0620_w12_qp_33
A paper of Chemistry, 0620
Questions:
7
Year:
2012
Paper:
3
Variant:
3
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1
For Examiner’s Use For each of the following, select an element from Period 4, potassium to krypton, which matches the description. A metal that reacts rapidly with cold water to form a compound of the type M(OH)2 and hydrogen. Its only oxidation state is 0. It has a macromolecular oxide, XO2, which has similar physical properties to those of diamond. This is one of the metals alloyed with iron in stainless steel. It can be reduced to an ion of the type X–. It can form a covalent hydride having the formula H2X. Its soluble salts are blue and its oxide is black. It is a liquid at room temperature.
9. Metals  →  9.4. Reactivity series
9. Metals  →  9.1. Properties of metals
8. The Periodic Table  →  8.2. Group I properties
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3
For Examiner’s Use A small amount of liquid bromine is added to a container which is then sealed. Br2→ Br2Use the ideas of the Kinetic Theory to explain why, after about an hour, the bromine molecules have spread uniformly to occupy the whole container. The diagrams below show simple experiments on the speed of diffusion of gases. diagram 1 diagram 2 porous pot allows gas molecules to diffuse air porous pot air air hydrogen large beaker large beaker carbon dioxide same level coloured liquid higher level diagram 3 higher level air
1. States of matter  →  1.2. Diffusion
1. States of matter  →  1.1. Solids, liquids and gases
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4
For Examiner’s Use Zinc alloys have been used for over 2500 years. Explain the phrase zinc alloy. Making alloys is still a major use of zinc. State one other large scale use of zinc. Describe the bonding in a typical metal, such as zinc, and then explain why it is malleable. You may use a diagram to illustrate your answer. Suggest why the introduction of a different atom into the structure makes the alloy less malleable than the pure metal. Zinc metal is made by the reduction of zinc oxide. The major ore of zinc is zinc blende, ZnS. Zinc blende contains silver and lead compounds as well as zinc sulfi de. Zinc blende is converted into impure zinc oxide by heating it in air. 2ZnS + 3O2 → 2ZnO + 2SO2 Describe how zinc oxide is reduced to zinc. Some of the zinc oxide is dissolved in sulfuric acid to make aqueous zinc sulfate. Write a balanced symbol equation for this reaction. For Examiner’s Use This impure solution of zinc sulfate contains zinc ions, silver(ions and lead ions. Explain why the addition of zinc powder produces pure zinc sulfate solution. Include at least one ionic equation in your explanation. Describe how zinc metal can be obtained from zinc sulfate solution by electrolysis. A labelled diagram is acceptable. Include all the products of this electrolysis. The electrolysis is similar to that of copper(sulfate solution with inert electrodes.
9. Metals  →  9.5. Corrosion of metals
9. Metals  →  9.4. Reactivity series
9. Metals  →  9.3. Alloys and their properties
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5
For Examiner’s Use Propenoic acid is an unsaturated carboxylic acid. The structural formula of propenoic acid is given below. C C H H COOH H Describe how you could show that propenoic acid is an unsaturated compound. test result Without using an indicator, describe how you could show that a compound is an acid. test result Propenoic acid reacts with ethanol to form an ester. Deduce the name of this ester. Draw its structural formula. name of ester structural formula showing all bonds An organic compound has a molecular formula C6H8O4. It is an unsaturated carboxylic acid. One mole of the compound reacts with two moles of sodium hydroxide. Explain the phrase molecular formula. For Examiner’s Use One mole of this carboxylic acid reacts with two moles of sodium hydroxide. How many moles of –COOH groups are there in one mole of this compound? What is the formula of another functional group in this compound? Deduce a structural formula of this compound.
11. Organic chemistry  →  11.7. Carboxylic acids
11. Organic chemistry  →  11.1. Formulae, functional groups and terminology
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For Examiner’s Use Until recently, arsenic poisoning, either deliberate or accidental, has been a frequent cause of death. The symptoms of arsenic poisoning are identical with those of a common illness, cholera. A reliable test was needed to prove the presence of arsenic in a body. In 1840, Marsh devised a reliable test for arsenic. hydrochloric acid H2 and arsine burning pieces of zinc and arsenic compound black stain shows presence of arsenic cold surface Hydrogen is formed in this reaction. Any arsenic compound reacts with this hydrogen to form arsine which is arsenic hydride, AsH3. The mixture of hydrogen and arsine is burnt at the jet and arsenic forms as a black stain on the glass. Write an equation for the reaction which forms hydrogen. Draw a diagram which shows the arrangement of the outer electrons in one molecule of the covalent compound arsine. The electron distribution of arsenic is 2 + 8 + 18 + 5. Use x to represent an electron from an arsenic atom. Use o to represent an electron from a hydrogen atom. For Examiner’s Use Another hydride of arsenic has the composition below. arsenic 97.4 % hydrogen 2.6 % Calculate the empirical formula of this hydride from the above data. Show your working. The mass of one mole of this hydride is 154 g. What is its molecular formula? Deduce the structural formula of this hydride. Hair is a natural protein. Hair absorbs arsenic from the body. Analysis of the hair provides a measurement of a person’s exposure to arsenic. To release the absorbed arsenic for analysis, the protein has to be hydrolysed. What is the name of the linkage in proteins? Name a reagent which can be used to hydrolyse proteins. What type of compound is formed by the hydrolysis of proteins? For Examiner’s Use In the 19th Century, a bright green pigment, copper(arsenate(was used to kill rats and insects. In damp conditions, micro-organisms can act on this compound to produce the very poisonous gas, arsine. Suggest a reason why it is necessary to include the oxidation states in the name of the compound. The formula for the arsenate(ion is AsO4 3–. Complete the ionic equation for the formation of copper(arsenate(. Cu2+ + AsO4 3– →
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
11. Organic chemistry  →  11.5. Alkenes
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For Examiner’s Use Ammonia is made by the Haber process. N2+ 3H22NH3State one major use of ammonia. Describe how hydrogen is obtained for the Haber process. This reaction is carried out at a high pressure, 200 atmospheres. State, with an explanation for each, two advantages of using a high pressure. What is the difference between an endothermic and an exothermic reaction? For Examiner’s Use Bond breaking is an endothermic process. Bond energy is the amount of energy needed to break or form one mole of the bond. Complete the table and explain why the forward reaction is exothermic. N N + 3 H H 2 H N H H bond bond energy kJ / mol energy change kJ exothermic or endothermic N N +944 endothermic H — H 3 × 436 = +1308 N — H
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
5. Chemical energetics  →  5.1. Exothermic and endothermic reactions
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