration 0.1 mol / dm3. After stirring, the mixture was fi ltered. The precipitate was washed several times with distilled water. The precipitate was then left in a warm oven for several hours. 2AgNO3+ K2CrO4→ Ag2CrO4+ 2KNO3What diffi culty arises if the name of a compound of a transition element does not include its oxidation state, for example iron oxide? These questions refer to the preparation of the salt. Why is it necessary to fi lter the mixture after mixing and stirring? What is the purpose of washing the precipitate? Why leave the precipitate in a warm oven? Explain why the concentrations of silver(nitrate and potassium chromate(are different. What mass of silver(nitrate is needed to prepare 100 cm3 of silver(nitrate solution, concentration 0.2 mol / dm3? The mass of one mole of AgNO3 is 170 g. What is the maximum mass of silver(chromate(which could be obtained from 20 cm3 of aqueous silver(nitrate, concentration 0.2 mol / dm3? number of moles of AgNO3 used = number of moles of Ag2CrO4 formed = mass of one mole of Ag2CrO4 = 332 g mass of Ag2CrO4 formed = g
7. Acids, bases and salts  →  7.3. Preparation of salts
9. Metals  →  9.4. Reactivity series
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For Examiner’s Use The following reactivity series shows both familiar and unfamiliar elements in order of decreasing reactivity. Each element is represented by a redox equation. Rb Rb+ + e– Mg Mg2+ + 2e– Mn Mn2+ + 2e– Zn Zn2+ + 2e– H2 2H+ + 2e– Cu Cu2+ + 2e– Hg Hg2+ + 2e– Two of the uses of the series are to predict the thermal stability of compounds of the metals and to explain their redox reactions. Most metal hydroxides decompose when heated. Complete the equation for the thermal decomposition of copper(hydroxide. Cu(OH)2 → + Choose a metal from the above series whose hydroxide does not decompose when heated. Defi ne in terms of electron transfer the term oxidation. Explain why the positive ions in the above equations are oxidising agents. Which metals in the series above do not react with dilute acids to form hydrogen? Describe an experiment which would confi rm the prediction made in . Which metal in the series above can form a negative ion which gives a pink / purple solution in water? Describe what you would observe when zinc, a reducing agent, is added to this pink / purple solution.
9. Metals  →  9.4. Reactivity series
6. Chemical reactions  →  6.4. Redox
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For Examiner’s Use Plants can make complex molecules from simple starting materials, such as water, carbon dioxide and nitrates. Substances produced by plants include sugars, more complex carbohydrates, esters, proteins, vegetable oils and fats. Describe how you could decide from its molecular formula whether a compound is a carbohydrate. Plants can change the sugar, glucose, into starch which is a more complex carbohydrate. What type of reaction is this? The fermentation of glucose can be carried out in the apparatus shown below. After a few days the reaction stops. A 12% aqueous solution of ethanol has been produced. water allows carbon dioxide to escape but prevents air from entering aqueous glucose and yeast The enzyme, zymase, catalyses the anaerobic respiration of the yeast. Explain the term respiration. Complete the equation. C6H12O6 → + glucose ethanol carbon dioxide Why must air be kept out of the fl ask? For Examiner’s Use The ester methyl butanoate is found in apples. It can be made from butanoic acid and methanol. Their structural formulae are given below. C H H C O O H C H H C H H H H O C H H H butanoic acid methanol Use the information given above to deduce the structural formula of methyl butanoate showing all the bonds. The equation represents the hydrolysis of a naturally occurring ester. C17H35 CO2 CH2 C17H35 CO2 3C17H35COONa CHOH CH 3NaOH + + → C17H35 CO2 CH2 CH2OH CH2OH Which substance in the equation is an alcohol? Put a ring around this substance in the equation above. Is the alkyl group, C17H35, in this ester saturated or unsaturated? Give a reason for your choice. What type of compound is represented by the formula C17H35COONa? What is the major use for compounds of this type? type of compound use For Examiner’s Use Proteins are natural macromolecules. Draw the structural formula of a typical protein. Include three monomer units. You may represent amino acids by formulae of the type drawn below. H2N COOH H2N COOH
11. Organic chemistry  →  11.6. Alcohols
11. Organic chemistry  →  11.2. Naming organic compounds
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