9701_s11_qp_22 - revisedeck

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Ethanoic acid can be reacted with alcohols to form esters, an equilibrium mixture being formed. CH3CO2H + ROH CH3CO2R + H2O The reaction is usually carried out in the presence of an acid catalyst. Write an expression for the equilibrium constant, Kc, for this reaction, clearly stating the units. Kc = units In an experiment to determine Kc a student placed together in a conical flask 0.10 mol of ethanoic acid, 0.10 mol of an alcohol ROH, and 0.005 mol of hydrogen chloride catalyst. The flask was sealed and kept at 25 °C for seven days. After this time, the student titrated all of the contents of the flask with 2.00 mol dm–3 NaOH using phenolphthalein indicator. At the end-point, 22.5 cm3 of NaOH had been used. Calculate the amount, in moles, of NaOH used in the titration. What amount, in moles, of this NaOH reacted with the hydrogen chloride? Write a balanced equation for the reaction between ethanoic acid and NaOH. Hence calculate the amount, in moles, of NaOH that reacted with the ethanoic acid. For Examiner’s Use Use your results from to calculate the amount, in moles, of ethanoic acid present at equilibrium. Hence complete the table below. CH3CO2H ROH CH3CO2R H2O initial amount / mol 0.10 0.10 equilibrium amount / mol Use your results to calculate a value for Kc for this reaction. Esters are hydrolysed by sodium hydroxide. During the titration, sodium hydroxide reacts with ethanoic acid and the hydrogen chloride, but not with the ester. Suggest a reason for this. What would be the effect, if any, on the amount of ester present if all of the water were removed from the flask and the flask kept for a further week at 25 °C? Explain your answer.

7. Equilibria → 7.1. Chemical equilibria: reversible reactions, dynamic equilibrium

18. Carboxylic acids and derivatives → 18.2. Esters

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For Examiner’s Use Halogenoalkanes have been widely used as aerosol propellants, refrigerants and solvents for many years. Fluoroethane, CH3CH2F, has been used as a refrigerant. It may be made by reacting ethene with hydrogen fluoride. You are to calculate a value for the C–F bond energy in fluoroethane. Use relevant bond energies from the Data Booklet, and the equation below to calculate a value for the bond energy of the C–F bond. CH2 = CH2+ HFCH3CH2FΔH o = – 73 kJ mol–1 C–F bond energy = kJ mol–1 Another halogenoalkane which was used as a refrigerant, and also as an aerosol propellant, is dichlorodifluoromethane, CCl2F2. State two reasons why compounds such as CH3CH2F and CCl2F2 have been used as aerosol propellants and refrigerants. For Examiner’s Use CCl2F2 is one of many chlorofluorocarbon compounds responsible for damage to the ozone layer in the stratosphere. By using relevant data from the Data Booklet, and your answer to suggest why CCl2F2 is responsible for damage to the ozone layer in the stratosphere whereas CH3CH2F is not. Both CH3CH2F and CCl2F2 are greenhouse gases. The ‘enhanced greenhouse effect’ is of great concern to the international community. What is meant by the term enhanced greenhouse effect? Water vapour is the most abundant greenhouse gas. What is the second most abundant greenhouse gas? A greenhouse gas which is present in very small amounts in the atmosphere is sulfur hexafluoride, SF6, which is used in high voltage electrical switchgear. What shape is the SF6 molecule?

15. Halogen compounds → 15.1. Halogenoalkanes

3. Chemical bonding → 3.4. Covalent bonding and coordinate (dative covalent) bonding

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For Examiner’s Use Barium, proton number 56, is a Group II element which occurs in nature as the carbonate or sulfate. The element was first isolated by Sir Humphry Davy in 1808. Some reactions of barium and its compounds are shown in the reaction scheme below. BaRheat gently in oxygen H2OUSTdilute HCl dilute H2SO4 dilute HNO3 reaction 1 WNa2CO3VState the formula of each of the barium compounds R to W. R S T U V W Write balanced equations for the following reactions. compound T to compound W the roasting of V in air For Examiner’s Use Suggest a gaseous reagent for the conversion of T into V and write a balanced equation for the reaction. reagent equation Suggest the formula of an aqueous reagent, other than an acid, for reaction 1. ……………………… When barium is heated strongly in oxygen, an oxide X is formed. The oxide X contains 18.9% of oxygen by mass. The oxide X reacts with dilute sulfuric acid in a 1:1 ratio. Two products, one insoluble and one soluble, are formed. BaXheat strongly in oxygen Y+ dilute H2SO4 Z+ Calculate the empirical formula of X. Suggest the identity of the solid Y. Use your answers to and to construct an equation for the reaction of X with H2SO4.

10. Group 2 → 10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds

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For Examiner’s Use Chlorine is manufactured by electrolysis from brine, concentrated aqueous sodium chloride. Describe, with the aid of a fully labelled diagram, the industrial electrolysis of brine in a diaphragm cell. State what each electrode is made of and show clearly the inlet for the brine and the outlets for the products. Write a half-equation, with state symbols, for the reaction at each electrode. anode cathode Name the chemical that is produced in solution in this electrolytic process.

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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For Examiner’s Use Although there are many different types of food eaten around the world, animal fats and/or vegetable oils are commonly used in cooking. Animal fats and vegetable oils are usually glyceryl esters, that is esters of glycerol, propane-1,2,3-triol. CH2OH ⏐ CHOH ⏐ CH2OH Many animal fats contain esters of stearic acid, CH3(CH2)16CO2H. Vegetable oils often contain esters of oleic acid, CH3(CH2)7CHCH(CH2)7CO2H. Draw the structural formula of the glyceryl ester formed when one molecule of glycerol is completely esterified with stearic acid. What reagentwould you use, in a school or college laboratory, to obtain a small sample of oleic acid, C17H33CO2H, from the glyceryl ester present in a vegetable oil? Oleic acid is the cis isomer and elaidic acid the trans isomer of CH3(CH2)7CHCH(CH2)7CO2H. By using this formula, draw the structural formula of elaidic acid, clearly showing the stereochemistry. For Examiner’s Use Oleic and elaidic acids are examples of mono-unsaturated acids. Many vegetable oils contain esters of polyunsaturated fatty acids. Such oils are often hydrogenated to form esters containing saturated or mono-unsaturated fatty acids. Suggest the meaning of the term polyunsaturated fatty acid. What reagent and conditionare used for the hydrogenation of an unsaturated fatty acid? reagent condition In cooking, unsaturated fats are often oxidised to give aldehydes or ketones. Give the structural formulae of the two aldehydes formed by the partial oxidation of the unsaturated fat below. In the structure, X, represents the rest of the fat molecule. CH3(CH2)7CHCH(CH2)7X Name the reagent you would use to show that the product contained either an aldehyde or a ketone. What change would be seen? reagent observation What reagent would you use to confirm the presence of an aldehyde? What change would be seen? reagent observation For Examiner’s Use Animal fats and vegetable oils can become rancid because of oxidation. The rancid fat or oil has an unpleasant smell and taste. Antioxidants are used to prevent the spoilage of many foodstuffs by oxidation. One antioxidant that is widely used is vitamin C, ascorbic acid. HO HO H O O ascorbic acid OH HO How many chiral carbon atoms are present in one molecule of ascorbic acid? If none, write ‘none’. The ascorbic acid molecule contains three functional groups. Two of these are alcohol (primary and secondary) and alkene. What is the name of the third functional group?

18. Carboxylic acids and derivatives → 18.2. Esters

16. Hydroxy compounds → 16.1. Alcohols

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