9701_w07_qp_2
A paper of Chemistry, 9701
Questions:
5
Year:
2007
Paper:
2
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0
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1
This question is about the bonding of covalent compounds. On the axes below, sketch the shapes of a 1s, a 2s, and a 2px orbital. z x y 1s z x y 2s z x y 2px Covalent bonding occurs when two atoms share a pair of electrons. Covalent bonding may also be described in terms of orbital overlap with the formation of σ bonds. How are the two atoms in a covalent bond held together? In your answer, state which particles are attracted to one another and the nature of the force of attraction. Draw sketches to show orbital overlap that produces the σ bonding in the H2 and HCl molecules. H2 HCl The bond in the HCl molecule is said to be ‘polar’. What is meant by the term bond polarity? Explain why the HCl molecule is polar. Examiner’s Use The bonding in ethene may be described as a mixture of σ and π bonding. Each carbon atom in ethene forms three σ bonds as shown below. C H H H H C On the diagram, sketch the π bond that is also present in ethene. Carbon, hydrogen and ethene each burn exothermically in an excess of air. C+ O2→ CO2∆H o c = –393.7 kJ mol–1 H2+ ½O2→ H2O∆H o c = –285.9 kJ mol–1 C2H4+ 3O2→ 2CO2+ 2H2O∆H o c = –1411.0 kJ mol–1 Use the data to calculate the standard enthalpy change of formation, ∆H o f , in kJ mol–1, of ethene at 298 K. 2C+ 2H2→ C2H4∆H o f = kJ mol–1
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
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Use This question concerns the chlorides of the elements sodium to phosphorus of the third period of the Periodic Table. The melting points of these chlorides are given below. compound sodium chloride magnesium chloride aluminium chloride silicon tetrachloride phosphorus(chloride melting point/K 451* *sublimes at 451 K Give the equation, with state symbols, for the reaction of phosphorus with chlorine to form phosphorus(chloride, PCl5. Suggest, in terms of the structure and bonding, explanations for the following. You should draw diagrams where you think they will help your answer. the high melting point of sodium chloride the low melting point of silicon tetrachloride Examiner’s Use Write an equation for the reaction of silicon tetrachloride with water. What is the pH of the solution formed when each of the following compounds is dissolved in water? NaCl PCl5 When solid aluminium chloride is heated above 451 K, a vapour is formed which has Mr = 267. When this vapour is heated above 1100 K, the vapour has Mr = 133.5. What are the molecular formulae of these two forms of aluminium chloride? at 460 K at 1150 K Draw a ‘dot-and-cross’ diagram of the form of aluminium chloride that exists at the higher temperature. Draw a displayed formula of the form of aluminium chloride that exists at the lower temperature. Indicate clearly the different types of bonds present.
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
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Use The elements phosphorus, sulphur, and chlorine are regarded as having simple molecular structures. What are the molecular formulae of each of these three elements? phosphorus sulphur chlorine Place the three elements in order of their melting points with the highest first. highest lowest Suggest an explanation for the order you have given in . Examiner’s Use Sulphur and chlorine can be reacted together to form disulphur dichloride, S2Cl2. Disulphur dichloride, S2Cl2, is decomposed by water forming sulphur and a mixture of hydrochloric acid and sulphurous acid. When 2.7 g of S2Cl2 is reacted with an excess of water, 0.96 g of sulphur, S, is produced. What is the amount, in moles, of S2Cl2 present in 2.7 g? What is the amount, in moles, of S produced from 1.0 mol of S2Cl2? Construct a balanced equation for the reaction of S2Cl2 with water. The reaction between S2Cl2 and water is a redox reaction. Which product has been formed by oxidation and which by reduction? product formed by oxidation product formed by reduction
11. Group 17  →  11.4. The reactions of chlorine
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
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Use The molecular formula of a compound states the number of atoms of each element that are present in one molecule. It contains no information about the structure of the molecule. Hydrocarbons with the molecular formula C5H10 may be branched chain, straight chain or cyclic. Draw a displayed formula of C5H10 as a branched chain hydrocarbon. Pent-2-ene is one straight chain hydrocarbon with formula C5H10. Pent-2-ene exhibits cis-trans isomerism. Draw and label the structural formulae of the two cis-trans isomers of pent-2-ene. In the spaces below draw the structural formulae of two alcohols which would each produce pent-2-ene on dehydration. Examiner’s Use One of these alcohols exhibits optical isomerism. Draw the structural formulae of the two isomers of this alcohol. Your structures should clearly indicate the three-dimensional nature of the structures. Pent-2-ene decolourises aqueous bromine. Suggest the structural formula of an isomer of C5H10 which does not decolourise aqueous bromine. Pent-2-ene can be polymerised. Draw a section of the polymer chain produced showing two repeat units.
13. An introduction to AS Level organic chemistry  →  13.4. Isomerism: structural isomerism and stereoisomerism
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
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Use Ethanoic acid, CH3CO2H, is formed as vinegar by the bacterial oxidation of ethanol present in wine and other solutions. CH3CH2OH + 2[O] → CH3CO2H + H2O Ethanoic acid can also be formed in the laboratory by the oxidation of ethanol. What oxidising agent is used for this laboratory reaction? What colour change would be observed? from to When ethanoic acid is prepared in this way in the laboratory, the reagents are heated under reflux for some time before the ethanoic acid is separated. Why is the reaction carried out by heating under reflux? What would be the main organic compound formed if, instead of heating under reflux, the reagents were heated together and the products immediately distilled off? Ethanoic acid is manufactured from methanol, CH3OH, by reacting it with carbon monoxide in the presence of a catalyst containing rhodium metal and iodide ions. CH3OH + CO → CH 3CO2H The reaction proceeds in a number of stages. One stage in this process is the reaction of methanol with hydrogen iodide. What organic compound is formed in this reaction? A later stage involves the conversion of an intermediate compound. CH3C=O → CH3C=O I OH What type of reaction is this? Examiner’s Use Methanol can be converted into ethanoic acid in the laboratory in a three-stage process. CH3OH step I CH3I step II CH3CN step III CH3CO2H What reagentand conditions are used in each step of the conversion? step I reagentconditions step II reagentconditions step III reagentconditions
18. Carboxylic acids and derivatives  →  18.1. Carboxylic acids
16. Hydroxy compounds  →  16.1. Alcohols
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
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