Chem ch10

Worked solutions to student book questions Chapter 10 Organic reactions: pathways to new products

Heinemann Chemistry 2 4th edition Enhanced Copyright Pearson Australia 2010 (a division of Pearson Australia Group Pty Ltd) 1

Q1. Write balanced equations to represent the formation of all possible products of the reactions of chlorine with methane.

A1.

CH4(g) + Cl2(g) CH3Cl(g) + HCl(g) CH3Cl(g) + Cl2(g) CH2Cl2(g) + HCl(g) CH2Cl2(g) + Cl2(g) CHCl3(g) + HCl(g) CHCl3(g) + Cl2(g) CCl4(g) + HCl(g)

Q2. Draw the structural formulas and name all the possible products that can be formed by the reaction of chlorine with ethane. Which substances are isomers?

A2.

chloroethane: 1,1-dichloroethane; 1,2-dichloroethane; 1,1,1-trichloroethane 1,1,2-trichloroethane: 1,1,1,2-tetrachloroethane; 1,1,2,2-tetrachloroethane 1,1,1,2,2-pentachloroethane: hexachloroethane Isomers are 1,1-dichloroethane and 1,2-dichloroethane 1,1,1-trichloroethane and 1,1,2-trichloroethane 1,1,1,2-tetrachloroethane and 1,1,2,2-tetrachloroethane



Q3. Name the products formed when ethene reacts with: a hydrogen chloride b chlorine c water d hydrogen

A3. a chloroethane b 1,2-dichloroethane c ethanol d ethane

Q4. Use structural formulas to write equations and name the products for the reactions of: a but-1-ene with chlorine b but-2-ene with hydrogen bromide

A4.

a

b



Q5. Polyethenol is used to make soluble hospital laundry bags. The structure of the monomer ethenol is shown in Figure 10.9. Draw the structure of a section of the polymer.

Figure 10.9 Structure of ethenol.

A5.

Q6. Draw molecular structures and refer to the electronegativities given in the periodic table at the end of this book to work out whether each of the following substances has a dipole or is non-polar. a CH3F b CH3CCl3 c CCl3CH2CCl3

A6. a polar b polar c non-polar

Q7. Write unbalanced equations for the production of: a methanol from chloromethane b chloromethane from methane c propan-1-ol from 1-chloropropane

A7.

a CH3Cl(g) OH

CH3OH(aq) b CH4(g) 2Cl UV light CH3Cl(g)

c CH3CH2CH2Cl(l) OH

CH3CH2CH2OH(l)



Q8. Write a sequence of reactions that shows the production of: a ethanoic acid from ethane b ethanoic acid from ethene.

A8.

a CH3CH3(g) 2Clheat or UV light CH3CH2Cl(g) OH CH3CH2OH(aq)

22 7Cr OH

+ CH3COOH(aq)

b CH2CH2(g) 23 4

H OH PO catalyst CH3CH2OH(g)

22 7Cr OH

+ CH3COOH(aq)

Q9. Label each step in Question 8 to show whether it is an addition, substitution or oxidation reaction.

A9. a substitution, substitution, oxidation b addition, oxidation

Q10. Write balanced equations for the reaction between ethanoic acid and: a sodium hydroxide solution b magnesium metal c sodium carbonate solution.

A10.

a CH3COOH(aq) + NaOH(aq) CH3COONa(aq) + H2O(l) b 2CH3COOH(aq) + Mg(s) (CH3COO)2Mg(aq) + H2O(l) c 2CH3COOH(aq) + Na2CO3(aq) 2CH3COONa(aq) + CO2(g) + H2O(l)



E1. A condensation polymer used in medical sutures is made from glycolic acid monomer. The semi-structural formula of glycolic acid is HOCH2COOH. a What is meant by the term condensation polymer? b Name the functional groups present in glycolic acid. c Write an equation to represent the formation of a section of the polymer. d Draw the structural formula for a section of the polymer and circle the ester bond.

AE1. a When condensation polymers are formed, small molecules such as water are

eliminated when the monomer molecules combine. b hydroxyl,OH and carboxyl, COOH functional groups c, d

Q11. Draw the structural formulas of the following esters and name them. a CH3COOCH3 b CH3COOCH2CH3 c CH3CH2COOCH2CH3

A11.

a

b



c

Q12. Write equations that describe the formation of an ester that smells like: a pineapple (ethyl butanoate) b rum (ethyl methanoate).

A12.

a CH3CH2CH2COOH(l) + CH3CH2OH(l) 42SOH CH3CH2CH2COOCH2CH3(l) + H2O(l)

b HCOOH(l) + CH3CH2OH(l) 42SOH HCOOCH2CH3(l) + H2O(l)

Q13. Devise reaction pathways for the following reactions: a ethylamine from ethene b butan-1-ol from butane c pentanoic acid from 1-chloropentane

A13.

a Ethene 2H O ethanol 3NH ethylamine

b Butane 2Cl 1-chlorobutane OH butan-1-ol

c 1-Chloropentane OH 1-pentanol 22 7Cr O ,H + pentanoic acid

Q14. Name these esters and provide the systematic name of the alkanols and carboxylic acids used to form them. a CH3CH2CH2CH2COOCH3 b CH3CH2COOCH2CH2CH2CH2CH2CH3

A14.

a methyl pentanoate, from methanol and pentanoic acid b hexyl propanoate, from hexanol and propanoic acid

Q15. Propose the shortest reaction pathway that will synthesise the following: a methanoic acid from methane b ethanol from ethene c propyl methanoate from propane and methane



A15.

a methane 2Cl ,UV light chloromethane OH methanol 22 7Cr O ,H + methanoic acid

b ethene 2H O ethanol c This synthesis can be carried out in three stages: (i) synthesis of propan-1-ol,

(ii) synthesis of methanoic acid and (iii) synthesis of 1-propyl methanoate i propene 2Cl 1-chloropropane OH propan-1-ol and

ii methane 2Cl chloromethane OH methanol 22 7Cr O ,H + methanoic acid then

iii propan-1-ol + methanoic acid H+ 1-propyl methanoate + water

Q16. Describe a reaction pathway to synthesise 1-butyl ethanoate using the appropriate alkanes or alkenes as starting materials.

A16. This synthesis is carried out in three parts: (i). synthesis of 1-butanol, (ii) synthesis of ethanoic acid and (iii) synthesis of 1-butyl ethanoate. i butane 2Cl 1-chlorobutane OH butan-1-ol

ii ethene 2H O ethanol 22 7Cr O ,H + ethanoic acid iii ethanoic acid + butan-1-ol 1-butyl ethanoate + water

Q17. Calculate the percentage yield if 5.0 g of ethanol is oxidised to produce 4.8 g of ethanoic acid.

A17.

CH3CH2OH 2

2 7Cr O ,H +

CH3COOH Theoretical yield (100% conversion of ethanol)

n(CH3COOH) = n(CH3CH2OH)

= 465 mol

m(CH3COOH) = 465 60 g = 5.2 g

% yield = product mass ltheoretica

obtainedproduct mass actual 100%

= 2.58.4 100

= 92%



Q18. Compound D can be synthesised using a reaction pathway that involves a number of intermediate steps. The yield for each step is shown.

A %70 B

%50 C

%90 D

a Determine the overall yield for the preparation of compound D from compound A.

b How would the overall yield be affected if the yield for B C was only 10%?

A18. a yield = 0.7 0.5 0.9 = 0.32; Yield = 32% b yield = 0.7 0.1 0.9 = 0.063; Yield = 6.3%

Q19. Briefly describe the principles of fractional distillation.

A19. In fractional distillation, the components of a mixture of volatile liquids are separated by what can be considered to be a succession of simple distillations. The temperature gradient in the fractionating column allows this to occur. Fractional distillation relies on the phenomena that the concentration of the low boiling point component in the vapour over a mixture of volatile liquids is higher than in the liquid. As the mixture of liquids is heated in the distillation flask, the vapours that move up the fractionating column contain a higher concentration of the more volatile liquid. The vapours eventually reach a height in the fractionating column where the temperature is low enough for condensation to occur. As the condensed liquid moves back down the column it is reheated by vapours rising from the distillation flask. Some of this condensed liquid evaporates and the resulting vapour has an even higher concentration of the low boiling point substance. This process of evaporation and condensation is repeated many times. The concentration of the more volatile substance increases in each evaporationcondensation cycle. Once the vapour reaches the top of the fractionating column it will ideally consist of only the more volatile component. When the relatively pure component reaches the top of the fractionating column, the temperature remains relatively stable. The material that condenses over a small temperature range near the boiling point is collected once it has passed through the condenser.

Q20. Methane undergoes a series substitution reactions with bromine to form a number of compounds with the following boiling points: bromomethane (3.6C), dibromomethane (97C), tribromomethane (150C) and tetrabromomethane (190C). Describe how you would obtain pure samples of each compound from the mixture.



A20. The mixture of volatile liquids can be separated by fractional distillation. The mixture is placed in the distillation flask and heated. The most volatile compound (bromomethane) is the first to reach the top of the fractionating column and condense. The fraction condensing in a narrow range of temperatures around the boiling point 3.6C is collected. Because this temperature is below that of room temperature, the receiving flask should be surrounded by ice to condense the liquid bromomethane. The next fraction to be collected at around 97C will contain dibromomethane. Tribromomethane will be found in the fraction collected at 150C. Tetrabromomethane will found in the fraction collected at 190C.

Chapter review

Q21. Write unbalanced equations for the production of: a chloroethane from ethane b ethanol from ethene c ethanol from chloroethane d ethanoic acid from ethanol.

A21.

a CH3CH3(g) 2Cl ,UV light CH3CH2Cl(g) b CH2CH2(g) 2

3 4

H OH PO catalyst CH3CH2OH(g)

c CH3CH2Cl(g) OH

CH3CH2OH(aq)

d CH3CH2OH(aq) 2

2 7Cr O ,H +

CH3COOH(aq)

Q22.

Classify the reactions in your answers to Question 21 as addition or substitution.

A22. a substitution b addition c substitution d oxidation

Q23. Write the structural formulas of the products of the following reactions: a



b

c

d

A23.

a

b

c

d



Q24. Write an unbalanced chemical equation for the reaction between: a butane and chlorine b 1-chlorobutane and sodium hydroxide solution c butan-1-ol and acidified potassium dichromate solution d propan-1-ol and acidified potassium permanganate solution e ethane and oxygen.

A24.

a CH3CH2CH2CH3(g) 2Cl ,UV light CH3CH2CH2CH2Cl(l)

b CH3CH2CH2CH2Cl(l) OH

CH3CH2CH2CH2OH(aq)

c CH3CH2CH2CH2OH(aq) 2

2 7Cr O ,H +

CH3CH2CH2COOH(aq)

d CH3CH2CH2OH(aq) 4MnO ,H +

CH3CH2COOH(aq) e 2C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(g)

Q25. Write chemical equations in the form of a flow diagram (similar to Figure 10.31) to describe the preparation of propanoic acid from an: a alkane b alkene.

A25.

a

b



Q26. Consider the following compounds: I

II

III

IV

V

a Write the names of each of these compounds. b Which of these compounds is a member of the alkane homologous series? c Give one important difference in chemical behaviour between compounds I

and V. d What important chemical is manufactured from compound II? e Which of these compounds dissolves in water to form an acidic solution?



A26. a I methane, II chloroethane, III propane, IV ethanoic acid, V propene b I, III c Compound V will decolourise bromine almost immediately, whereas compound I

will not. In general, compound I participates in substitution reactions (e.g. chlorination by chlorine gas to form chloromethane) whereas compound V participates in addition reactions (e.g. addition of HCl across the double bond to form chloropropane).

d ethanol e IV

Q27. Complete the following reactions: a

b

c

A27. a CH3CH2COOCH3(l) + H2O(l) b CH3COO(CH2)4CH3(l) + H2O(l) c HCOOCH(CH3)2(l) + H2O(l)

Q28.

a Write a chemical equation to describe the preparation of propyl ethanoate from an alkanol and a carboxylic acid.

b What name is given to this type of reaction? c Sulfuric acid would be present in the reaction mixture. Why?

A28.

a CH3COOH(l) + CH3(CH2)2OH(l) 42SOH CH3COO(CH2)2CH3(l) + H2O(l) b condensation and esterification c catalyst



Q29. Write equations to show the production of: a methyl ethanoate b ethyl propanoate.

A29.

a CH3COOH(l) + CH3OH(l) 42SOH CH3COOCH3(l) + H2O(l) b CH3CH2COOH(l) + CH3CH2OH(l) 42SOH CH3CH2COOCH2CH3(l) +

H2O(l)

Q30. Write the formula of the alkanol and carboxylic acid used to make the following esters: a CH3COOCH2CH3 b CH3CH2COOCH2CH3

A30. a CH3CH2OH, CH3COOH b CH3CH2OH, CH3CH2COOH

Q31. In an experiment, the reaction of chlorine with ethane resulted in a mixture containing a number of products with the following boiling points: chloroethane (12C), 1,1-dichloroethane (57C), 1,2-dichloroethane (84C), and 1,1,2-trichloroethane (97C). Describe how you could obtain a pure sample of 1,2-dichloroethane from this mixture.

A31.

The mixture of volatile liquids can be separated by fractional distillation. The mixture is placed in the distillation flask and heated. The components in the mixture are separated in order of their boiling points with the most volatile component, chloroethane, being the first fraction to condense. This is followed by the fraction containing1,1-dichloroethane. The fraction condensing in a narrow range of temperatures around the boiling point of 1,2-dichlorethane, 84C, is then collected in a new receiving flask.

Q32. Complete the missing structural formulas and name the compounds A, B and C.



A32.

A

B NaOH(aq) C

Q33. Give the semi-structural formulas for substances P and Q and the systematic names for substances R and S in the following equation:

A33. Formula P: CH3OH Formula Q: H2O Substance R: propanoic acid Substance S: methyl propanoate

Q34. Write a reaction pathway for the synthesis of: a ethyl propanoate from ethene and propene b ethyl ethanoate from an alkene.

A34. a Preparation of ethanol

ethene 2H O(g) ethanol

Synthesis of propanoic acid propene 2H (g) propane 2Cl , UV light 1-chloropropane OH propan-1-ol

22 7Cr O ,H

+

propanoic acid Preparation of ethyl propanoate ethanol + propanoic acid ethyl propanol + water

b Preparation of ethanol ethene 2H O(g) ethanol

Preparation of ethanoic acid ethene 2H O(g) ethanol 22 7Cr O ,H + ethanoic acid ethanol + ethanoic acid ethyl ethanoate + water



Q35. Fractional distillation is an important laboratory technique. a What is fractional distillation used for? b Fractional distillation has been described as a series of simple distillations.

Explain.

A35. a Fractional distillation is used to separate liquids that have different boiling points.

It is commonly used in the laboratory to separate volatile liquids from a reaction mixture. Industrial applications of fractional distillation include: Separation of the fractions from crude oil. Production of oxygen and nitrogen by the fractional distillation of liquid air. Extraction of ethanol from water in the fermentation of sugar.

b The mixture of liquids is heated in the distillation flask. The vapours that move up the fractionating column contain a higher concentration of the more volatile liquid. The vapours eventually reach a height in the fractionating column where the temperature is low enough for condensation to occur. As the condensed liquid moves back down the column it is reheated by vapours rising from the distillation flask. Some of this condensed liquid evaporates and the resulting vapour has an even higher concentration of the low boiling point substance. This process of evaporation and condensation is repeated many times. The concentration of the more volatile substance increases in each evaporationcondensation cycle. At the same time the concentration of the less volatile (higher boiling point) substance in the distillation flask will increase. Once the vapour reaches the top of the fractionating column it will ideally consist of only the most volatile component.

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