HOMEWORK GUIDE

CHAPTER 22: Alkanols

Summary

A homologous series

The alkanols are a homologous series with the general formula CnH2n+1OH. The names

always end in -ol. All have the hydroxyl group –OH, which gives the alkanols similar

chemical properties.

Note: The hydroxyl group --OH is covalent, and differs from OH-, which is the hydroxide

ion.

The first two alkanols are methanol CH3OH and ethanol C2H5OH or CH3CH2OH. Structural formulae of ethanol

Ethanol is the most important alcohol.

Preparation of ethanol

By fermentation of sugars found in plants, e.g. grapes, barley, rice. Fermentation is the

conversion of large molecules (e.g.. starch, sugars) to smaller molecules (e.g., ethanol) by

micro-organisms (e.g. yeast). For example, the fermentation of a sugar (glucose):

C6H12O6(aq) -------------------> 2C2H5OH(aq) + 2CO2(g)

glucose ethanol carbon dioxide

The process works best at about 37OC; higher temperatures kill the yeast. The maximum

concentration of ethanol is about 18%. This is because the yeast dies at higher

concentration and fermentation stops. The concentration can be increased by fractional

distillation.

By the catalytic hydration of ethene

Ethanol and steam are passed over a catalyst of phosphoric acid at 300OC and high

pressure.

C2H4(g) + H2O(g) ------------------------> C2H5OH(g)

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phosphoric acid300OC

enzymes in yeast

Uses of lower alkanols

As solvents: E.g. In perfumes and cosmetics to dissolve fragrant oils.

Methylated spirit is a mixture of methanol and ethanol.

As fuels: E.g. Ethanol in spirit burners, as a fuel for cars in some countries (e.g. Brazil).

In other places, gasohol (ethanol mixed with petrol) is used.

In alcoholic drinks: E.g. Ethanol in beers (from barley / prepared by fermentation), wines

(from grapes or rice / prepared by fermentation), brandy (from grapes / prepared by

fermentation plus distillation).

Production of vinegar from ethanol. (See below.)

Production of esters: (See below.)

Properties and reactions of alkanols

Solubility: Lower alkanols (C1 – C3) are soluble in water (due to the hydroxyl group) and

in non-aqueous solvents (due to the hydrocarbon part of the molecule). Hence the are

used for mixing oils and water in cosmetics.

Burning: Alkanols burns completely with hot clean blue flames. E.g. ethanol:

C2H5OH(l) + 3O2(g) ----> 2CO2(g) + 3H2O(l)

Oxidation: Alkanols can be oxidised to alkanoic acids with potassium dichromate

solution acidified with dilute sulphuric acid. For example, oxidation of ethanol:

CH3CH2OH(l) + 2[O] ----> CH3COOH(aq) + H2O(l)

from the oxidising agent ethanoic acid

Esterification: This is the reaction of an alkanol with an alkanoic acid to form an ester

and water. For example:

CH3COOH + CH3CH2OH -----> CH3COOCH2CH3 + H2O

ethanoic acid + ethanol ------> ethyl ethanoate + water

The lower esters are liquids with a sweet fruity smell. They are used as artificial flavours,

as fragrances for perfumes and cosmetics, and as solvents e.g. in nail polish remover and

some glues.

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Organic acids

Organic acids are a homologous series with the general formula CnH2n+1COOH. All have

the -COOH group. The most common example is ethanoic acid CH3COOH.

Structural formula of ethanoic acid

Vinegar is a dilute solution of ethanoic acid. It is prepared industrially by adding suitable

micro-organisms to ethanol and exposing the mixture to air for 1 or 2 weeks.

Ethanoic acid is a weak acid. It reacts slowly with some metals to give hydrogen, and

with carbonates to give carbon dioxide.

Problems associated with drinking alcohol

Drinking even small amounts of alcohol can affect a person’s behaviour. For example, a

person is unable to see or speak clearly and unable to stand or walk properly.

Continual drinking over a long period (e.g. several years) can cause health problems.

For example:

-- damage to the brain, liver and stomach.

-- some cancers, e.g. mouth, throat and gullet.

-- high blood pressure.

-- alcohol can pass from a mother to her unborn child and harm the baby.

There are social and economic problems associated with alcohol. For example:

-- alcohol addiction.

-- family and work problems.

-- alcohol is a major cause of road accidents.

-- economic costs include hospital costs, legal costs and costs from lost work.

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22.1 – 22.4

Multiple-choice questions

1. The chemical name for the substance ‘alcohol’ is

A ethane

B ethene

C ethanol D ethanoic acid.

2. Which of the following are uses of ethanol?

(1) In alcoholic drinks.

(2) As a solvent for perfumes and cosmetics.

(3) As an alternative fuel for motor cars.

A (1) only

B (1) and (2) only

C (2) and (3) only

D (1), (2) and (3)

3. Which of the following are examples of alcoholic drinks?

(1) Coca cola.

(2) Beer

(3) Wine

A (1) only

B (2) only

C (2) and (3) only D (1), (2) and (3)

4. What is the general formula for the alkanols?

A CnH2n+2

B CnH2n+1OH C CnH2n+2OH

D CnH2n+1COOH

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5. The diagram shows a ball-and-stick model of an alkanol. What is its name?

A Methanol.

B Ethanol. C Propanol.

D Butanol.

6. What is the systematic name of the alkanol with the following structural formula?

CH3 – CH2 – CH2 – CH2 – OH

A butanol.

B butanol-1.

C butan-1-ol. D butan-4-ol.

7. What compound is reacted with steam in the manufacture of ethanol?

A Ethene. B Ethane.

C Ethanoic acid.

D Glucose.

Questions 8 to 10 relate to the following alcoholic drinks:

A Beer.

B Wine.

C Brandy.

D Whisky.

8. Which drink is made by fermentation using grapes? B

9. Which drink is made by the fermentation of grapes followed by distillation of the

fermentation mixture? C

10. Which drink contains the lowest concentration of alcohol? A

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11. In the fermentation of a sugar, what are the final products?

A Water and carbon dioxide.

B Ethanol only.

C Ethanol and water.

D Ethanol and carbon dioxide.

12. Methylated spirit is an industrial solvent and fuel. What does it consist of?

A Methanol.

B Ethanol.

C Methanol and ethanol. D Methanoic acid.

13. Some micro-organisms are added to a dilute solution of ethanol. The mixture is exposed

to the air for a few weeks. What is produced?

A Ethane.

B Ethane.

C An ester.

D Vinegar.

14. Which of the following statements about esters is INCORRECT?

A They are found naturally in many fruits.

B They can be made from alkanols.

C Synthetic esters are added to foods and drinks as flavourings.

D They can be used as fuels instead of petrol.

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Structured questions

1. The alkanols are a homologous series.

(a) (i) What is another name for the alkanols? __The alcohols.__________________

(ii) What is their general formula? _____CnH2n+1OH.______________________

(b) Name the first two alkanols and write the condensed structural formulae for each.

___1. Methanol, CH3OH. 2. Ethanol, CH3CH2OH._________________________

(c) What is common about the names of the alkanols?

__They all end in – ol. __________________________________________________

(d) What functional group do all alkanols have?

__The hydroxyl group, -OH.___________________________________________

(e) The third alkanol, C3H7OH exists as two isomers.

(i) What are isomers?

___Compounds with the same molecular formula but different structural formulae._

(ii) Write the name and structural formula for each of these isomers.

1.

2.

2. Ethanol can be manufactured from ethene.

(a) What other reactant is used? ____Steam._____________________________

(b) Write the equation for the reaction.

___C2H4(g) + H2O(g) -----> C2H5OH(g)______________________________

(c) What are the conditions for the reaction?

__High temperature (~300 O C), high pressure, and a catalyst (phosphoric acid). _____

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3. Ethanol (alcohol) can also be prepared from the starch and sugars in plants. This method is

used to prepare alcoholic drinks.

(a) What is the process called?

___Fermentation.________________________________________________________

(b) Name TWO plants used for this process and the kind of alcoholic drink prepared from

each.

___E.g. 1. Grapes to make wine.____________________________________________

_______2. Barley to make beer._____________________________________________

(c) To prepare ethanol, a solution of glucose (a sugar) is mixed with some yeast.

(i) What is the purpose of the yeast?

___The yeast contains an enzyme which speeds up the process of the

fermentation._______________________________________________________

(ii) Write the equation for the formation of the ethanol.

___C6H12O6(aq) ----> 2C2H5OH(aq) + 2CO2(g)______________________________

(iii) Only a dilute solution of ethanol can be formed. What is the reason for this?

___At higher concentrations, the yeast dies and the fermentation stops.______________

_______________________________________________________________________

(iv) What can be done to increase the concentration of the ethanol?

___The fermentation mixture can be distilled to increase the concentration of the ethanol._

4. Some uses of alkanols.

(a) Alkanols can be used as solvents. State some uses of ethanol as a solvent.

___It is used as a solvent for perfumes, cosmetics, paints and dyes.___________________

(b) Briefly describe how vinegar is prepared from ethanol.

__Some suitable micro-organisms are added to a dilute solution of ethanol. The mixture is

exposed to the air for a few weeks. The ethanol is converted into ethanoic acid /

vinegar._______________________________________________________________

(c) In some countries, ethanol is used as a fuel instead of petrol.

(i) Name one such country. __Brazil.________________________________

(ii) State an advantage of ethanol over petrol.

__Ethanol burns more cleanly / causes less air pollution than petrol._________________

(iii) How is the ethanol produced?

__By the fermentation of sugar from sugar cane._________________________________

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5. Esters are naturally-occurring compounds and can also be made synthetically.

(a) State a property of esters that makes them important compounds.

__They have a strong, pleasant/sweet smell. _________________________________

(b) State where esters occur naturally.

__In many fruits and flowers.___________________________________________

(c) State THREE uses of synthetic esters.

__E.g. As solvents (e.g. nail polish remover), as flavouring for foods and rinks (e.g. jellies,

milk shakes), and to provide fragrance/ a sweet smell in perfumes. _____________

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22.5 – 22.6

Multiple-choice questions

1. Which of the following statements about the properties of alkanols is INCORRECT?

A The chemical properties of all alkanols are similar.

B The chemical properties of alkanols are due to the hydroxyl group, -OH.

C The lower alkanols are insoluble in water but soluble in non-aqueous solvents. D As the hydrocarbon part of the alkanol molecule increases, there is a gradual change in

physical properties.

2. Ethanol has the formula C2H5OH. Which of the following statements concerning this

formula is/are correct?

(1) The –OH part is responsible for all the properties of ethanol.

(2) The –OH part is soluble in water but not in oils.

(3) The C2H5- part is soluble in non-aqueous solvents such as oils.

A (1) only

B (1) and (2) only

C (2) and (3) only D (1), (2) and (3)

3. Which of the following statements about the combustion of alkanols is/are correct?

(1) They burn with a clean flame.

(2) The combustion is a redox reaction.

(3) Carbon dioxide and water are always formed.

A (1) only

B (1) and (3) only

C (2) and (3) only

D (1), (2) and (3)

Questions 4 and 5 refer to the following types of reactions:

A Displacement.

B Redox.

C Esterification.

D Neutralisation

4. Some ethanol is added to acidified potassium dichromate solution. What type of reaction

occurs? B

5. What is the type of reaction between an alkanol and an alkanoic acid called? C

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Questions 6 and 7 refer to the ester formed when methanol and ethanoic acid react.

6. What is the name of the ester?

A Methyl methanoate.

B Methyl ethanoate. C Ethyl methanoate.

D Ethyl ethanoate.

7. What is the formula of the ester?

A CH3COOCH3 B CH3COOCH2CH3

C CH3CH2COOCH3

D CH3CH2OOCH2CH3

8. Which of the following is NOT a homologous series?

A Alkanes.

B Alkanols.

C Alkanoic acids.

D Esters.

9. What substance is represented by the model in the diagram

A Ethanol.

B Ethanoic acid. C Methanoic acid.

D Ethyl ethanoate.

10. What is the name of the compound with the formula HCOOH?

A Methanol.

B Methanoic acid. C Ethanoic acid.

D Methyl methanoate.

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Structured questions

1. Alkanol molecules are made up of two parts.

(a) Name the two parts.

__1. The hydroxyl group, -OH. ____________________________________________

__2. A hydrocarbon part. / (Alkyl group.)____________________________________

(b) Identify the two parts in a molecule of ethanol, C2H5OH.

__C2H5- (the hydrocarbon part) and – OH (the hydroxyl group). ___________________

(c) Which part is soluble in (i) water and (ii) oils?

__(i) The hydroxyl group. (ii) The hydrocarbon part._________________________

(d) Which part is mainly responsible for the chemical properties of an alkanol?

__The hydroxyl group._________________________________________________

2. The picture shows after-shave lotion. The lotion is a clear solution of water, oils and ethanol.

(a) Why are oils used in the after-shave lotion?

__To give the lotion a fragrance / pleasant smell._______________________________

(b) Why is ethanol included in the mixture?

__The ethanol dissolves both the water and the oils to give a clear mixture. Without the

ethanol, the oils would not mix with the water. ______________________________

_______________________________________________________________________

3. (a) What is an ester?

___A compound formed when an alkanol reacts with an alkanoic acid.___________

(b) Write the word equation for the formation of an ester.

__alkanoic acid + alkanol ---> ester + water_______________________________

(c) Do esters form a homologous series? ___No._____________________________

(d) State TWO properties of esters.

_1. They are liquids (at room temperature). __________________________________

__2. They have a sweet/pleasant smell. __________________________________

(e) Some esters occur naturally. Give TWO examples of where they are found.

__They occur in many fruits and flowers._________________________________

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(f) Some esters are made synthetically. Give some uses of these esters.

_E.g. 1. As flavourings in some foods and drinks. 2. To provide fragrance in perfumes and

other cosmetics. 3. Some are used as solvents, e.g. as nail polish remover.__________

_______________________________________________________________________

4. One ester is ethyl ethanoate.

(a) What alkanol is used to form this ester? __Ethanol.__________________________

(b) What alkanoic acid is used? __Ethanoic acid.____________________________

(c) Write the formula for the ester.

____CH3COOCH2CH3 ______________________________________________

(d) Write the chemical equation for the formation of this ester.

__ CH3COOH + CH3CH2OH -----> CH3COOCH2CH3 + H2O _____________

(e) There are many other esters.

(i) Write the name and formula for any ONE other ester.

__E.g. Methyl propanoate. CH3CH2COOCH3 ______________________________

(ii) Write the names and formulae of the alkanol and the alkanoic acid from which it is

formed.

__Methanol, CH3OH and propanoic acid, CH3CH2COOH_____________________

5. Write chemical equations for each of the following reactions:

(a) The combustion of (i) ethanol and (ii) methanol in air.

___(i) C 2H5OH(l) + 3O2(g) ----> 2CO2(g) + 3H2O(l)________________________

___(ii) 2 CH 3OH(l) + 3 O 2(g) ----> 2 CO 2(g) + 4H2O(l) ________________________

(b) Magnesium and ethanoic acid.

__2CH3COOH(aq) + Mg(s) ---> Mg(CH3COO)2(aq) + H2(g)_________________

(c) The formation of the ester you named in part (e) on Question 5.

__ CH3C H 2C OOH + CH 3OH -----> CH3C H 2C OOCH 3 + H2O ________________

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22.7

Multiple-choice questions

1. Which part of the body removes alcohol?

A Brain.

B Stomach.

C Liver. D Muscles.

2. Approximately what volume of alcohol can the body remove per hour?

A 0.1 cm3

B 1.0 cm3

C 10 cm3 D 100 cm3

Questions 3 and 4 relate to a person who drinks 3 cans of beer at a meal.

3. Approximately what volume of alcohol does the person consume?

A 3 cm3

B 30 cm3 C 60 cm3

D 600 cm3

4. How might this amount of alcohol affect the person? The person:

(1) has a relaxed feeling.

(2) become dizzy and cannot stand.

(3) is less alert.

A (1) only

B (2) only

C (1) and (3) only D (2) and (3) only

Questions 5 and 6 relate to the blood alcohol level (measured in mg per 100 cm3 of blood).

5. For driving in Hong Kong, what is the legal limit of the blood alcohol limit?

A 10

B 20

C 50 D 80

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6. This level can be reached by consuming how much alcoholic drink within an hour?

(1) 2 to 3 cans of beer.

(2) About 2 glasses of wine.

(3) About 2 small glasses of whisky

A (1) only

B (1) and (2) only

C (2) and (3) only

D (1), (2) and (3)

7. What health problems can be caused by drinking alcohol over a long period of time?

(1) Liver damage.

(2) Heart and brain damage.

(3) Skin cancer.

A (1) only

B (1) and (2) only C (2) and (3) only

D (1), (2) and (3)

8. What social problems are associated with the drinking of alcohol?

(1) Addiction to alcohol.

(2) Family problems.

(3) Road accidents.

A (1) and (2) only

B (1) and (3) only

C (2) and (3) only

D (1), (2) and (3)

9. What is the safe limit alcohol limit for a pregnant woman?

A No alcohol at all. B 1 to 2 cans of beer a day.

C 2 to 3 cans of beer a week.

D One bottle of wine a week.

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Structured questions

1. (a) State TWO negative effects of consuming a small amount of alcohol at one time.

__E.g. Speech can become slower. Decrease in alertness (increasing the chance of an

accident).__________________________________________________________

(b) State TWO effects of consuming a large amount of alcohol at one time.

_E.g. Unable to stand. Speech becomes difficult/slurred. May become unconscious.

__________________________________________________________________

(c) List some health problems that can occur with drinking over several years.

_E.g. Damage to body organs such as the liver, brain, heart and stomach. Cancer of the

mouth, throat and gullet. High blood pressure. Weight problems/obesity.

______________________________________________________________________

(d) Why is it harmful for a pregnant woman to consume alcohol?

__The alcohol can pass through the placenta from the mother to the unborn child. The

alcohol can damage the baby ’ s body and brain. _____________________________

(e) List some social problems associated with alcohol.

_E.g. People can become addicted to alcohol. A heavy drinker can be aggressive to his

family. Some people with alcohol problems commit crimes.

______________________________________________________________________

2. (a) What is meant by ‘blood alcohol level (or concentration)’?

__The mass of alcohol (in milligrams) present in 100 cm 3 of blood. _________________

(b) What happens to this level as a person continues to drink?

__The level/concentration increases.__________________________________________

(c) (i) For driving in Hong Kong, what is the legal limit for blood alcohol level?

__50 mg/100 cm 3 ________________________________________________________

(ii) Give an example of how much alcohol can be consumed within an hour to reach this

level?

__E.g. 2 to 3 cans of beer. / 2 glasses of wine.__________________________________

(iii) What is the instrument used by the Police to check a person’s blood alcohol level?

___A breathalyser.________________________________________________________

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