Alcohols (Edexcel IGCSE Chemistry (Modular): Unit 2)

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Grapes contain glucose that can be fermented to make ethanol.

The grapes are collected and crushed to produce an aqueous solution containing glucose. Yeast is added to the solution and the mixture is left to ferment at a temperature of about 30 °C in the absence of air.

i) State why yeast is added.

(2)

ii) Explain why another organic compound may also be formed if fermentation is carried out in the presence of air.

(2)

iii) Explain why 30 °C is considered to be an optimum temperature for this reaction.

(2)

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Ethanol can also be manufactured by reacting ethene with steam.

i) Write the chemical equation for this reaction.

(1)

ii) Name the type of reaction that occurs.

(1)

iii) State two conditions used for this reaction in industry.

(2)

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Grapes also contain esters. The formula of an ester is shown.

Deduce the name of the carboxylic acid and the alcohol that can react together to make this ester.

carboxylic acid .................................................................................... alcohol ....................................................................................

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Butanol is a member of the homologous series of alcohols.

Which of the following is not a formula of butanol?

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Methanol, ethanol, propanol and butanol are alcohols. They are all liquids that evaporate easily when warmed. A student uses this apparatus to compare the time taken for the four liquids to evaporate.

She uses this method:

• pour some methanol into an evaporating basin

• place the evaporating basin on top of a beaker containing hot water

• measure the time taken for the methanol to evaporate completely

• repeat the experiment with each of the other alcohols, using the same apparatus

State two variables the student should control to make sure her results are valid.

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State why it is not safe to heat the evaporating basin directly with a Bunsen flame.

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The table shows the results of experiments done by four students, A, B, C and D.

i) Calculate the mean (average) time for butanol to evaporate.

mean time = ..............................................................s

(2)

ii) Explain how the results show which alcohol evaporates most easily.

(2)

iii) State the relationship between the number of carbon atoms in the molecule and how easily the alcohol evaporates.

(2)

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Which of the following reactions does not involve the oxidation of ethanol?

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Some cars in Brazil use ethanol, C₂H₅OH, as a fuel instead of petrol. The ethanol is made by the fermentation of glucose which is obtained from sugar cane. The sugar is extracted from the sugar cane and then dissolved in water to make a sugar solution.

i) Name the substance that is added to the sugar solution that causes glucose to ferment.

(1)

ii) Which temperature is the most suitable for fermentation?

(1)

iii) Explain why fermentation is done in the absence of air.

(2)

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i) State what is meant by the term fuel.

(1)

ii) Write a chemical equation for the complete combustion of ethanol in air.

(2)

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Ethanol is also manufactured by reacting steam with ethene, C₂H₄

The equation for this reaction is:

C₂H₄ (g) + H₂O (g) → C₂H₅OH (g)

State the conditions of temperature and pressure used in this process.

temperature .......................................

pressure ...............................................

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When ethanol is heated with acidified potassium dichromate(VI), it is oxidised to ethanoic acid.

i) State the colour change that occurs in the potassium dichromate(VI) during this reaction.

from .........................................................to ...............................................

(1)

ii) The structural formula of ethanoic acid is CH₃COOH.

Draw the displayed formula of ethanoic acid.

(2)

iii) Complete the equation for the reaction of ethanoic acid with sodium.

.......CH₃COOH (aq) + .........Na (s) → .......................... (aq) + .......................... (g)

(2)

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Alcohols contain the functional group —OH

Give the structural formula of the alcohol that contains one carbon atom.

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Ethanol (C₂H₅OH) is an alcohol that can be obtained from glucose (C₆H₁₂O₆).

i) Name the process that converts glucose into ethanol.

(1)

ii) Explain why this process is carried out in the absence of air and at a temperature below 40 °C.

(4)

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The table gives information about some organic compounds in the same homologous series.

Compound	Molecular formula	Displayed formula
ethanoic acid	C2H4O2
propanoic acid
	C4H8O2

i) Complete the table by giving the missing information.

(3)

ii) Name the homologous series that contains these compounds.

(1)

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The compounds in the table can react with alcohols to form esters.

When preparing esters, a small amount of concentrated sulfuric acid is also used.

i) State the purpose of the acid.

(1)

ii) Draw the displayed formula of the ester that forms when propanoic acid reacts with ethanol.

(2)

iii) Esters have particular uses that depend on their properties. Give an example of a property and use of esters.

(2)

   property .....................................................................................................

   use ..........................................................................................................

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This question is about alcohols, carboxylic acids and esters.

The table gives information about some alcohols.

Complete the table by giving the missing information

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Ethanol can be oxidised to ethanoic acid by heating with potassium dichromate(VI) and another reagent.

i) Name the other reagent.

(1)

ii) State the colour change that occurs during this reaction.

(1)

   from ........................................ to ................................................

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Alcohols react with carboxylic acids to form esters.

i) Name the ester that forms when ethanol reacts with ethanoic acid.

(1)

ii) Complete the equation for the reaction between methanol and ethanoic acid.

(2)

CH₃OH + ......................................→ .............................................. + H₂O

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Ethanol, C₂H₅OH, can be manufactured from ethene and steam using a phosphoric acid catalyst.

  i) State the temperature and pressure used in this manufacturing process.

temperature ................................................................................................ pressure ........................................................................................................

(2)

ii) Draw the displayed formula of ethanol.

(1)

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Ethanol burns in a plentiful supply of air to form carbon dioxide and water.

i) Give the chemical equation for this reaction.

(2)

ii) When the air supply is limited, incomplete combustion occurs and carbon monoxide forms.
State why carbon monoxide is poisonous to humans.

(1)

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When ethanol reacts with ethanoic acid, an ester forms.

Give the name of this ester.

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Butanedioic acid and ethanediol react together to form a polyester and water.

i) Give the name of this type of polymerisation.

(1)

ii) Complete the equation.
Show only one repeat unit of the polyester.

(3)

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Ethanol, C₂H₅OH, is a member of the homologous series of alcohols.

Give two characteristics of a homologous series.

1. ................................................................

2. ................................................................

When ethanol is heated with potassium dichromate(VI) and one other reagent, the ethanol is oxidised to ethanoic acid, CH₃COOH.

i) Give the formula of the other reagent.

(1)

ii) State the colour change that occurs during this oxidation reaction.

(2)

from ............................to ..........................

iii) Draw the displayed formulae for ethanol and ethanoic acid in the boxes.

(2)

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Ethanol can be manufactured by two different methods. The table gives some information about the two methods.

i) Discuss the advantages and disadvantages of these two methods, using information from the table.

(6)

ii) The word equation for the fermentation process is

glucose → ethanol + carbon dioxide

Complete the chemical equation for this reaction.

(1)

C₆H₁₂O₆ → ...................................+ .......................................

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Ethanol, C₂H₅OH, can be produced by the fermentation of glucose, C₆H₁₂O₆

i) Complete the equation for the fermentation of glucose.

(1)

C₆H₁₂O₆  → 2C₂H₅OH + 2 ........................................

ii) State why it is necessary for fermentation to be done in the absence of air.

(1)

iii) Explain why the temperature should not be higher than 40 °C.

(2)

iv) When 4 mol of glucose is fermented, a mass of 55.2 g of ethanol is produced. Show that the percentage yield of ethanol is 15%. [M_r of C₂H₅OH = 46]

(2)

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Ethanol can also be produced by the reaction between ethene and steam. The equation for the reaction is

C₂H₄ (g) + H₂O (g)  C₂H₅OH (g)

i) This reaction is in dynamic equilibrium. Give two features of a reaction in dynamic equilibrium.

(2)

ii) When the equilibrium mixture is heated, the yield of ethanol decreases. Explain whether the forward reaction is exothermic or endothermic.

(2)

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Carboxylic acids react with alcohols to form esters. The displayed formula of an ester is

i) Carboxylic acid A and alcohol B react to produce this ester. Give the displayed formula of carboxylic acid A and of alcohol B.

(2)

ii) Indicators can be used to test for carboxylic acids. Describe a different chemical test for a carboxylic acid.

(2)

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Ethanol can be produced from an aqueous solution of a carbohydrate, such as glucose.

The diagram below shows a flask fitted with a cotton wool plug. The flask contains an aqueous solution of a carbohydrate.

i) State two steps that need to be taken to turn the solution of the carbohydrate in the flask into a solution of ethanol.

(2)

ii) The apparatus shown in the diagram below is used to increase the concentration of the dilute solution of ethanol.

This apparatus did not produce a very concentrated solution of ethanol. Describe how the apparatus can be altered to produce a more concentrated solution of ethanol.

(2)

The equation for the fermentation of the carbohydrate glucose, C₆H₁₂O₆, is

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Calculate the maximum mass of carbon dioxide that could be produced if 135 g of this carbohydrate is fully fermented

(M_r:    CO₂ = 44;    C₆H₁₂O₆ = 180)

mass of carbon dioxide = ............................... g

Sucrose is another type of carbohydrate that can be used to produce alcohols. Calculate the total number of atoms in 10.0 g of sucrose, C₁₂H₂₂O₁₁.
(M_r: C₁₂H₂₂O₁₁ = 342; Avogadro constant = 6.02 × 10²³)

number of atoms = ......................................

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Alcohols can be produced in a number of different ways.

Methanol can be made from a mixture of carbon monoxide and hydrogen.

CO (g) + 2H₂ (g) CH₃OH (g)

The forward reaction is exothermic.

i) Explain why the concentration of methanol at equilibrium does not change.

(2)

ii) Suggest conditions, in terms of temperature and pressure, which would give a high yield of methanol.

(2)

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This question is about alcohols. 

Alcohols have the general formula C_nH_2n+1OH.

Draw the displayed formula of propanol. 

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Deduce the molecular formula of the alcohol that has a relatvie molecular mass of 102.

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Alcohols undergo combustion reactions. 

Write a balanced symbol equation for the complete combustion of butanol. 

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Describe the conditions needed to convert ethene to ethanol.