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Alcohols 1
Name: ________________________
Class: ________________________
Date: ________________________
Time: 357 minutes
Marks: 340 marks
Comments:
At minimum complete:
Alcohols 1:
Question 1 (7 marks)
[skeletal formula, oxidation equation, diagram for reflux, anti-bumping
granules]
Question 2 (15 marks)
[fermentation, carbon neutrality, bond enthalpies, calorimetry]
Question 8 (15 marks)
[isomerism, infrared spectrometry, biofuels, oxidation equation and
observation with dichromate]
Question 26 (5 marks)
[practical question]
Total 42 marks.
Q1. Propane-1,2-diol has the structure CH 2 (OH)CH(OH)CH 3. It is used to make polyesters and is one of the main substances in electronic cigarettes (E-cigarettes).
A sample of propane-1,2-diol was refluxed with a large excess of potassium dichromate(VI) and sulfuric acid.
(a) Draw the skeletal formula of propane-1,2-diol.
(1)
(b) Write an equation for this oxidation reaction of propane-1,2-diol under reflux, using [O] to represent the oxidizing agent.
Show the displayed formula of the organic product.
(2)
(c) Draw a labelled diagram to show how you would set up apparatus for refluxing.
(2)
(d) Anti-bumping granules are placed in the flask when refluxing. Suggest why these granules prevent bumping.
(4)
(b) It has been claimed that there is no net carbon (greenhouse gas) emission to the atmosphere when ethanol made by Process 2 is used as a fuel.
State the term that is used to describe fuels of this type.
Use the equations for Processes 1, 2 and 3 to show why it can be claimed that there is no net emission of carbon-containing greenhouse gases.
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(c) Use the information from the equation for Process 3 above and the mean bond enthalpies from the table below to calculate a value for the enthalpy change for this process.
C–H C–C C–O O–H C=O O=O
Mean bond enthalpy / kJ mol–1^ +412^ +348^ +360^ +463^ +743^ +
Give one reason why the value calculated from mean bond enthalpies is different from the value given in a data book.
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(4)
(d) A student carried out a simple laboratory experiment to measure the enthalpy change for Process 3. The student showed that the temperature of 200 g of water increased by 8.0 °C when 0.46 g of pure ethanol was burned in air and the heat produced was used to warm the water.
Use these results to calculate the value, in kJ mol–1, obtained by the student for this enthalpy change. (The specific heat capacity of water is 4.18 J K –1^ g–1)
Give one reason, other than heat loss, why the value obtained from the student’s results is less exothermic than a data book value.
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Q3. There are seven isomeric carbonyl compounds with the molecular formula C 5 H 10 O. The structures and names of some of these isomers are given below.
Structure Name
pentanal
2-methybutanal
(c) Pentanal can be formed by the oxidation of an alcohol.
(i) Identify this alcohol.
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(ii) State the class to which this alcohol belongs.
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Q4. (a) Alcohols can be classed as primary, secondary or tertiary. Draw possible structures for a primary, a secondary and a tertiary alcohol which have the molecular formula C 4 H 8 O. Which of the structures you have drawn cannot be oxidised by potassium dichromate in acid solution? (4)
(b) Explain what is meant by the fingerprint region of an infra-red spectrum. State how it is used to confirm the identity of organic molecules such as the primary, secondary and tertiary alcohols of molecular formula C 4 H 8 O. (2)
(c) Each of the parts below concerns a different pair of isomers. Deduce one possible structural formula for each of the species A to F. Use, where appropriate, the table of infra-red absorption data given on the data sheet.
(i) A and B have the molecular formula C 3 H 8 O. A has a broad absorption band at 3300 cm–1^ in its infra-red spectrum, but B does not.
(ii) C and D have the molecular formula C 5 H 10. C has a weak absorption band at 1650 cm–1^ in its infra-red spectrum, but D does not.
(iii) E and F have the molecular formula C 3 H 6 O and both have strong absorption bands at about 1700 cm –1^ in their infra-red spectra. E reacts with Tollens’ reagent but F does not. (6) (Total 12 marks)
Q5. In an investigation of the chemical properties of alcohols, a mixture of ethanol and acidified potassium dichromate(VI) is heated in a conical flask in a water bath.
(a) Explain why a water bath is used to heat the mixture.
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(b) Describe the colour change which would be observed.
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Q6. Carbon monoxide and hydrogen are used in the manufacture of methanol. An equilibrium is established according to the following equation.
Cu catalyst CO(g) + 2H 2 (g) CH 3 OH(g) ∆ H = –9l kJ mol–
(a) Give two features of a reaction at equilibrium.
Feature 1 .....................................................................................................
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Feature 2 ......................................................................................................
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(b) Explain why an increase in temperature causes a decrease in the equilibrium yield of methanol.
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Q7. Consider the following scheme of reactions.
(a) State the type of structural isomerism shown by propanal and propanone.
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(b) A chemical test can be used to distinguish between separate samples of propanal and propanone.
Identify a suitable reagent for the test. State what you would observe with propanal and with propanone.
Test reagent...................................................................................................
Observation with propanal............................................................................
Observation with propanone......................................................................... (3)
(c) State the structural feature of propanal and propanone which can be identified from their infrared spectra by absorptions at approximately 1720 cm –1.
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(d) The reaction of chlorine with propane is similar to the reaction of chlorine with methane.
(i) Name the type of mechanism in the reaction of chlorine with methane.
(1)
(ii) Write an equation for each of the following steps in the mechanism for the reaction of chlorine with propane to form l-chloropropane (CH 3 CH 2 CH 2 Cl).
Initiation step
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First propagation step
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Second propagation step
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A termination step to form a molecule with the empirical formula C 3 H 7
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(e) High resolution mass spectrometry of a sample of propane indicated that it was contaminated with traces of carbon dioxide.
Use the data in the table to show how precise M (^) r values can be used to prove that thesample contains both of these gases.
(2) (Total 12 marks)
(3)
(c) British scientists have used bacteria to ferment glucose and produce the biofuel butan-1-ol.
Write an equation for the fermentation of glucose (C 6 H 12 O 6 ) to form butan-1-ol, carbon dioxide and water only.
State one condition necessary to ensure the complete combustion of a fuel in air.
Write an equation for the complete combustion of butan-1-ol and state why it can be described as a biofuel.
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(d) Butan-1-ol reacts with acidified potassium dichromate(VI) solution to produce two organic compounds.
State the class of alcohols to which butan-1-ol belongs.
Draw the displayed formula for both of the organic products.
State the type of reaction that occurs and the change in colour of the potassium dichromate(VI) solution.
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(5) (Total 15 marks)
Q9. Ethanol can be oxidised slowly to ethanal. State how a sample of ethanol could be tested to confirm the presence of ethanal. State what you would observe.
Test .........................................................................................................................
Observation ............................................................................................................ (Total 2 marks)
Q10. Ethanal is prepared by heating ethanol with potassium dichromate(VI) in the presence of sulfuric acid. Figures 1 and 2 show two possible ways of heating this reaction mixture.
Figure 1 Figure 2
(Total 3 marks)
Q12. A student devised an experiment to investigate the enthalpies of combustion of some alcohols. The student chose the following series of primary alcohols.
Name Formula
Methanol CH 3 OH
Ethanol CH 3 CH 2 OH
Propan-1-ol CH 3 CH 2 CH 2 OH
Butan-1-ol CH 3 CH 2 CH 2 CH 2 OH
Pentan-1-ol CH 3 CH 2 CH 2 CH 2 CH 2 OH
Alcohol X CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 OH
Heptan-1-ol CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 OH
(a) (i) Name alcohol X.
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(ii) State the general name of the type of series shown by these primary alcohols.
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(iii) Draw the displayed formula of the position isomer of butan-1-ol.
(1)
(iv) Using [O] to represent the oxidising agent, write an equation for the oxidation of butan-1-ol to form an aldehyde.
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(v) Draw the displayed formula of a functional group isomer of this aldehyde.
(1)
(b) The student carried out a laboratory experiment to determine the enthalpy change when a sample of butan-1-ol was burned. The student found that the temperature of 175 g of water increased by 8.0 °C when 5.00 × 10–3^ mol of pure butan-1-ol was burned in air and the heat produced was used to warm the water.
Use the student’s results to calculate a value, in kJ mol–1, for the enthalpy change when one mole of butan-1-ol is burned. (The specific heat capacity of water is 4.18 J K–1^ g–1)
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(c) (i) Give the meaning of the term standard enthalpy of combustion.
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(i) In terms of bonds broken and bonds formed, explain why the calculated values of enthalpies of combustion of these alcohols, when plotted against M r , follow a straight line.
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(ii) Give two reasons why the experimental values obtained by the student are lower than the calculated values using the enthalpy of formation data.
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Q13. Sulfuric acid is an important chemical in many industrial and laboratory reactions. Consider the following three reactions involving sulfuric acid.
Reaction 1 Mg(OH) 2 + H 2 SO 4 → MgSO 4 + 2H 2 O
Reaction 2 The reaction of solid sodium bromide with concentrated sulfuric acid
Reaction 3 H 2 C=CH 2 + H 2 O CH 3 CH 2 OH
(a) Give a use for magnesium hydroxide in medicine.
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(b) Sulfuric acid behaves as an oxidising agent in Reaction 2.
(i) In terms of electrons, state the meaning of the term oxidising agent.
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(ii) Give the formula of the oxidation product that is formed from sodium bromide in Reaction 2.
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(iii) Deduce the half-equation for the reduction of H 2 SO 4 to SO 2 in Reaction 2.
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(c) The formation of ethanol in Reaction 3 uses concentrated sulfuric acid and proceeds in two stages according to the following equations.
Stage 1 H 2 C=CH 2 + H 2 SO 4 → CH 3 CH 2 OSO 2 OH
Stage 2 CH 3 CH 2 OSO 2 OH + H 2 O → CH 3 CH 2 OH + H 2 SO 4
(i) State the overall role of sulfuric acid in Reaction 3.
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(ii) Outline a mechanism for Stage 1 of this reaction.
