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Carboxylic Acids and Esters – Questions
Q1.The triester, T, shown below is found in palm oil. When T is heated with an excess of sodium hydroxide solution, the alcohol glycerol is formed together with a mixture of three other products as shown in the following equation.
(a) (i) Give the IUPAC name for glycerol.
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(ii) Give a use for the mixture of sodium salts formed in this reaction.
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(b) When T is heated with an excess of methanol, glycerol is formed together with a mixture of methyl esters.
(i) Give a use for this mixture of methyl esters.
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(ii) One of the methyl esters in the mixture has the IUPAC namemethyl (Z)-octadec-9-enoate. Draw two hydrogen atoms on the diagram below to illustrate the meaning of the letter Z in the name of this ester.
(1)
(iii) One of the other methyl esters in the mixture has the formula CH3(CH2)12COOCH3
Write an equation for the complete combustion of one molecule of this ester.
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(Total 5 marks)
Q2.Butenedioic acid, HOOCCH=CHCOOH, occurs as two stereoisomers. One of the isomers readily forms the acid anhydride C4H2O3 when warmed.
(a) Draw the structures of the two isomers of butenedioic acid and name the type of isomerism shown.Use the structures of the two isomeric acids to suggest why only one of them readily forms an acid anhydride when warmed. Draw the structure of the acid anhydride formed.
(6)
(b) Identify one electrophile which will react with butenedioic acid and outline a mechanism for this reaction.
(4)
(c) Write an equation for a reaction which occurs when butenedioic acid is treated with an excess of aqueous sodium hydroxide.
(2)
(d) Describe and explain the appearance of the proton n.m.r. spectrum of butenedioic acid.
(3)(Total 15 marks)
Q3.Summarised directions for recording responses to multiple completion
questions
A(i), (ii) and (iii)
only
B(i) and (iii) only
C(ii) and (iv) only
D(iv) alone
Products from the acid hydrolysis of the ester CH3CH2COOCH2CH3 include
(i) CH3CH2COOH
(ii) CH3COOH
(iii) CH3CH2OH
(v) CH3CH2CH2OH(Total 1 mark)
Q4.Three sections of the proton n.m.r. spectrum of CH3CHClCOOH are shown below.
(a) Name the compound CH3CHClCOOH
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(b) Explain the splitting patterns in the peaks at δ 1.72 and δ 4.44
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(c) Predict the splitting pattern that would be seen in the proton n.m.r. spectrum of the isomeric compound ClCH2CH2COOH
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(d) The amino acid alanine is formed by the reaction of CH3CHClCOOH with an excess of ammonia. The mechanism is nucleophilic substitution. Outline this mechanism, showing clearly the structure of alanine.
(5)
(e) The amino acid lysine has the structure
Draw structures to show the product formed in each case when lysine reacts with
(i) an excess of aqueous HCl,
(ii) an excess of aqueous NaOH,
(iii) another molecule of lysine.
(3)
(Total 12 marks)
Q5.(a) Consider the following pair of isomers.
(i) Name compound C.
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(ii) Identify a reagent which could be used in a test-tube reaction to distinguish between C and D. In each case, state what you would observe.
Reagent ______________________________________________________
Observation with C ______________________________________________
Observation with D______________________________________________(4)
(b) Consider the following pair of isomers.
(i) Name compound E.
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(ii) Identify a reagent which could be used in a test-tube reaction to distinguish between E and F. In each case, state what you would observe.
Reagent ______________________________________________________
Observation with E ______________________________________________
Observation with F______________________________________________(4)
(c) Draw the structure of the chain isomer of F which shows optical isomerism.
(1)
(Total 9 marks)
Q6.(a) The gaseous reactants W and X were sealed in a flask and the mixture left until the
following equilibrium had been established.
2W(g) + X(g) 3Y(g) + 2Z(g) ΔH = –200 kJ mol–1
Write an expression for the equilibrium constant, Kp, for this reaction.State one change in the conditions which would both increase the rate of reaction and decrease the value of Kp. Explain your answers.
(7)
(b) Ethyl ethanoate can be prepared by the reactions shown below.
Reaction 1CH3COOH(l) + C2H5OH(l) CH3COOC2H5(l) + H2O(l) ∆H = –2.0 kJ mol–1
Reaction 2CH3COCl(l) + C2H5OH(l) → CH3COOC2H5(l) + HCl(g) ∆H = –21.6 kJ mol–1
(i) Give one advantage and one disadvantage of preparing ethyl ethanoate by Reaction 1 rather than by Reaction 2.
(ii) Use the information given above and the data below to calculate values for the standard entropy change, ∆S , and the standard free-energy change, ∆G , for Reaction 2 at 298 K.
CH3COCl(l) C2H5OH(l) CH3COOC2H5(l) HCl(g)
S /JK1mol1 201 161 259 187
(8)(Total 15 marks)
Q7.(a) Describe how propanal, CH3CH2CHO, and propanone, CH3COCH3, can be
distinguished using
(i) a chemical test and
(ii) the number of peaks in their proton n.m.r. spectra.(5)
(b) Compound Z can be produced by the reaction of compound X with compound Y as shown in the synthesis outlined below.
Identify compounds X and Y.For each of the three steps in the synthesis, name the type of reaction involved and give reagents and conditions. Equations are not required.
(10)(Total 15 marks)
Q8.A four-step synthesis of compound T is shown.
(a) Give the reagent and conditions for Step 1.State how you could obtain a sample of the alcohol from the reaction mixture formed in Step 1.
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(b) Draw the structure of compound S.For each of Steps 3 and 4, give a reagent and one condition, other than heat.
(5)(Total 8 marks)
Q9.(a) Compound A, HCOOCH2CH2CH3, is an ester. Name this ester and write an equation
for its reaction with aqueous sodium hydroxide.
Name _____________________________________________________________
Equation ___________________________________________________________(2)
(b) The initial rate of reaction between ester A and aqueous sodium hydroxide was measured in a series of experiments at a constant temperature. The data obtained
are shown below.
Experiment Initial concentration of NaOH / mol dm–3
Initial concentration of A
/ mol dm–3
Initial rate/ mol dm–3 s–1
1 0.040 0.030 4.0 × 10–4
2 0.040 0.045 6.0 × 10–4
3 0.060 0.045 9.0 × 10–4
4 0.120 0.060 to be calculated
Use the data in the table to deduce the order of reaction with respect to A and the order of reaction with respect to NaOH. Hence calculate the initial rate of reaction in Experiment 4.
Order with respect to A ________________________________________________
Order with respect to NaOH ____________________________________________
Initial rate in Experiment 4 _____________________________________________
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(c) In a further experiment at a different temperature, the initial rate of reaction was found to be 9.0 × 10–3 mol dm–3 s–1 when the initial concentration of A was 0.020 mol dm–3 and the initial concentration of NaOH was 2.00 mol dm–3.Under these new conditions with the much higher concentration of sodium hydroxide, the reaction is first order with respect to A and appears to be zero order with respect to sodium hydroxide.
(i) Write a rate equation for the reaction under these new conditions.
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(ii) Calculate a value for the rate constant under these new conditions and state its units.
Calculation _____________________________________________________
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Units _________________________________________________________
(iii) Suggest why the order of reaction with respect to sodium hydroxide appears to be zero under these new conditions.
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(d) A naturally-occurring triester, shown below, was heated under reflux with an excess of aqueous sodium hydroxide and the mixture produced was then distilled. One of the products distilled off and the other was left in the distillation flask.
(i) Draw the structure of the product distilled off and give its name.
Structure
Name _________________________________________________________
(ii) Give the formula of the product left in the distillation flask and give a use for it.
Formula _______________________________________________________
Use __________________________________________________________(4)
(Total 15 marks)
Q10.Esters have many important commercial uses such as solvents and artificial flavourings in foods.
Esters can be prepared in several ways including the reactions of alcohols with carboxylic acids, acid anhydrides, acyl chlorides and other esters.
(a) Ethyl butanoate is used as a pineapple flavouring in sweets and cakes.
Write an equation for the preparation of ethyl butanoate from an acid and an alcohol.
Give a catalyst used for the reaction.
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(b) Butyl ethanoate is used as a solvent in the pharmaceutical industry.
Write an equation for the preparation of butyl ethanoate from an acid anhydride and an alcohol.
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(c) Name and outline a mechanism for the reaction of CH3COCl with CH3OH to form an ester.
(5)
(d) The ester shown below occurs in vegetable oils. Write an equation to show the formation of biodiesel from this ester.
CH2OOCC17H31
│CHOOCC17H33
│CH23OOCC17H29
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(e) Draw the repeating unit of the polyester Terylene that is made from benzene-1,4-dicarboxylic acid and ethane-1,2-diol.
Although Terylene is biodegradeable, it is preferable to recycle objects made from Terylene.
Give one advantage and one disadvantage of recycling objects made from Terylene.
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(Total 19 marks)
Q11.Consider the sequence of reactions below.
(a) Name and outline a mechanism for Reaction 1.
Name of mechanism _________________________________________________
Mechanism
(5)
(b) (i) Name compound Q
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(ii) The molecular formula of Q is C4H7NO. Draw the structure of the isomer of Q which shows geometrical isomerism and is formed by the reaction of ammonia with an acyl chloride.
(3)
(c) Draw the structure of the main organic product formed in each case when R reacts separately with the following substances:
(i) methanol in the presence of a few drops of concentrated sulphuric acid;
(ii) acidified potassium dichromate(VI);
(iii) concentrated sulphuric acid in an elimination reaction.
(3)
(Total 11 marks)
Q12.(a) Write an equation for the formation of methyl propanoate, CH3CH2COOCH3, from
methanol and propanoic acid.
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(b) Name and outline a mechanism for the reaction between methanol and propanoyl chloride to form methyl propanoate.
Name of mechanism _________________________________________________
Mechanism
(5)
(c) Propanoic anhydride could be used instead of propanoyl chloride in the preparation of methyl propanoate from methanol. Draw the structure of propanoic anhydride.
(1)
(d) (i) Give one advantage of the use of propanoyl chloride instead of propanoic acid in the laboratory preparation of methyl propanoate from methanol.
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(ii) Give one advantage of the use of propanoic anhydride instead of propanoyl chloride in the industrial manufacture of methyl propanoate from methanol.
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(e) An ester contains a benzene ring. The mass spectrum of this ester shows a molecular ion peak at m/z = 136.
(i) Deduce the molecular formula of this ester.
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(ii) Draw two possible structures for this ester.
(3)(Total 12 marks)
Q13.Salicylic acid, C6H4(OH)COOH, reacts with magnesium to produce magnesium salicylate and hydrogen.
(a) Complete the equation for this reaction.
C6H4(OH)COOH(1)
(b) In an alternative method for determining percentage purity, a student reacted a solution of salicylic acid with an excess of magnesium and collected the hydrogen gas that was released.
Complete the diagram below to show an apparatus that could be used to collect and measure the volume of hydrogen gas produced.
(1)
(Total 2 marks)
Q14.(a) Propanoic acid can be made from propan-1-ol by oxidation using acidified
potassium dichromate(VI). Propanal is formed as an intermediate during this oxidation.
(i) State the colour of the chromium species after the potassium dichromate(VI) has reacted.
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(ii) Describe the experimental conditions and the practical method used to ensure that the acid is obtained in a high yield. Draw a diagram of the assembled apparatus you would use.
Conditions _____________________________________________________
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Apparatus
(4)
(iii) Describe the different experimental conditions necessary to produce propanal in high yield rather than propanoic acid.
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(b) Propan-1-ol is a volatile, flammable liquid. Give one safety precaution that should be used during the reaction to minimise this hazard.
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(c) A student followed the progress of the oxidation of propan-1-ol to propanoic acid by extracting the organic compounds from one sample of reaction mixture.
(i) Give a chemical reagent which would enable the student to confirm the presence of propanal in the extracted compounds. State what you would observe when propanal reacts with this reagent.
Reagent _______________________________________________________
Observation ____________________________________________________
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(ii) Give a chemical reagent that would enable the student to confirm the presence of propanoic acid in the extracted compounds. State what you would observe when propanoic acid reacts with this reagent.
Reagent _______________________________________________________
Observation ____________________________________________________
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(d) Predict which one of the compounds, propan-1-ol, propanal and propanoic acid will have the highest boiling point. Explain your answer.
Prediction __________________________________________________________
Explanation _________________________________________________________
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(Total 15 marks)
Q15.Synthesis gas is a mixture of carbon monoxide and hydrogen. Methanol can be manufactured from synthesis gas in a reversible reaction as shown by the following equation.
CO(g) + 2H2(g) CH3OH(g) ΔHο = –91 kJ mol–1
(a) A sample of synthesis gas containing 0.240 mol of carbon monoxide and 0.380 mol of hydrogen was sealed together with a catalyst in a container of volume 1.50 dm3.When equilibrium was established at temperature T1 the equilibrium mixture contained 0.170 mol of carbon monoxide.
Calculate the amount, in moles, of methanol and the amount, in moles, of hydrogen in the equilibrium mixture.
Methanol __________________________________________________________
Hydrogen __________________________________________________________(2)
(b) A different sample of synthesis gas was allowed to reach equilibrium in a similar container of volume 1.50 dm3 at temperature T1
At equilibrium, the mixture contained 0.210 mol of carbon monoxide, 0.275 mol of hydrogen and 0.0820 mol of methanol.
(i) Write an expression for the equilibrium constant Kc for this reaction.
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(ii) Calculate a value for Kc for the reaction at temperature T1 and state its units.
Calculation _____________________________________________________
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Units _________________________________________________________
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(iii) State the effect, if any, on the value of Kc of adding more hydrogen to the equilibrium mixture.
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(c) The temperature of the mixture in part (b) was changed to T2 and the mixture was left to reach a new equilibrium position. At this new temperature the equilibrium concentration of methanol had increased.
Deduce which of T1 or T2 is the higher temperature and explain your answer.
Higher temperature ___________________________________________________
Explanation _________________________________________________________
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(d) The following reaction has been suggested as an alternative method for the production of methanol.
CO2(g) + 3H2(g) CH3OH(g) + H2O(g)
The hydrogen used in this method is obtained from the electrolysis of water.
Suggest one possible environmental disadvantage of the production of hydrogen by electrolysis.
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(e) One industrial use of methanol is in the production of biodiesel from vegetable oils such as
Give the formula of one compound in biodiesel that is formed by the reaction of methanol with the vegetable oil shown above.
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(Total 13 marks)
Q16.Esters are used as raw materials in the production of soaps and biodiesel.
(a) A student prepared an ester by two different methods.
Method 1 alcohol + acid anhydride
Method 2 alcohol + acyl chloride
(i) An ester was prepared using method 1, by reacting (CH3)2CHOH with (CH3CO)2O
Write an equation for this reaction and give the IUPAC name of the ester formed.
Equation
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IUPAC name of the ester __________________________________________(2)
(ii) The same ester was prepared using method 2 by reacting (CH3)2CHOH with CH3COCl
Outline a mechanism for this reaction.
(4)
(b) The ester shown occurs in vegetable oils.It can be hydrolysed to make soap and can also be used to produce biodiesel.
(i) Write an equation for the reaction of this ester with sodium hydroxide to form soap.
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(ii) Give the formula of the biodiesel molecule with the highest Mr that can be produced by reaction of this ester with methanol.
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(Total 9 marks)
Q17.The slowing down of chemical processes is important in food storage. Over time, fats may become rancid. This involves the formation of compounds that have unpleasant odours and flavours within the food. Hydrolysis of fats is one way in which rancid flavours are formed. Fats break down to long-chain carboxylic (fatty) acids and glycerol.
(a) Complete the right-hand side of the equation below to show how hydrolysis affects the molecule of fat shown.
+ 3H2O → 3 ........................ + ........................(2)
(b) Other than by cooling, suggest one method that would decrease the rate of hydrolysis of fats.
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(c) Food can also acquire unpleasant flavours when the fatty acids, produced by hydrolysis of fats, are oxidised by air. This oxidation occurs by a free-radical mechanism. Chemicals called anti-oxidants can be added to food to slow down the oxidation. Suggest why anti-oxidants are not regarded as catalysts.
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(d) A student investigated the extent of hydrolysis in an old sample of the fat in part (a). The carboxylic acid extracted from a 2.78 g sample of this fat (Mr = 806.0) reacted with 24.5 cm3 of a 0.150 mol dm–3 solution of NaOH. Calculate the percentage of the fat that had hydrolysed. Show your working.
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(Total 9 marks)
Q18.The reactions of molecules containing the chlorine atom are often affected by other functional groups in the molecule.
Consider the reaction of CH3CH2COCl and of CH3CH2CH2Cl with ammonia.
(a) For the reaction of CH3CH2COCl with ammonia, name and outline the mechanism and name the organic product.
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(Extra space) ________________________________________________________
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(b) For the reaction of CH3CH2CH2Cl with an excess of ammonia, name and outline the mechanism and name the organic product.
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(c) Suggest one reason why chlorobenzene (C6H5Cl) does not react with ammonia under normal conditions.
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(Total 13 marks)
Q19.This question is about some isomers of C5H8O2
(a) Compound H is a cyclic ester that can be prepared as shown.
On the structure of H, two of the carbon atoms are labelled.
HOCH2CH2CH2CH2COCl + HCL
H
(i) Name and outline a mechanism for this reaction.
Use Table C on the Data Sheet to give the 13C n.m.r. δ value for the carbon atom labelled a and the δ value for the carbon atom labelled b.
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(ii) HOCH2CH2CH2CH2COCl can also react to form a polyester in a mechanism similar to that in part (i).
Draw the repeating unit of the polyester and name the type of polymerisation involved.
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(b) State how you could distinguish between compounds J and K by a simple test-tube reaction.
State how you could distinguish between J and K by giving the number of peaks in the 1H n.m.r. spectrum of each compound.
J K
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(c) Draw the structure of each of the following isomers of C5H8O2
Label each structure you draw with the correct letter L, M, N, P or Q.
L is methyl 2-methylpropenoate.
M is an ester that shows E-Z stereoisomerism.
N is a carboxylic acid with a branched carbon chain and does not show stereoisomerism.
P is an optically active carboxylic acid.
Q is a cyclic compound that contains a ketone group and has only two peaks in its 1H n.m.r. spectrum.
(5)
(Total 19 marks)
Q20.Esters are produced by the reaction of alcohols with other esters and by the reaction of alcohols with carboxylic acids.
(a) The esters which make up biodiesel are produced industrially from the esters in vegetable oils.
(i) Complete the equation for this formation of biodiesel.
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(ii) Write an equation for the complete combustion of C17H35COOCH3.
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(b) The ester commonly known as diethyl malonate (DEM) occurs in strawberries and grapes. It can be prepared from acid A according to the following equilibrium.
(i) A mixture of 2.50 mol of A and 10.0 mol of ethanol was left to reach equilibrium in an inert solvent in the presence of a small amount of concentrated sulfuric acid.The equilibrium mixture formed contained 1.80 mol of DEM in a total volume, V dm3, of solution.
Calculate the amount (in moles) of A, of ethanol and of water in this equilibrium mixture.
Moles of A ____________________________________________________
Moles of ethanol _______________________________________________
Moles of water _________________________________________________(3)
(ii) The total volume of the mixture in part (b)(i) was doubled by the addition of more of the inert solvent.
State and explain the effect of this addition on the equilibrium yield of DEM.
Effect _________________________________________________________
Explanation ____________________________________________________
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(iii) Using A to represent the acid and DEM to represent the ester, write an expression for the equilibrium constant Kc for the reaction.
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(iv) In a second experiment, the equilibrium mixture was found to contain 0.85 mol of A, 7.2 mol of ethanol, 2.1 mol of DEM and 3.4 mol of water.
Calculate a value of Kc for the reaction and deduce its units.
Calculation ____________________________________________________
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Units _________________________________________________________
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(Total 13 marks)
Q21.Ibuprofen is a drug used as an alternative to aspirin for the relief of pain, fever and inflammation. The structure of ibuprofen is shown below.
Which one of the following statements is not correct?
A It has optical isomers.
B It liberates carbon dioxide with sodium carbonate solution.
D It undergoes esterification with ethanol.
D It undergoes oxidation with acidified potassium dichromate(VI).(Total 1 mark)
Q22.Which one of the following is not a correct general formula for the non-cyclic compounds listed?
A alcohols CnH2n+2O
B aldehydes CnH2n+1O
C esters CnH2nO2
C primary amines CnH2n+3N(Total 1 mark)
Q23.For this question refer to the reaction scheme below.
Which one of the following statements is not correct?
A Reaction of W with sodium cyanide followed by hydrolysis of the resulting product gives propanoic acid.
B Mild oxidation of Z produces a compound that reacts with Tollens’ reagent, forming a silver mirror.
C Z reacts with ethanoic acid to produce the ester propyl ethanoate.
C W undergoes addition polymerisation to form poly(propene).(Total 1 mark)
Q24.Butan-1-ol was converted into butyl propanoate by reaction with an excess of propanoic acid. In the reaction, 6.0 g of the alcohol gave 7.4 g of the ester. The percentage yield of ester was
A 57
B 70
C 75
D 81(Total 1 mark)
Q25.Which compound is formed by the reaction of ethane-1,2-diol with an acid?
A
B
C
D CH3CH2 — O — CH2CH2OH(Total 1 mark)
Q26.The structural formula of ethyl 2-methylpropanoate is
A
B
C
D (Total 1 mark)
Q27.An excess of methanol was mixed with 12 g of ethanoic acid and an acid catalyst. At equilibrium the mixture contained 8 g of methyl ethanoate. The percentage yield of ester present was
A 11
B 20
C 54
D 67(Total 1 mark)
Q28.
Acid hydrolysis of produces
A CH3CH(OH)CH2CH2COOH
B CH2(OH)CH2CH2CH2COOH
C CH3CH(OH)CH2CH2OCHO
D CH2(OH)CH2CH2CH2OCHO(Total 1 mark)
Q29.Propanoic acid reacts with methanol in the presence of a small amount of concentrated sulphuric acid. The empirical formula of the ester formed is
A CH2O
B C2H6O2
C C2H4O2
D C2H4O(Total 1 mark)
Q30.Hydrolysis of the ester, CH3COOCH2CH2CH3, produces ethanoic acid. In an experiment, 2.04 g of the ester was used and 0.90 g of ethanoic acid was produced. The percentage yield of ethanoic acid was:
A 44
B 59
C 75
D 90(Total 1 mark)
Q31.Summarised directions for recording responses to multiple completion
questions
A(i), (ii) and (iii)
only
B(i) and (iii) only
C(ii) and (iv) only
D(iv) alone
Isomers of the ester HCOOCH2CH2CH3, include
(i) ethyl ethanoate
(ii) methyl propanoate
(iii) butanoic acid
(iv) butyl methanoate(Total 1 mark)
Q32.How many structural isomers, which are esters, have the molecular formula C4H8O2?
A 2
B 3
C 4
D 5(Total 1 mark)
Q33.Which one of the following is not a correct statement about vitamin C, shown below?
A It is a cyclic ester.
B It can form a carboxylic acid on oxidation.
C It decolourises a solution of bromine in water.
D It is a planar molecule.(Total 1 mark)