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

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Methanoic acid and ethanol react in the presence of an acid to form an ester. 

Name the ester that will be formed. 

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This question is about the reactions of carboxylic acids.

Carboxylic acids react with solutions of metal carbonates.

i) Complete the chemical equation for the reaction of ethanoic acid, CH₃COOH, with potassium carbonate solution.

2CH₃COOH + K₂CO₃ →............................... + ....................... + ........................

(2)

ii) State what you would see in this reaction.

(1)

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The ester, ethyl ethanoate, can be prepared by reacting ethanol with ethanoic acid.

This is the method for the preparation.

• mix equal amounts of ethanoic acid and ethanol in a boiling tube

• add a few drops of concentrated sulfuric acid

• place the boiling tube in a hot water bath for several minutes

i) State the role of concentrated sulfuric acid in this reaction.

(1)

ii) Suggest why the mixture is heated in a water bath rather than directly with a Bunsen burner flame.

(1)

iii) State how you would know that ethyl ethanoate has formed.

(1)

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Another ester, methyl propanoate, can be prepared by reacting methanol with propanoic acid.

i) Draw the displayed formulae of methanol, propanoic acid and the ester, methyl propanoate.

(3)

ii) Give the name of the other product of this reaction.

(1)

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Give one use of esters.

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Ethyl ethanoate can be prepared by heating a mixture of ethanoic acid, ethanol and concentrated sulfuric acid.

Which statement about this reaction is not correct? 

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Propanoic acid reacts with ethanol in an esterification reaction. 

What is the displayed formula of the ester that is formed during this reaction?

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Ethanol, C₂H₅OH, can be oxidised to produce ethanoic acid, CH₃COOH, by heating it with potassium dichromate(VI).

 i) Name one other reactant needed for this reaction to occur.

(1)

ii) Which colour change occurs during this reaction?

(1)

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When ethanol is burned in air, complete combustion can occur. The equation for this reaction is:

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

This equation can also be written using displayed formulae to show all the covalent bonds in the molecules.

The table gives the bond energies for these bonds.

i) Use values from the table to calculate the energy needed to break all the bonds in the reactants.

(2)

energy needed .............................................................. kJ

ii) Use values from the table to calculate the energy released when all the bonds in the products are formed.

(2)

energy released .............................................................. kJ

iii) Calculate the molar enthalpy change (ΔH) in kJ / mol, for the complete combustion of ethanol. Include a sign in your answer.

(1)

ΔH = .............................................................. kJ / mol

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Ethanol reacts with methanoic acid, HCOOH, in the presence of an acid catalyst to form an ester. 

The equation for the reaction is:

 C₂H₅OH + HCOOH  HCOOC₂H₅ + H₂O

 i) Give the name of the ester that forms.

 (1)

 ii) Draw the displayed formula for this ester.

 (2)

iii) When this reaction takes place in a sealed container, the reaction can reach dynamic equilibrium.

 Give two characteristics of a reaction at dynamic equilibrium.

 (2)

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Methanoic acid reacts with sodium carbonate to form sodium methanoate, carbon dioxide and water. 

The equation for the reaction is: 

2HCOOH + Na₂CO₃ → 2HCOONa + CO₂ + H₂O 

Calculate the volume, in cm³ , of carbon dioxide gas produced when 2.3 g of methanoic acid reacts completely with sodium carbonate. 

[M_r of HCOOH = 46] 

[Molar volume of carbon dioxide at rtp = 24 dm³]

 volume of carbon dioxide = .............................................................. cm³

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This question is about esters.

Ester A reacts with water to form ethanoic acid and ethanol.

The displayed formulae of the reactants and products are shown in this equation

The molar enthalpy change (ΔH) for the reaction is 0 kJ / mol.

i) Draw a ring around the functional group in ester A.

 (1)

 ii) Give the name of ester A.

 (1)

 iii) Describe a chemical test, other than using an indicator, to show that the reaction mixture contains ethanoic acid.

 (2)

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Explain why the molar enthalpy change (ΔH) for the reaction between ester A and water is 0 kJ / mol. 

In your answer, refer to the bonds broken and the bonds formed.

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A mixture of ester A and water is left in a sealed container until the reaction mixture reaches dynamic equilibrium.

 i) Describe what is meant by dynamic equilibrium.

 (2)

 ii) Explain why adding a catalyst does not change the position of equilibrium.

 (2)

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The ethanoic acid produced in the reaction is completely neutralised by 22.75 cm³ of 0.150 mol / dm³ barium hydroxide solution. 

The equation for the neutralisation reaction is

2CH₃COOH + Ba(OH)₂ → Ba(CH₃COO)₂ + 2H₂O 

Calculate the amount, in moles, of ethanoic acid neutralised. 

Give your answer to 3 significant figures.

  amount = .............................. mol

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The structures of two organic compounds are shown.

These compounds react together to form a polymer. 

Give the repeat unit of the polymer formed.

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Esters are organic chemicals noted for their characteristic smells. A carboxylic acid and an alcohol will react to form an ester.

Draw the displayed formula of each of the following. Show all the bonds in the structure.

i) ethanoic acid

(1)

ii) ethanol

(1)

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Ethanoic acid and ethanol react to form an ester.

i) What is the name of this ester?

(1)

ii) The same linkage is found in polyesters. Draw the structure of the polyester which can be formed from the monomers shown below.

HOOC—C₆H₄—COOH and HO—CH₂—CH₂—OH

(3)

iii) Describe the pollution problems caused by non-biodegradable polymers.

(1)

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Ethanoic acid and methanol will react to form a different ester.

i) Name the catalyst needed to form an ester from ethanoic acid and methanol.

(1)

ii) Name the ester formed when ethanoic acid reacts with methanol.

(1)

iii) Give the structural formula of the ester formed when ethanoic acid reacts with methanol. 

(1)

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The ester methyl butanoate is found in apples. It can be made from butanoic acid and methanol. Their structural formulae are given below. 

butanoic acid	methanol

 Calculate the relative molecular mass of methyl butanoate.

(A_r: C = 12, H = 1, O = 16)

 Relative molecular mass .....................................................

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An ester has the structural formula CH₃COOCH₂CH₂CH₃.

i) Draw out the displayed formula and circle the functional group.

(2)

ii) State the name of the alcohol used to make this ester.

(1)

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The ester CH₃(CH₂)₂COOCH₃ is an ester found in apples and contributes to their smell.

This ester can be prepared in the laboratory from a carboxylic acid and an alcohol.

Write a balanced equation for the production of CH₃(CH₂)₂COOCH₃.

An ester, X, was found to contain 39.98% carbon and 6.65% hydrogen.

Show that ester X is not the ester with the formula CH₃(CH₂)₂COOCH₃.

The molecular mass of ester X is 60.

Deduce the molecular formula of ester X.

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A sweet-smelling ester with the empirical formula C₂H₄O was produced.

Which of the following reactants could not have been used to produce this ester?

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During the preparation of an ester, the reactants are added to a flask and heated using a water bath.

Explain how and why the ester is separated from the reaction mixture.

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A carboxylic acid, Y, was used to form a polyester. The relative formula mass of the carboxylic acid was found to be 90 and its empirical formula is CHO₂.

i) Deduce the molecular formula of carboxylic acid Y.

(2)

ii) Draw the displayed formula of the carboxylic acid, Y.

(2)

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Carboxylic acid Y reacted with alcohol Z to form a polyester.

Give the formula of the other product in this reaction.

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An ester was produced in the following reaction between methanoic acid and butanol.

HCOOH + C₄H₉OH  HCOOC₄H₉ + H₂O

After a period of time, the reaction reaches dynamic equilibrium.

Explain what is meant by the term dynamic equilibrium. 

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i) Give the name of the ester produced during the reaction between methanoic acid and butanol.

(1)

ii) State the necessary catalyst for the reaction.

(1)

4.60 g of methanoic acid was added to 9.62 g of butanol.

Calculate the maximum mass of ester that could be produced from this reaction.

The percentage yield of the reaction was found to be 68.6%.

Determine the mass of ester produced.

Give your answer to 3 significant figures.