9701_s06_qp_2
A paper of Chemistry, 9701
Questions:
5
Year:
2006
Paper:
2
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0
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Examiner s Use Mohr’s salt is a pale green crystalline solid which is soluble in water. Mohr’s salt is a ‘double salt’ which contains two cations, one of which is Fe2+, one anion which is SO4 2–, and water of crystallisation. The identity of the second cation was determined by the following test. Solid Mohr’s salt was heated with solid sodium hydroxide and a colourless gas was evolved. The gas readily dissolved in water giving an alkaline solution. What is the gas? What is the formula of the second cation identified by this test? In this test, a grey/green solid residue was also formed. Suggest a name or formula for this solid. The identity of the anion present in Mohr’s salt was confirmed by adding dilute hydrochloric acid followed by aqueous barium chloride to an aqueous solution of Mohr’s salt. A white precipitate was formed. Suggest the identity of the white precipitate. When a double salt such as Mohr’s salt is made, the two individual salts are mixed together in a 1:1 molar ratio, dissolved in water and the solution crystallised. Give the formula of each of the two salts that would be mixed to make the double salt, Mohr’s salt. salt 1 salt 2 For Examiner’s Use Calculate the relative formula mass of each of the salts present in Mohr’s salt. salt 1 relative formula mass of salt 1 salt 2 relative formula mass of salt 2 The crystals of the double salt contain water of crystallisation. The relative formula mass of Mohr’s salt is 392. Use your answers to to calculate the number of moles of water of crystallisation present in one mole of Mohr’s salt.
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
4. States of matter  →  4.2. Bonding and structure
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
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For Examiner’s Use The unsaturated hydrocarbon ethyne , C2H2, is widely used in ‘oxy-acetylene torches’ for cutting and welding metals. In the torch, ethyne is burned in oxygen to produce a flame with a temperature of 3400 K. Ethyne is a linear molecule with a triple bond, CC, between the two carbon atoms. Draw a ‘dot-and-cross’ diagram of an ethyne molecule. When used for cutting or welding, ethyne is transported in cylinders which contain the gas under pressure. A typical cylinder has a volume of 76 dm3 and contains ethyne gas at 1515 kPa pressure at a temperature of 25 °C. Use the general gas equation, pV = nRT, to calculate the amount, in moles, of ethyne in this cylinder. In some countries, ethyne is manufactured from calcium carbide, CaC2, which is produced by heating quicklime and coke together at 2300 K. CaO + 3C CaC2 + CO When water is added to the CaC2, calcium hydroxide, Ca(OH)2, and ethyne, C2H2, are produced. Construct a balanced equation for the formation of ethyne from calcium carbide. Use this equation and your answer to part to calculate the mass of CaC2 which will react with an excess of water to produce enough ethyne to fill 100 cylinders of the gas. For Examiner’s Use The equation for the complete combustion of ethyne is given below. Use appropriate bond energy data from the Data Booklet to calculate a value for the enthalpy change of combustion of ethyne. C2H2+ ⁵⁄₂O22CO2+ H2O The value for the standard enthalpy change of combustion of ethyne is –1300 kJ mol–1. Define the term standard enthalpy change of combustion. Explain why your answer to does not have the same value as the standard enthalpy change of combustion.
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
2. Atoms, molecules and stoichiometry  →  2.4. Reacting masses and volumes (of solutions and gases)
14. Hydrocarbons  →  14.1. Alkanes
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For Examiner’s Use This question is about the elements of Group VII, the halogens. Complete the following table. halogen colour physical state at room temperature chlorine bromine iodine Concentrated sulphuric acid is added to separate solid samples of magnesium chloride, magnesium bromide, and magnesium iodide. Describe, in each case, one observation you would be able to make. MgCl2 MgBr2 MgI2 Give an equation for the reaction of concentrated sulphuric acid with magnesium chloride. When dilute nitric acid and aqueous silver nitrate are added to a solution of a magnesium halide, MgX2, a pale cream precipitate is formed. This precipitate is soluble in concentrated aqueous ammonia but not soluble in dilute aqueous ammonia. What is the identity of the precipitate? Give an equation, with state symbols, for the reaction of the precipitate with concentrated aqueous ammonia. For Examiner’s Use A hot glass rod is plunged into separate gas jars, one containing hydrogen chloride and one containing hydrogen iodide. For each gas, state what you would observe, if anything, and write an equation for any reaction that takes place. HCl HI Explain your answer to in terms of enthalpy changes. What is the role of the hot glass rod in any reaction that occurs?
11. Group 17  →  11.2. The chemical properties of the halogen elements and the hydrogen halides
11. Group 17  →  11.3. Some reactions of the halide ions
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For Examiner’s Use Compounds containing the allyl group, CH2=CHCH2− , have pungent smells and are found in onions and garlic. Allyl alcohol, CH2=CHCH2OH, is a colourless liquid which is soluble in water. Allyl alcohol behaves as an alkene and as a primary alcohol. Give the structural formula of the organic compound formed when allyl alcohol is reacted with Br2, heated under reflux with an acidified solution of Cr2O7 2– ions. When allyl alcohol is reacted with MnO2 at room temperature, propenal, CH2=CHCHO is formed. What type of reaction is this? Allyl alcohol may be converted into propanal, CH3CH2CHO, by using a ruthenium(catalyst in water. CH2=CHCH2OH ruthenium(catalyst CH3CH2CHO The reactant and the product are isomers. What form of isomerism do they display? For Examiner’s Use Allyl alcohol can be converted into propanal in two steps without the use of a ruthenium(catalyst. CH2=CHCH2OH step I CH3CH2CH2OH step II CH3CH2CHO What reagents and conditions would be used for each step? step I reagentconditionstep II reagentconditionBy considering your answers to and , suggest what is unusual about the single- step reaction in . Suggest the structural formula of the organic compound formed when allyl alcohol is reacted with cold, dilute MnO4 – ions, heated under reflux with acidified MnO4 – ions.
16. Hydroxy compounds  →  16.1. Alcohols
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
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For Examiner’s Use Many organic reactions are substitution reactions in which the number of carbon atoms in the organic compound is unchanged. What is meant by the term substitution reaction? One example of a substitution reaction is the formation of an alcohol from a halogenoalkane. Write a balanced equation for the formation of ethanol from bromoethane. State the conditions for this reaction. In a few organic reactions, the product contains one more carbon atom than the starting material. Write the equation for a reaction in which the organic compound bromoethane, which contains two carbon atoms, is converted into an organic compound which contains three carbon atoms. State the conditions for this reaction. Ethanol may be converted into propanoic acid in a three-stage process which uses ethanol as the only organic compound. C2H5OH step I K step II L step III C2H5CO2H Give the structural formulae of the intermediate compounds K and L. K L State the reagentused and give the essential conditionfor step I and for step III. step I reagentconditionstep III reagentcondition
13. An introduction to AS Level organic chemistry  →  13.2. Characteristic organic reactions
21. Organic synthesis  →  21.1. Organic synthesis
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