Edexcel IGCSE Chemistry

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IGCSEChemistryEdexcelTopic Questions4. Organic Chemistry4.6 Carboxylic acids

4.6 Carboxylic acids

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11 mark

Separate: Chemistry Only

Ethanoic acid is a member of the homologous series of carboxylic acids.

Which is the functional group of carboxylic acids?




 ☐ A alkene-functional-group



☐ B ester-functional-group



☐ C alcohol-functional-group



☐ D carboxylic-acid-functional-group

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21 mark

Separate: Chemistry Only

The formula for ethanoic acid can be written in different ways:

4-6-q2-edexcel-igcse-chemistry

What are the correct names for the different ways to represent formulae?

      Formula 1 Formula 2 Formula 3
  ☐ A molecular formula structural formula displayed formula
  ☐ B structural formula molecular formula displayed formula
  ☐ C molecular formula empirical formula structural formula
  ☐ D empirical formula structural formula molecular formula

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31 mark

Separate: Chemistry Only

Solutions of carboxylic acids react with magnesium to form a salt and hydrogen gas.

Using the apparatus and method below, a student investigates how the time to collect 20 cm3 of hydrogen gas varies with different carboxylic acid solutions. 

4-6-q3-edexcel-igcse-chemistry

Method:

  • pour the carboxylic acid solution into a conical flask
  • add some magnesium into the carboxylic acid solution
  • immediately connect the gas syringe and start a timer
  • record the time taken to collect 20 cm3 of hydrogen gas
  • repeat for different carboxylic acid solutions

Which of the following is not a variable that should be controlled?

  ☐ A The mass of magnesium
  ☐ B The volume of acid
  ☐ C The type of acid
  ☐ D The concentration of acid

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4a1 mark

Separate: Chemistry Only

The structures of two carboxylic acids are shown below. 

4-6-4a-e-4-6-q4-carboxylic-acid-image

What is the name of carboxylic acid B?

  ☐ A butanoic acid 
  ☐ B propanoic acid
  ☐ C ethanoic acid
  ☐ D methanoic acid 

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4b1 mark

Separate: Chemistry Only

Give one use of carboxylic acid A.

  ☐ A vinegar
  ☐ B fuel
  ☐ C smelling salts
  ☐ D polymer

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4c2 marks

Separate: Chemistry Only

Both carboxylic acids A and B can react with metal carbonates to produce a salt and two other products. 

Name the two other products formed. 

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4d1 mark

Carboxylic Acids A and B will also react with metals to form hydrogen gas. 

Which row in the table correctly shows the test and result for this gas?

  ☐ A test: glowing splint   result: relights 
  ☐ B test: burning splint   result: squeaky pop sound
  ☐ C test: glowing splint   result: squeaky pop sound
  ☐ D test: burning splint  result: flame extinguished 

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5a1 mark

Separate: Chemistry Only

Butanoic acid belongs to the homologous series carboxylic acids. 

Complete the structure of butanoic showing all bonds.


4-6-5a-e-4-6-q5a-c-equals-o-bond-a

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5b1 mark

Explain why butanoic acid is a saturated compound. 

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5c1 mark

Separate: Chemistry Only

Butanoic acid can react with magnesium carbonate to form a salt, carbon dioxide and water. 

What type of reaction is this?

  ☐ A thermal decomposition
  ☐ B neutralisation
  ☐ C combustion
  ☐ D endothermic 

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5d1 mark

Separate: Chemistry Only

Butanoic acid can also react with a metal. 

Complete the word equation for this reaction.

__________  +   butanoic acid   →    sodium butanoate +  ____________

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1a3 marks

This question is about carboxylic acids.

Solutions of carboxylic acids react with magnesium metal to form hydrogen gas.

A student uses this apparatus to investigate the time taken to produce 10 cm3 of hydrogen gas from different carboxylic acids.

FYXWwpM8_2021-ja2c-q3a

This is the student’s method.

  • pour some carboxylic acid solution into a conical flask
  • add some magnesium powder
  • quickly connect the gas syringe and start a timer
  • record the time taken to collect 10 cm3 of hydrogen gas

The student repeats the method with three other carboxylic acids.

i)
All the carboxylic acids are of the same concentration.
Give two other variables the student should control in his investigation.

(2)

ii)
Give a reason why it is important to connect the gas syringe quickly.

(1)

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1b
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The table shows the student’s results.

    Time taken to produce 10 cm3 of hydrogen in s
Carboxylic
acid		 Formula of
carboxylic acid		 Experiment
1		 Experiment
2		 Experiment
3		 Experiment
4		 Mean
time
Methanoic
acid		 HCOOH 48 50 47 49 49
Ethanoic
acid		 CH3COOH 61 63 60 61 61
Propanoic
acid		 CH3CH2COOH 69 93 70 71  
Butanoic
acid		 CH3CH2CH2COOH 83 85 82 81 83

i)
Calculate the mean (average) time for propanoic acid to produce 10 cm3 of hydrogen gas.

(2)


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

ii)
Deduce the relationship between the number of carbon atoms in the molecule and the time taken to produce 10 cm3 of hydrogen gas.

(1)

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1c2 marks

Separate: Chemistry Only

An ester is formed by adding ethanoic acid to ethanol in the presence of sulfuric acid.

Give the displayed formula of the ester produced when ethanoic acid reacts with ethanol.

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2a1 mark

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This question is about the reactions of organic compounds A - E shown in Figure 1. 


Figure 1 

organic-compounds-displayed-formulae
 

Name compound C. 

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2b2 marks

Separate: Chemistry Only

Name the two products formed when E reacts with sodium.

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2c1 mark

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Which compound reacts with compound A to produce compound C? 

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2d1 mark

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Which compound dissolves in water to produce a neutral solution?

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3a1 mark

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Alcohol A has the structural formula, CH3CH2OH.

Which product is formed when alcohol A is oxidised using acidified potassium dichromate (VII)?

  ☐ A CH3CH2COOH
  ☐ B C2H4O2
  ☐ C HCOOCH3
  ☐ D C2H6O

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3b2 marks

Separate: Chemistry Only

When alcohol A reacts with propanoic acid, an ester, B is formed. 

CH3CH2OH + CH3CH2COOH → B + H2O

Give the name and structural formula of B.

Name ............................................................................
Structural formula ............................................................................

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3c3 marks

Separate: Chemistry Only

Propanoic acid reacts with sodium carbonate.

Write the balanced symbol equation for the reaction.

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3d
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Propanoic acid also reacts with magnesium 

2CH3CH2COOH (aq) + Mg (s) → (CH3CH2COO)2Mg (aq)  + H2 (g) 

An excess of magnesium was added to 50 cm3 of 1.0 mol / dm3 and the hydrogen gas produced was collected in a gas syringe. 

Calculate the volume, in cm3, of hydrogen gas produced in this reaction.

 
 
Volume of hydrogen gas collected .................................................... cm3

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4a5 marks

Separate: Chemistry Only

Propanoic acid is a carboxylic acid. Its formula is CH3–CH2–COOH.

 
i)
Propanoic acid is the third member of the homologous series of carboxylic acids.
 
Give the name and structural formula of the fourth member of this series.
 
Name ..............................................................
 
Formula ..............................................................

(2)

ii)
Members of a homologous series have very similar chemical properties.
 
State three other characteristics of a homologous series.

(3)

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4b3 marks

Separate: Chemistry Only

Carboxylic acids can be made by the oxidation of alcohols.

 
i)
Draw the structural formula of the alcohol which can be oxidised to propanoic acid.
Show all atoms and bonds.

(1)

ii)
Name a reagent, other than oxygen, which can oxidise alcohols to carboxylic acids.

(2)

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4c4 marks

Separate: Chemistry Only

Complete the following equations for some of the reactions of propanoic acid.

 
i)
Zinc + propanoic acid → .................. .................. + hydrogen
 
(1)
 
ii)
Calcium oxide + propanoic acid → .................. + ..................
 
(1)
 
iii)
LiOH + CH3CH2COOH →  .................. + ..................
 
(1)
 
iv)
......CaCO3 + ......C2H5COOH →  .................. + .................. +  ..................
 
(1)

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4d7 marks

A piece of magnesium was added to 100 cm3 of an aqueous acid. The time taken for the metal to react completely was measured. 

This experiment was repeated using different aqueous acids. The same volume of acid was used in each experiment and the pieces of magnesium used were identical. 

In one experiment the reaction was carried out at a different temperature.

 
experiment acid concentration in mol/dm3 temperature / °C time / seconds
A propanoic 1.0 20 300
B propanoic 1.0 30 180
C propanoic 0.5 20 480
D hydrochloric 1.0 20 60
 

Explain the following in terms of collision rate between reacting particles.

 
i)
Why is the rate in experiment C slower than the rate in experiment A? 

(2)

ii)
Why is the rate in experiment B faster than the rate in experiment A?

(2)

iii)
Why is the rate in experiment D faster than the rate in experiment A?

(3)

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5a3 marks

Separate: Chemistry Only

Carboxylic acids contain the group

4-6-5a-h--cooh

Ethanoic acid is a typical carboxylic acid. It forms ethanoates.

Complete the following equations.

Mg + ......CH3COOH → ............................... + ...............................

(2)

sodium hydroxide + ethanoic acid → ........................  ........................ + ........................

(1)

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5b2 marks

Separate: Chemistry Only

Ethanoic acid reacts with ethanol to form an ester. Give the name of the ester and draw its displayed formula. Show all of the bonds.

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5c
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Maleic acid is an unsaturated acid. 5.8 g of this acid contained 2.4 g of carbon, 0.2 g of hydrogen and 3.2 g of oxygen.

i)
How do you know that the acid contained only carbon, hydrogen and oxygen?
 
(1)
ii)
Calculate the empirical formula of maleic acid.
 
Number of moles of carbon atoms = ................................
 
Number of moles of hydrogen atoms = ................................
 
Number of moles of oxygen atoms = ................................
 
The empirical formula is ......................................................................................
 

(3)

iii)
The mass of one mole of maleic acid is 116 g. What is its molecular formula?
 

(2)

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5d
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Separate: Chemistry Only

Maleic acid is dibasic. One mole of acid produces two moles of H+. Deduce its structural formula.

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11 mark

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Butanoic acid behaves like other acids.

Which is the correct statement about the reactions of butanoic acid?

  ☐ A It reacts with sodium hydroxide in a neutralisation reaction to form a salt and hydrogen gas
  ☐ B In a reaction with calcium carbonate, a salt and water are formed
  ☐ C It reacts with calcium to form a salt and oxygen gas
  ☐ D When it reacts with magnesium carbonate, fizzing is observed

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2a3 marks

Separate: Chemistry Only

This question is about alcohols, carboxylic acids and their reactions.

The boxes give some information about a carboxylic acid.

Complete the boxes by giving the missing information.

structural formula CH3COOH
name  
  CH2O
displayed formula  

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2b3 marks

Separate: Chemistry Only

Ethanol can be oxidised to produce a carboxylic acid.

i)
Give the names of the two reagents used in this oxidation reaction.

(2)

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

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

ii)
Which of these colour changes occurs during the reaction?

(1)

  ☐ A green to orange
  ☐ B orange to green
  ☐ C red to yellow
  ☐ D yellow to red

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2c2 marks

Separate: Chemistry Only

Alcohols and carboxylic acids can be heated together to form esters.

i)
State why it is better to heat the mixture using a water bath rather than directly with a Bunsen burner flame.

(1)

ii)
An ester has the structural formula CH3CH2COOCH3

Which of these is the name of this ester?

(1)

  ☐ A ethyl methanoate
  ☐ B methyl ethanoate
  ☐ C methyl propanoate
  ☐ D propyl methanoate

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31 mark

What is the empirical formula of butanoic acid?

  ☐ A C3H7COOH
  ☐ B C4H8O2
  ☐ C C2H4O
  ☐ D C2H4O2

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4a2 marks

Methanoic acid is the first member of the homologous series of carboxylic acids.

Give two general characteristics of a homologous series.

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4b5 marks

Separate: Chemistry Only

In some areas when water is boiled, the inside of kettles become coated with a layer of calcium carbonate. This can be removed by adding methanoic acid.

i)
Complete the equation.

............ HCOOH + CaCO3 → Ca(HCOO)2 + ................. + .................

(2)

ii)
Methanoic acid reacts with most metals above hydrogen in the reactivity series.
Complete the word equation.

zinc + methanoic acid → ............................................ + ............................................

(2)

iii)
Aluminium is also above hydrogen in the reactivity series.
Why does methanoic acid not react with an aluminium kettle?

(1)

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4c2 marks

Separate: Chemistry Only

Draw the displayed formula for the ester formed when methanoic acid reacts with ethanol. 

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4d3 marks

Separate: Chemistry Only

Give the name, molecular formula and empirical formula of the fourth acid in this series.


name ...........................................................................................................................

(1)

molecular formula .......................................................................................................

(1)

empirical formula ........................................................................................................

(1)

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5a1 mark

Separate: Chemistry Only

Ethanoic acid is a carboxylic acid used in vinegar. 

Which of these statements is true about ethanoic acid?

  ☐ A It reacts with propanol to form ethyl propanoate 
  ☐ B Its molecular formula is C2H5O2
  ☐ C It follows the general formula CnH2nCOOH
  ☐ D It reacts with magnesium to form magnesium ethanoate

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5b3 marks

Separate: Chemistry only

When a bottle of wine is left open, ethanoic acid and water can form as a result of ethanol reacting with the oxygen in the air.

i)
Complete the equation for this reaction.


......................  +   O2. →    CH3COOH   + ........................

(2)

ii)
Which calculation shows the percentage by mass of hydrogen in ethanoic acid?

(Ar of hydrogen, H = 1, Mr of ethanoic acid, CH3COOH = 60)
(1)
  ☐ A 1 over 60 cross times 100
  ☐ B 3 over 60 cross times 100
  ☐ C 4 over 60 cross times 100
  ☐ D begin mathsize 14px style 60 over 1 cross times 100 end style



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5c3 marks

Separate: Chemistry Only

Propanoic acid, C2H5COOH,  belongs to the same homologous series as ethanoic acid. 


It can react with sodium hydroxide to form sodium propanoate, C3H5NaO2 and water. 

i)
Draw the structure of a molecule of propanoic acid, showing all covalent bonds. 

(2)
ii)
Write a balanced symbol equation for the reaction between propanoic acid and sodium hydroxide.

(1)

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5d2 marks

Describe a chemical test that could be done to show that propanoic acid is acidic. 

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