9701_w11_qp_21
A paper of Chemistry, 9701
Questions:
5
Year:
2011
Paper:
2
Variant:
1
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Compound A is an organic compound which contains carbon, hydrogen and oxygen. When 0.240 g of the vapour of A is slowly passed over a large quantity of heated copper(oxide, CuO, the organic compound A is completely oxidised to carbon dioxide and water. Copper is the only other product of the reaction. The products are collected and it is found that 0.352 g of CO2 and 0.144 g of H2O are formed. In this section, give your answers to three decimal places. Calculate the mass of carbon present in 0.352 g of CO2. Use this value to calculate the amount, in moles, of carbon atoms present in 0.240 g of A. Calculate the mass of hydrogen present in 0.144 g of H2O. Use this value to calculate the amount, in moles, of hydrogen atoms present in 0.240 g of A. Use your answers to calculate the mass of oxygen present in 0.240 g of A. Use this value to calculate the amount, in moles, of oxygen atoms present in 0.240 g of A. For Examiner’s Use Use your answers to to calculate the empirical formula of A. When a 0.148 g sample of A was vapourised at 60oC, the vapour occupied a volume of 67.7 cm3 at a pressure of 101 kPa. Use the general gas equation pV = nRT to calculate Mr of A. Mr = Hence calculate the molecular formula of A. Compound A is a liquid which does not react with 2,4-dinitrophenylhydrazine reagent or with aqueous bromine. Suggest two structural formulae for A. Compound A contains only carbon, hydrogen and oxygen. Explain how the information on the opposite page about the reaction of A with CuO confirms this statement.
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
2. Atoms, molecules and stoichiometry  →  2.4. Reacting masses and volumes (of solutions and gases)
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For Examiner’s Use The Periodic Table we currently use is derived directly from that proposed in 1869 by Mendeleev who had noticed patterns in the physical and chemical properties of the elements he had studied. The diagram below shows the first ionisation energies of the first 18 elements of the Periodic Table. first ionisation energy / kJ mol–1 0 1 2 3 4 5 6 7 8 9 proton number 10 11 12 13 14 15 16 17 18 H He Ne Na Ar Li Give the equation, including state symbols, for the first ionisation energy of sulfur. Explain why there is a general increase in first ionisation energies across the Period from sodium to argon. Explain why the first ionisation energy of magnesium is greater than that of aluminium. Explain why the first ionisation energy of phosphorus is greater than that of sulfur. For Examiner’s Use The table below refers to the elements of the third Period sodium to sulfur and is incomplete. element Na Mg Al Si P S conductivity high melting point high Complete the ‘conductivity’ row by using only the words ‘high’, ‘moderate’ or ‘low’. Complete the ‘melting point’ row by using only the words ‘high’ or ‘low’. When Mendeleev published his first Periodic Table, he left gaps for elements that had yet to be discovered. He also predicted some of the physical and chemical properties of these undiscovered elements. For one element, E, he correctly predicted the following properties. melting point of the element high melting point of the oxide high boiling point of the chloride low The element E was in the fourth Period and was one of the elements from gallium, proton number 31, to bromine, proton number 35. By considering the properties of the third Period elements aluminium to chlorine, suggest the identity of the fourth Period element E.
9. The Periodic Table: chemical periodicity  →  9.1. Periodicity of physical properties of the elements in Period 3
1. Atomic structure  →  1.4. Ionisation energy
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For Examiner’s Use For some chemical reactions, such as the thermal decomposition of potassium hydrogencarbonate, KHCO3, the enthalpy change of reaction cannot be measured directly. In such cases, the use of Hess’ Law enables the enthalpy change of reaction to be calculated from the enthalpy changes of other reactions. State Hess’ Law. In order to determine the enthalpy change for the thermal decomposition of potassium hydrogencarbonate, two separate experiments were carried out. experiment 1 30.0 cm3 of 2.00 mol dm–3 hydrochloric acid (an excess) was placed in a conical flask and the temperature recorded as 21.0 °C. When 0.0200 mol of potassium carbonate, K2CO3, was added to the acid and the mixture stirred with a thermometer, the maximum temperature recorded was 26.2 °C. Construct a balanced equation for this reaction. Calculate the quantity of heat produced in experiment 1, stating your units. Use relevant data from the Data Booklet and assume that all solutions have the same specific heat capacity as water. Use your answer to to calculate the enthalpy change per mole of K2CO3. Give your answer in kJ mol–1 and include a sign in your answer. Explain why the hydrochloric acid must be in an excess. For Examiner’s Use experiment 2 The experiment was repeated with 0.0200 mol of potassium hydrogencarbonate, KHCO3. All other conditions were the same. In the second experiment, the temperature fell from 21.0 °C to 17.3 °C. Construct a balanced equation for this reaction. Calculate the quantity of heat absorbed in experiment 2. Use your answer to to calculate the enthalpy change per mole of KHCO3. Give your answer in kJ mol–1 and include a sign in your answer. When KHCO3 is heated, it decomposes into K2CO3, CO2 and H2O. 2KHCO3 K2CO3 + CO2 + H2O Use Hess’ Law and your answers to and to calculate the enthalpy change for this reaction. Give your answer in kJ mol–1 and include a sign in your answer.
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
5. Chemical energetics  →  5.2. Hess’s law
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For Examiner’s Use But-1-ene, CH3CH2CH=CH2, is an important compound in the petrochemical industry. Some reactions of but-1-ene are given below. In each empty box, draw the structural formula of the organic compound formed. CH3CH2CH=CH2 V W T U H2OMnO4 – / H+ hot, concentrated MnO4 – / H+ cold, dilute Cr2O7 2– / H+ heat under reflux H3PO4 catalyst For Examiner’s Use Compound T reacts with compound U. Draw the displayed formula of the organic product of this reaction.
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
14. Hydrocarbons  →  14.2. Alkenes
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For Examiner’s Use Astronomers using modern telescopes of various types have found many molecules in the dust clouds in space. Many of these molecules are those of organic compounds and astronomers constantly look for evidence that amino acids such as aminoethanoic acid, H2NCH2CO2H, are present. One molecule that has been found in the dust clouds is hydroxyethanal, HOCH2CHO. Hydroxyethanal contains two functional groups. Name, as fully as you can, each of the functional groups present in hydroxyethanal. For each functional group, identify a reagent that will react with this group and not react with the other functional group present. In each case, describe what would be observed when this reaction is carried out. functional group 1 reagent observation functional group 2 reagent observation Give the skeletal formulae of the organic compounds formed when hydroxyethanal is reacted separately with the following. NaBH4 Cr2O7 2–/H+ under reflux conditions For Examiner’s Use In a school or college laboratory, it is possible to convert a sample of hydroxyethanal into aminoethanoic acid in a three-step process. HOCH2CHO step 1 X step 2 Y step 3 H2NCH2CO2H By considering the possible reactions of the functional groups present in hydroxyethanal, you are to deduce a possible route for this conversion. In the boxes below, draw the structural formulae of your suggested intermediates X and Y. X Y State the reagents for each of the three steps you have chosen. step 1 step 2 step 3
21. Organic synthesis  →  21.1. Organic synthesis
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