0620_w06_qp_3
A paper of Chemistry, 0620
Questions:
8
Year:
2006
Paper:
3
Variant:
0
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1
For Examiner's Use Choose a gas from the following list to answer the questions below. Each gas may be used once, more than once or not at all. ammonia argon carbon dioxide carbon monoxide chlorine ethene hydrogen nitrogen oxygen Which gas is a noble gas, is an acidic oxide, can be polymerised, is the active component of air, is used in the treatment of water, is a product of respiration?
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
11. Organic chemistry  →  11.3. Fuels
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2
For Examiner's Use The table shows the melting points, boiling points and electrical properties of the six substances A to F. substance melting point / oC boiling point / oC electrical conductor at room temperature electrical conductor of substance dissolved in water A good does not dissolve B does not conduct does not dissolve C very poor very poor D does not conduct good E –5 to -10 102 to 105 good good F -85 -60 does not conduct does not dissolve Which three substances are solids at room temperature? Which one is an ionic compound? Which one is a gas at room temperature? Which two substances are liquids at room temperature? Which substance is a metal? Which one is an impure substance?
2. Atoms, elements and compounds  →  2.5. Simple molecules and covalent bonds
2. Atoms, elements and compounds  →  2.4. Ions and ionic bonds
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3
For Examiner's Use Calcium carbonate is an important raw material. Name a rock which is made up of calcium carbonate. When calcium carbonate is heated strongly, it decomposes. CaCO3 → CaO + CO2 Calculate the relative formula mass of: CaCO3 CaO 7.00 kg of calcium oxide was formed. What mass of calcium carbonate was heated? Calcium carbonate is used to control soil acidity. Why is it important to control soil acidity? Both calcium carbonate, insoluble in water, and calcium oxide, slightly soluble, are used to increase soil pH. Suggest two advantages of using calcium carbonate. Give one use of calcium carbonate other than for making calcium oxide and controlling soil pH.
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
9. Metals  →  9.6. Extraction of metals
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4
For Examiner's Use Minimising air pollution is essential for health and for the environment. Natural gas is methane. Write the equation for complete combustion of methane. Explain why it is dangerous to use a gas fire in a poorly ventilated room. Low sulphur fuels are being introduced. Ordinary diesel contains 500 ppm of sulphur but low sulphur diesel contains less than 50 ppm. Why is this an advantage to the environment? Catalytic converters reduce pollution from motor vehicles, as shown in the following diagram. oxides of nitrogen carbon monoxide unburnt hydrocarbons less harmful gases to atmosphere catalysts rhodium, platinum, palladium What type of elements are the metals rhodium, platinum and palladium? Rhodium catalyses the decomposition of the oxides of nitrogen. 2NO → N2 + O2 Two other pollutants are carbon monoxide and unburnt hydrocarbons. How are they made into less harmful substances?
10. Chemistry of the environment  →  10.3. Air quality and climate
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5
For Examiner's Use Ammonia is manufactured by the Haber Process. N2+ 3H22NH3200 atmospheres 450°C The forward reaction is exothermic. What is the catalyst for this reaction? Newer catalysts have been discovered for this process. Using these catalysts, the operating temperature is lowered from 450°C to 400°C. What is the advantage of using a lower temperature? Explain your answer. advantage explanation After passing over the catalyst, the mixture contains 15% of ammonia. It is cooled and the ammonia liquefies and is separated from the unreacted nitrogen and hydrogen. They are recycled. How are the gases recycled? Only ammonia gas liquefies. Suggest an explanation for this. Urea, CO(NH2)2, is one of the fertilisers manufactured from ammonia. Ammonia is heated with carbon dioxide. Write an equation for the manufacture of urea. Explain why urea on its own might not be very effective in promoting crop growth. For Examiner's Use Give a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound urea. Its structural formula is given below. O C N H H N H H Use ο to represent an electron from a carbon atom. Use x to represent an electron from a hydrogen atom. Use • to represent an electron from a nitrogen atom.
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
11. Organic chemistry  →  11.5. Alkenes
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6
For Examiner's Use An ore of copper is the mineral, chalcopyrite. This is a mixed sulphide of iron and copper. Analysis of a sample of this ore shows that 13.80 g of the ore contained 4.80 g of copper, 4.20 g of iron and the rest sulphur. Complete the table and calculate the empirical formula of chalcopyrite. copper iron sulphur composition by mass / g 4.80 4.20 number of moles of atoms simplest mole ratio of atoms The empirical formula is Impure copper is extracted from the ore. This copper is refined by electrolysis. Name; the material used for the positive electrode , the material used for the negative electrode , a suitable electrolyte. Write an ionic equation for the reaction at the negative electrode. One use of this pure copper is electrical conductors, another is to make alloys. Name the metal that is alloyed with copper to make brass. For Examiner's Use Two of the elements in chalcopyrite are the metal, copper, and the non-metal, sulphur. These have different properties. Copper is an excellent conductor of electricity and is malleable. Sulphur is a poor conductor and is not malleable, it is brittle. Explain, in terms of their structures, why this is so. difference in electrical conductivity difference in malleability
4. Electrochemistry  →  4.1. Electrolysis
9. Metals  →  9.6. Extraction of metals
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7
For Examiner's Use The rate of a reaction depends on concentration of reactants, temperature and possibly a catalyst or light. A piece of magnesium ribbon was added to 100 cm3 of 1.0 mol/dm3 hydrochloric acid. The hydrogen evolved was collected in a gas syringe and its volume measured every 30 seconds. hydrochloric acid magnesium ribbon In all the experiments mentioned in this question, the acid was in excess. The results were plotted to give a graph. time volume of hydrogen For Examiner's Use The experiment was repeated. Two pieces of magnesium ribbon were added to 100 cm3 of 1.0 mol/dm3 hydrochloric acid. Sketch this graph on the same grid and label it X. The experiment was repeated using one piece of magnesium ribbon and 100 cm3 of 1.0 mol/dm3 ethanoic acid. Describe how the shape of this graph would differ from the one given on the grid. Reaction rate increases when concentration or temperature is increased. Using the idea of reacting particles, explain why; increasing concentration increases reaction rate, increasing temperature increases reaction rate. The rate of a photochemical reaction is affected by light. A reaction, in plants, between carbon dioxide and water is photochemical. Name the two products of this reaction. This reaction will only occur in the presence of light and another chemical. Name this chemical.
6. Chemical reactions  →  6.2. Rate of reaction
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8
For Examiner's Use The three types of food are carbohydrates, proteins and fats. Aqueous starch is hydrolysed to maltose by the enzyme amylase. The formula of maltose is: HO OH O Starch is hydrolysed by dilute sulphuric acid to glucose. HO OH What is an enzyme? Draw the structure of starch. Name the technique that would show that the products of these two hydrolyses are different. Proteins have the same linkage as nylon but there is more than one monomer in the macromolecule. Draw the structure of a protein. What class of compound is formed by the hydrolysis of proteins? For Examiner's Use Fats are esters. Some fats are saturated, others are unsaturated. Write the word equation for the preparation of the ester, propyl ethanoate. Deduce the structural formula of this ester showing each individual bond. How could you distinguish between these two fats? Fat 1 has the formula CH2 – CO2 – C17H33 CH – CO2 – C17H33 CH2 – CO2 – C17H33 Fat 2 has the formula CH2 – CO2 – C17H35 CH – CO2 – C17H35 CH2 – CO2 – C17H35 test result with fat 1 result with fat 2 Both of these fats are hydrolysed by boiling with aqueous sodium hydroxide. What type of compounds are formed? and
11. Organic chemistry  →  11.5. Alkenes
11. Organic chemistry  →  11.8. Polymers
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