Chemistry Exercise

8/13/2019 Chemistry Exercise

1/25

NT Exampro 1

1. (a) The enthalpy change for the reaction

CH2=CH2+ H2CH3CH3

is 120 kJ mol1, whereas that for the reduction of benzene, C6H6, to cyclohexane, C6H12,is 208 kJmol1. What may be deduced from the fact that this value is not three times

the first one?

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................(2)

(b) (i) State the conditions under which benzene may be nitrated to form

mononitrobenzene.

..........................................................................................................................

(ii) Both of the reagents that are used to nitrate benzene are usually regarded as acids.

However, in this instance, one of them behaves as a base. Show how this is so.

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

(iii) Give the mechanism for the nitration of benzene.

(iv) Explain why benzene tends to undergo substitution rather than addition reactions.

..........................................................................................................................

..........................................................................................................................

(8)(Total 10 marks)


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NT Exampro 2

2. The enthalpy change for the reaction

CH2=CH2+ H2CH3CH3

is 120 kJ mol1, whereas that for the reduction of benzene, C6H6, to cyclohexane,

C6H12, is 208 kJmol1. What may be deduced from the fact that this value is not three

times the first one?

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................(2)

3. Consider the following reaction scheme, then answer the questions which follow.

step 1 step 2 step 3

CH3 CO

OH O

A B C D

C H2 5

C

O

(a) Give the reagents and conditions for steps 1, 2 and 3.

Step 1 Reagent: ................................................................................................

Conditions: .......................................................................................................

Step 2 Reagent: .................................................................................................

Conditions: ........................................................................................................

Step 3 Reagent: ..................................................................................................

Conditions: ........................................................................................................(7)

(b) (i) Write an equation for the reaction of compound Dwith dilute aqueoussodium hydroxide.

(ii) What type of reaction is this?

..........................................................................................................................(2)

(c) Outline brieflyhow you would isolate a sample of the aromatic product of the reaction in(b)(i).


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NT Exampro 3

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................(3)

(d) Give the mechanism for the conversion of

CH3

to

(4)

(Total 16 marks)

4. Propane-1,2-diol, CH3CH(OH)CH2OH, can be used to manufacture a polymer.

(a) Give the structure of a suitable compound which could react with propane-1-2-diol toform a polymer.

(b) Give the repeat unit of the polymer formed and name the type of linkage formed between

the molecules.

(c) This polymer is not considered to be particularly hazardous to the environment.

Comment on possible reasons for this.

................................................................................................................

................................................................................................................(Total 5 marks)


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NT Exampro 4

5. Suggest why polymers such as Terylene soften over a range of temperatures rather than having asharp melting point.

......................................................................................................................

..................................................................................................................................(1)

6. The characteristic reactions of benzene can be classified as electrophilic substitution reactions.

(a) Select a reaction of benzene which illustrates this type of reaction. Give the reagents andthe equation for this reaction, the conditions under which it occurs and the name of the

organic product.

Reagent(s): ................................................................................................................

Equation: ...................................................................................................................

Conditions: .................................................................................................................

Name of organic product: ..........................................................................................(4)

(b) For the reaction selected in (a):

(i) identify the electrophile;

..........................................................................................................................(1)

(ii) give an equation to show its formation;

..........................................................................................................................(2)

(iii) give the mechanism for the substitution reaction.

(3)

(c) Give two specificsafety precautions you would need to take in carrying outthereaction in (a).

....................................................................................................................................

....................................................................................................................................(2)


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NT Exampro 5

(d) Give one reaction of the functional group which was introduced into the benzene ring as aresult of the reaction performed in (a). Give the reagents, conditions and equation for this

reaction.

Reagent: ....................................................................................................................

Conditions: ................................................................................................................

Equation: ...................................................................................................................(3)

(Total 15 marks)

7. When excess methane reacts with chlorine, the main product is chloromethane.

(i) Under what conditions does this reaction occur?

(1)

(ii) Give the mechanism for this reaction.

(4)

(Total 5 marks)

8. (a) Acyl halides such as ethanoyl chloride, CH3COCl, are useful synthetic intermediates

because they are quite reactive.

(i) Suggest synthetic steps, giving reagents and conditions, by means of which ethanolcould be converted to ethanoyl chloride.

...........................................................

...........................................................

...........................................................

...........................................................

...........................................................

...........................................................(5)


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NT Exampro 6

(ii) Ethanoyl chloride, CH3COCl, reacts violently with water at room temperature,

whereas chloroethane, CH3CH2Cl, reacts extremely slowly with water under the

same conditions. Suggest a reason why CH3COCI is moresusceptible to

nucleophilic attack than CH3CH2Cl.

...........................................................

...........................................................

...........................................................(2)

(b) Ethyl ethanoate CH3COOCH2CH3can be made either from ethanol and ethanoic acid or

from ethanol and ethanoyl chloride.

(i) Give the equations for the two reactions.

...........................................................

...........................................................(2)

(ii) Suggest why the reaction with ethanoyl chloride gives a better yield of the ester.

...........................................................

...........................................................(1)

(Total 10 marks)

9. (a) Ethane reacts with chlorine in the presence of ultraviolet light,

(i) What is the function of the u.v. light?

...........................................................(1)

(ii) The reaction gives more than one chlorine-containing organic product.

Explain why this is so.

...........................................................

...........................................................(1)


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NT Exampro 7

(iii) State the name of one other product formed in this reaction which does not containchlorine and account for its formation.

...........................................................

...........................................................

...........................................................

...........................................................(3)

(b) Methylbenzene reacts with chlorine in the presence of u.v. light in a similar way

to methane:

+ Cl + HCl2

3 2CH CH Cl

In order for the reaction to take place, chlorine must be passed into boiling methylbenzene

in the presence of u.v. light over a period of time.

(i) Draw an apparatus which could be used for this reaction

(3)

(ii) What are the hazards specificto this experiments

...........................................................

...........................................................(2)

(iii) Assuming that the organic product from this reaction consists only of

methylbenzene and (chloromethyl)benzene, and that Raoult's Law applies to the

mixture of the two liquids, sketch a boiling-point/composition diagram for the

mixture and use it to show how fractional distillation enables the components of the

mixture to be separated. Methylbenzene boils at 111oC, (chloromethyl)benzene at179C.


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NT Exampro 8

179 C

111 C

...........................................................

...........................................................

...........................................................(4)

(Total 14 marks)

10. Grignard reagents are useful in organic syntheses where it is necessary to form a new

carbon-carbon bond.

(a) Draw a diagram of suitable apparatus, state the conditions and ONE specific safety

precaution for the preparation of the Grignard reagent 1-propylmagnesium bromide,

CH3CH2CH2MgBr, from 1-bromopropane. The following data will be useful.

Substance Boiling temperature

/C

Flammability

1-bromopropane 70.8 low

ethoxyethane (ether) 34.5 very high

(7)

(b) Give the names and structural formulae of the organic products obtained when1-propylmagnesium bromide reacts with:

(i) ethanal, followed by dilute hydrochloric acid

(2)


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NT Exampro 9

(ii) carbon dioxide followed by dilute hydrochloric acid

(2)(Total 11 marks)

11. This question concerns the three isomers A, B and C, each of which has a relative molecular

mass of 134.

C C

O

H

O

CH

CH CH OH

CH CHCH

CH

2

2

2 23

A B

C

(a) The mass spectrum of substance A is shown below. Identify the species responsible for

the peaks labelled 1, 2 and 3.

Peak 1 .........................................................................................................................

Peak 2 .........................................................................................................................

Peak 3 .........................................................................................................................(3)

(b) The infra-red spectra of two of these substances were also measured.

(i) Use the table and the spectra below to identify which spectrum is that ofsubstance C.

BondWavenumber

/ cm1 BondWavenumber

/ cm1

CH (arenes) 3000-3100 OH (hydrogen bonded) 3200-3570

CH (alkanes) 2850-3000 OH (not hydrogen

bonded)

3580-3650

C==O 1680-1750 C==C (arenes) 1450-1600

The spectrum of substance C is spectrum number ..........................................

(1)


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NT Exampro 10

(ii) Give one reason for your choice.

......................................................................................................................(1)

(iii) Give one other reason why the other spectrum could notbe that of substance C.

......................................................................................................................

......................................................................................................................(1)

100

80

60

40

20

0

Relative

intensity

25 50 75 100 125m/e

1

2

3

100

50

0

4000 3000 2000 1500 1000Wavenumber/cm1

Transmittance


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NT Exampro 11

100

50

04000 3000 2000 1500 1000

Wavenumber/cm1

Transm

ittance

(c) State which of the substances A, B and C will react with the following reagents and state

what would be observed.

(i) Bromine dissolved in hexane.

Substance(s) .....................................................................................................

Observation ......................................................................................................(2)

(ii) A warm ammoniacal solution of silver nitrate.

Substance(s) .....................................................................................................

Observation ......................................................................................................

(2)

(iii) 2,4-dinitrophenylhydrazine solution.

Substance(s) .....................................................................................................

Observation ......................................................................................................(3)

(iv) Give the structural formula of the organic product(s) obtained in (c)(i).

(1)


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NT Exampro 12

(v) Give the structural formula of the organic product(s) obtained in (c)(ii).

(1)

(d) (i) Give the reagents and the conditions necessary for the preparation of A from

benzene.

Reagents .......................................................................................................

Conditions ....................................................................................................(3)

(ii) This is an electrophilic substitution reaction. Write an equation to show theformation of the electrophile.

......................................................................................................................(2)

(Total 20 marks)

12. (a) Three isomers A, Band Bhave the molecular formula C4H8O.

All three compounds give an orange precipitate with 2,4-dinitrophenylhydrazine reagent.Band Calso give a silver mirror when warmed with ammoniacal silver nitrate solution.

Write the structural formulae of A, Band C.

Substance A

Substance B


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NT Exampro 13

Substance C

(3)

(b) Substance Areacts with the Grignard reagent, C2H5MgBr

(i) Give the equation for the preparation of this Grignard reagent.

..(1)

(ii) State the conditions for this preparation.

..

..(2)

(iii) Write the structural formula of the product obtained when this Grignard reagentreacts with substance A.

(1)

(c) C2H5MgBr reacts with carbon dioxide to form the acid C2H5COOH. This acid can be

converted to propanamide in a two step process.

C2H5COOH

step 1

C2H5COCl

step 2

C2H5CONH2

State the reagentrequired for each step.

Step 1 .

Step 2 .(2)


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NT Exampro 14

(d) C2H5MgBr also reacts with ethanal to form substance D, which exists as a pair of optical

isomers.

(i) Draw the structural formulae of these two isomers and use them to explain whythese isomers exist.

(4)

(ii) What is the difference in property between these isomers?

..(1)

(e) (i) Write down the name and the structural formula of the organic compound formedwhen substance Dis heated under reflux with a solution of potassium

dichromate(VI) in dilute sulphuric acid.

Name ..

Structural formula.

(2)

(ii) State the colour of the solution remaining after this reaction.

..(1)

(Total 17 marks)

13. (a) (i) Give the structural formula of a nitrile, C4H7N, that has an unbranched chain.

(1)

(ii) Primary amines can be made by reducing nitriles. Suggest a reagent that could be

used for this purpose.


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NT Exampro 15

............................................................................................................................(1)

(iii) Draw the structural formula of the amine produced by reducing the nitrile given in

(a)(i).

(1)

(b) Draw the structure of an isomer of C4H11N which has a chiral centre in the molecule and

identify the chiral centre.

(2)

(c) (i) What feature of an amine molecule makes it both a base and a nucleophile?

............................................................................................................................(1)

(ii) Give, by writing an equation, an example of an amine acting as a base.

............................................................................................................................(1)

(d) Ethanoyl chloride, CH3COCl, reacts with both amines and alcohols.

(i) Give the name of the type of compound produced when ethanoyl chloride reactswith ethylamine, C2H5NH2.

............................................................................................................................(1)

(ii) State one of the advantages of reacting ethanoyl chloride with ethanol to make an

ester rather than reacting ethanoic acid with ethanol.

............................................................................................................................(1)

(e) Ethanoyl chloride can be made from ethanoic acid.

(i) Suggest a reagent suitable for this conversion.

............................................................................................................................


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NT Exampro 16

(1)

(ii) Suggest how chloromethane can be converted into ethanoic acid via a Grignard

reagent. (Details of the experimental apparatus are not required.)

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................(4)

(Total 14 marks)

14. (a) An alcohol with the molecular formula C4H9OH is chiral.

(i) Explain what is meant by the term chiral.

............................................................................................................................

............................................................................................................................(2)

(ii) Draw two diagrams to clearly represent the optical isomers that result from the

chirality of this alcohol.

(2)

(iii) Explain how you could distinguish between these two isomers experimentally.

............................................................................................................................

............................................................................................................................

............................................................................................................................(2)

(b) Alcohols react with carboxylic acids to form esters.

(i) Write an equation for a typical esterification reaction.

............................................................................................................................(1)


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NT Exampro 17

(ii) Suggest how this type of reaction could be used to form polyesters.

Experimental details are not required.

............................................................................................................................

............................................................................................................................

............................................................................................................................(3)

(iii) Suggest, with reasoning, whether a laboratory coat made from a polyester might bedamaged by a spillage on it of hot concentrated aqueous sodium hydroxide solution.

............................................................................................................................

............................................................................................................................

............................................................................................................................(2)

(iv) Give another typeof reagent that could be used to make an ester from an alcohol.

............................................................................................................................(1)

(Total 13 marks)

15. Consider the following reaction scheme starting from propanone.

H J K+ C O

CH

CH

3

3

33

3

2

2

2

33

3

propanoneReagent 1

Reagent 3

Reagent 2CH OH

CH COOH

CH Cl

CH C O

CH Cl

CH C O

CC

C

Cl

NH

Br

NaOH

HCN

NaCN

I

NaOH

M

(a) Give the structural formula of:

H


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NT Exampro 18

J

K

M

(4)

(b) Identify:

Reagent 1: ..................................................................................................................

Reagent 2: ..................................................................................................................

Reagent 3: ..................................................................................................................(3)

(c) Compounds produced when glucose C6H12O6, is metabolised include:

CH2(OH)CH(OH)CHO CH3COCOOH CH3CH(OH)COOH

2,3-dihydroxypropanal 2-oxopropanoic acid 2-hydroxypropanoic acid

(i) Draw the full structural formula for 2,3-dihydroxypropanal.

(1)


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NT Exampro 19

(ii) Suggest two of these compounds which would give a positive test with2,4-dinitrophenylhydrazine solution. State what you would see for a positive test

result.

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................(3)

(iii) Describe a test which would enable you to distinguish between the twocompounds

identified in part (ii).

............................................................................................................................

............................................................................................................................

............................................................................................................................

............................................................................................................................(2)

(Total 13 marks)

16. (a) Pure copper is needed for electrical applications. The purity of a sample of copper can be

found by reacting it with concentrated nitric acid, neutralising the resulting solution and

treating it with excess potassium iodide. Iodine is liberated and this can be titrated with

standard sodium thiosulphate solution. The reactions are:

Cu(s) + 4HNO3(l) Cu(NO3)2(aq) + 2NO2(g) + 2H2O(1)

2Cu2+(aq) + 4I(aq) 2CuI(s) + I2(aq)

A copper foil electrode from an electric cell weighs 1.74 g. It was made into 250 cm3of a

solution of copper(II) ions. To 25.0 cm3of this solution excess iodide ions were added,

and the mixture titrated with 0.100 mol dm3sodium thiosulphate solution. On average26.8 cm3was required. Calculate the percentage purity of the copper foil.

(6)

(b) Copper(II) chloride is used as a catalyst in the reaction of benzenediazonium chloride inthe presence of hydrochloric acid to givechlorobenzene:

C6H5N+

2 ClC6H5Cl + N2

The catalytic effect of transition metals or their ions is often attributed to their having

several stable oxidation states. Explain why such states are possible in transition metals

and why they are important in catalysis.(4)

(c) (i) State the reagents and conditions needed to make benzenediazonium chloride from

phenylamine.(2)

(ii) Explain why the temperature needs to be carefully controlled in the reaction in part(i).


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NT Exampro 20

(2)

(iii) Write the equation for the reaction of benzenediazonium chloride with phenol using

structural formulae. Give the conditions under which benzenediazonium chloride

reacts with phenol and state what you would see.(5)

(d) Phenylamine is prepared from benzene. Give the reagents and conditions needed for eachof the steps in the conversion of benzene to phenylamine.

(6)

(Total 25 marks)

17. (a) Write equations to show the reactions of the amino acid alanine, CH3CH(NH2)COOH,

with:

(i) HCl

....(1)

(ii) NaOH

....(1)

(b) Explain why alanine has a relatively high melting temperature (290 C).

......

......

......(2)

(c) Alanine exists as two optical isomers.

(i) Draw diagrams to show the structures of the two optical isomers.

(2)


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NT Exampro 21

(ii) Explain how separate pure samples of each optical isomer can be distinguishedfrom each other.

....

....

....(2)

(d) A mixture of isomeric alkenes is obtained when butan-2-ol is dehydrated.

(i) Draw diagrams to show the two structuralisomers obtained when butan-2-ol

is dehydrated.

(2)

(ii) One of the above structural isomers can itself exist as two different stereoisomers.

Draw diagrams to clearly illustrate these two stereoisomers, and name this type of

stereoisomerism.

Type of stereoisomerism ..

Diagrams

(3)(Total 13 marks)

18. (a) Write the structural formulae of the organic products obtained when ethanoyl chloride

reacts with the following compounds. Give the names of these products.

(i) Ammonia, NH3.

Structure

Name (2)(ii) Methanol, CH3OH.


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NT Exampro 22

Structure

Name (2)

(b) Bromoethane reacts with magnesium to form the Grignard reagent CH3CH2MgBr.

This Grignard reagent reacts with:

CO2, followed by hydrochloric acid, to form compound A; water to form compound B; methanal, followed by hydrochloric acid, to form compound C.Compounds Aand Creact together, in the presence of a suitable catalyst, to

form compound D.

(i) Write the structural formulae of compounds A, B, and C.

A B

C

(3)

(ii) Draw the full structural formula of compound D.

(2)


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NT Exampro 23

(iii) Give the names of compounds Cand D.

Name of C.

Name of D.(2)

(iv) Identify a catalyst for the reaction between compounds Aand C.

(1)

(Total 12 marks)

19. (a) An alcohol, C3H8O, was analysed by low resolution NMR spectroscopy. The spectrum is

given below.

7 6 5 4 3 2 1 0

ppm

The chemical shifts of some hydrogen nuclei are given in the following table (where Rrepresents an alkyl group).

group / ppm group / ppm

CH3R 0.81.2 ROH 1.06.0

RCH2R 1.11.5 RCH2OH 3.34.0

CHR3 1.5 R2CHOH 3.24.1

Show that the alcohol must be propan-2-ol.(2)

(b) By considering the shapes of the molecules of CH4and H2O explain why a molecule of

propan-2-ol has bond angles of approximately 109 except in the bond COH where theangle is approximately 107.

(4)


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NT Exampro 24

(c) Propan-2-ol can be oxidised by an aqueous solution of potassium dichromate(VI)acidified with dilute sulphuric acid. The two half-equations for the reactions involved are:

Cr2O72(aq) + 14H+(aq) + 6e 2Cr3+(aq) + 7H2O(l)

C3H6O(aq) + 2H+(aq) + 2e C3H7OH(aq)

(i) Oxidation of the alcohol takes place. Explain what this indicates about the standardelectrode potentials of the two half reactions. Write the equation for the reaction.

(3)

(ii) An aqueous solution of chromium(III) ions is coloured. Explain the cause of this

colour.(3)

(iii) What would you see if the organic product of the oxidation reaction reacts with

iodine in alkaline solution? Write the equation for the reaction.(3)

(d) (i) State the name of the organic product if propan-2-ol is heated with concentratedsulphuric acid and classify the type of reaction occuring.

(2)

(ii) Draw the structural formula of the organic product that results from heating

propan-2-ol with a mixture of sodium bromide and 50% sulphuric acid.(1)

(Total 18 marks)

20. A compound D, CH3.CH(OH).COOH, may be prepared from C3H7OH by the following series

of reactions.

C H OH C H O

C H O Cl

3 3

3

7 6

5

2

2 2 7 2 4

2

2

A

D

B

C

K Cr O (aq)/H SO (aq)

Cl (g)/uv light

(i) NaOH(aq)

(ii) HCl(aq)

(a) (i) Identify compounds A, Band C.(3)

(ii) Classify the reaction with chlorine.(2)


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(iii) Dhas a boiling temperature of 186C whereas C, C3H5O2Cl, boils at 122C. Draw

a boiling temperature/composition diagram applicable to a mixture of Cand Dand

use it to show how fractional distillation of a mixture of the two compounds couldproduce a sample of D.

(5)

(b) Assuming the percentage yield for each step in sequence to be 80%, calculate the mass of

Dthat could be made from 60 g of C3H7OH.(3)

(c) An aqueous solution of Dof concentration 0.100 mol dm3has a pH value of 2.04.

(i) Calculate the value of the dissociation constant, Ka, for D.

(3)

(ii) Suggest, with reasoning, whether Dor propanoic acid, CH3CH2COOH,

Ka= 1.3 105mol dm3, would be more exothermic in reaction with aqueous

sodium hydroxide solution of concentration 0.1 mol dm3.(2)

(Total 18 marks)

Chemistry Exercise

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