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4.6 Carboxylic acids
Question Paper
Course Edexcel IGCSE Chemistry
Section 4. Organic Chemistry
Topic 4.6 Carboxylic acids
Difficulty Hard
Time allowed: 70
Score: /54
Percentage: /100
Page 1 of 13
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Question 1a
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.
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)
[3 marks]
Page 2 of 13
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Question 1b
The table shows the student’s results.
Time taken to produce 10 cm3 of hydrogen in s
Carboxylic Formula of Experiment Experiment Experiment Experiment Mean
acid carboxylic acid 1 2 3 4 time
Methanoic
HCOOH 48 50 47 49 49
acid
Ethanoic
CH3COOH 61 63 60 61 61
acid
Propanoic
CH3CH2COOH 69 93 70 71
acid
Butanoic
CH3CH2CH2COOH 83 85 82 81 83
acid
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)
[3 marks]
Question 1c
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.
[2 marks]
Page 3 of 13
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Question 2a
Separate: Chemistry Only
This question is about the reactions of organic compounds A - E shown in Figure 1.
Figure 1
Name compound C.
[1 mark]
Question 2b
Separate: Chemistry Only
Name the two products formed when E reacts with sodium.
[2 marks]
Question 2c
Separate: Chemistry Only
Which compound reacts with compound A to produce compound C?
Page 4 of 13
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[1 mark]
Question 2d
Separate: Chemistry Only
Which compound dissolves in water to produce a neutral solution?
[1 mark]
Question 3a
Separate: Chemistry Only
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
[1 mark]
Question 3b
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 ............................................................................
[2 marks]
Page 5 of 13
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Question 3c
Separate: Chemistry Only
Propanoic acid reacts with sodium carbonate.
Write the balanced symbol equation for the reaction.
[3 marks]
Question 3d
Separate: Chemistry Only
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
[3 marks]
Page 6 of 13
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Question 4a
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)
[5 marks]
Page 7 of 13
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Question 4b
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)
[3 marks]
Page 8 of 13
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Question 4c
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)
[4 marks]
Page 9 of 13
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Question 4d
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.
concentration in
experiment acid temperature / °C time / seconds
mol/dm3
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)
[7 marks]
Page 10 of 13
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Question 5a
Separate: Chemistry Only
Carboxylic acids contain the group
Ethanoic acid is a typical carboxylic acid. It forms ethanoates.
Complete the following equations.
Mg + ......CH3COOH → ............................... + ...............................
(2)
sodium hydroxide + ethanoic acid → ........................ ........................ + ........................
(1)
[3 marks]
Question 5b
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.
[2 marks]
Page 11 of 13
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Question 5c
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)
[6 marks]
Page 12 of 13
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Question 5d
Separate: Chemistry Only
Maleic acid is dibasic. One mole of acid produces two moles of H+. Deduce its structural formula.
[2 marks]
Page 13 of 13
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