Alcohols & Carboxylic Acids (Edexcel GCSE Chemistry)

Alcohols and carboxylic acids are important organic compounds. Figure 8 shows the names and formulae of three alcohols in a homologous series.

Figure 8   

Predict the formula of the alcohol that has five carbon atoms in its molecule, using the information in Figure 8.

Calculate the relative formula mass of ethanol, C₂H₅OH.

(relative atomic masses: H = 1, C = 12, O = 16)

relative formula mass = ..............................................................

Ethanol can be oxidised to form ethanoic acid.

Draw the structure of a molecule of ethanoic acid, showing all the covalent bonds.

The temperature rise in water when liquid fuels burn can be found using the equipment shown in Figure 9.

Figure 9

i) A student compares the temperature rise produced in the water when propanol burns with the temperature rise produced when ethanol burns.

State two factors that the student must keep the same in both experiments in order to have a fair comparison.

(2)

ii) The results for the two alcohols are shown in Figure 10.

Figure 10

Explain, using only the information in Figure 10, why propanol might be the better fuel.

(2)

What is the reading on the following thermometer?

Ethanol can be used as a liquid fuel.

A student investigates how much heat energy is released when a known mass of ethanol is burned.

The apparatus is set up as shown in Figure 15.

A known volume of water is placed in a metal can.
The temperature of the water is measured.
The ethanol is ignited and placed under the beaker so that the flame is touching the beaker.
The water is heated by the flame.
The flame is extinguished.
The final temperature of the water is measured.

The theoretical temperature rise for burning a given mass of ethanol is 82.4 °C.

In the experiment the actual temperature rise for burning this mass of ethanol was only 34.8 °C.

One reason why the temperature rise is less than expected is that the ethanol does not burn completely.

i) Give a reason why, even if the ethanol burns completely, the actual temperature rise is much less than the theoretical value.

(1)

ii) Explain how the method described above could be improved to give a temperature rise closer to the theoretical value.

(2)

iii) The amount of heat energy used to raise the temperature of the water by 34.8 °C can be calculated using

heat energy = 210 × temperature rise

Calculate the amount of heat energy used.

(2)

heat energy = ........................ (energy units)

Propanol and butanol are both members of the same homologous series as ethanol.

Propanol and butanol can also be burned in the apparatus shown in Figure 15.

Give three reasons why ethanol, propanol and butanol are members of the same homologous series.

reason 1 ..............................................

reason 2 ..............................................

reason 3 .............................................

Ethanol can oxidise when exposed to air to produce ethanoic acid and water. Propanol can also oxidise in a similar reaction when it is exposed to air.

i) Write the word equation for the reaction when propanol oxidises when it is exposed to air.

(2)

ii) What is the formula of the functional group in carboxylic acids?

(1)

Ethanol is produced by fermentation.

Which of the following conditions is not required to produce ethanol by fermentation?

Ethanol is made by fermentation of a carbohydrate dissolved in water, in the presence of yeast.

The reaction is carried out at 30 °C.

Explain why the reaction is carried out at a temperature of 30 °C rather than at a temperature of 80 °C.

Ethanol, C₂H₅OH, can be converted into ethanoic acid, CH₃COOH.

i) In this reaction ethanol is

(1)

ii) Draw the structure of a molecule of ethanoic acid, CH₃COOH, showing all covalent bonds.

(2)

 i) The apparatus in Figure 16 can be used to investigate the temperature rise produced in a known mass of water when a sample of ethanol is burned.

Figure 16

The first steps of the method are

1. put 100cm³ of water into a beaker

2. determine the mass of the burner containing ethanol

3. measure the initial temperature of the water

4. place the burner under the beaker of water

5. light the wick

Describe the remaining steps of the method that are needed to determine the mass of ethanol required to raise the temperature of the water by 30°C.

(3)

ii) In a different experiment, separate samples of the alcohols methanol, ethanol, propanol, butanol and pentanol were burned to determine the mass of each alcohol that needs to be burned to raise the temperature of 100 cm³ water by 10°C.

Draw a graph of the mass of each alcohol required to raise the temperature of 100 cm³ of water by 10°C against the number of carbon atoms in one molecule of that alcohol.

(3)

What are the names of compounds A and B?

Ethanol can be produced by the fermentation of glucose solution. Which of these shows the word equation for the fermentation of glucose solution?

The names and formulae of the first four alcohols in the homologous series of alcohols are given in Figure 12.

Figure 12

i) Pentanol is the next member of this series. A molecule of pentanol contains five carbon atoms.

Suggest the formula of a molecule of pentanol.

(1)

ii) Draw the structure of a molecule of ethanol. Show all bonds.

(2)

Ethanol is present in alcoholic drinks, such as wine.

When a bottle of wine is left open some of the ethanol reacts with the oxygen in the air to form ethanoic acid, CH₃COOH, and water.

i) Complete the equation for this reaction.

(2)

CH₃CH₂OH + .......................... → CH₃COOH + ........................

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

(relative atomic mass of hydrogen, H = 1,

relative formula mass of ethanoic acid, CH₃COOH = 60)

(1)

Polymers have many uses.
However, the disposal of polymers after use can be a problem.
The uses of polymers are related to their properties.
Some uses of three common polymers are given in Figure 13.

Figure 13

Discuss the reasons for using these polymers in the ways shown in Figure 13 and the problems in disposing of these polymers.

Fermentation of carbohydrates produces a dilute solution of ethanol.

This need further processing by fractional distillation to produce a concentrated solution of ethanol.

Some of the steps of fractional distillation are shown below.

The steps shown are not in the correct order.

Which of the following shows the correct order of the steps above?

This question is about alcohols.

i) Figure 14 shows an incomplete diagram of the structure of a molecule of propanol, CH₃CH₂CH₂OH.

Complete the structure of the molecule of propanol in Figure 14.

(2)

Figure 14

ii) Propanol can be converted into propanoic acid. What happens to propanol in this reaction?

(1)

A student used an alcohol burner to find the mass of different alcohols needed to raise the temperature of 100 cm³ of water by 20 °C.

Figure 15 shows their results.

Figure 15

i) Calculate the mass of butanol used.

(1)

mass of butanol = ................... g

ii) Figure 16 shows equipment that can be used to obtain the results shown in Figure 15.

Figure 16

Describe an experiment, using the equipment in Figure 16, that could be used to obtain results like those shown in Figure 15.

(6)

iii) The results show that 0.36 g of pentanol was needed to raise the temperature of the water by 20 °C.

Calculate the mass of pentanol needed to raise the temperature of water by 1 °C.

Give your answer to 2 decimal places.

Show your working.

(2)

Which of the following statements about butanol is not correct?

Figure 10 shows a flask fitted with a cotton wool plug. The flask contains an aqueous solution of a carbohydrate.

Figure 10

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 in Figure 11 is used to increase the concentration of the dilute solution of ethanol.

Figure 11

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 a carbohydrate is

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

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

(relative formula masses: CO₂= 44; C₆H₁₂O₆= 180)

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

Figure 12 shows information about some compounds in the same homologous series.

Figure 12

Explain, using the data in Figure 12, why these compounds belong together in the same homologous series.

Propanol, C₃H₇OH, can undergo reactions to form compounds Y and Z shown in Figure 14.

Figure 14

i) What happens to propanol when it forms compound Y?

(1)

ii) Compound Y can also be formed in the following reaction

Explain how bromine water can be used to distinguish between compound X and compound Y.

(3)

iii) Compound Z is a carboxylic acid. Which of the following shows the functional group of a carboxylic acid? (1)

☐	A
☐	B
☐	C
☐	D

iv) Compound Z is an acid and turns litmus and universal indicator papers red.
Compound Z also shows other acidic properties.

Devise an experiment that would show another acidic property of compound Z.

(2)

Higher Only

The balanced equation for the production of ethanol from the carbohydrate sucrose is

+ 

Calculate the minimum mass of sucrose needed to produce 26.9 g of ethanol.

(relative formula masses: )

minimum mass of sucrose = ................................. g

Higher Only

Calculate the total number of atoms in 10.0 g of sucrose, C₁₂H₂₂O₁₁.

(relative formula mass: C₁₂H₂₂O₁₁ = 342; Avogadro constant = 6.02 × 10²³)

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

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)

Carboxylic acids can be made by the oxidation of alcohols.

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

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

i) Zinc + propanoic acid → .................. .................. + hydrogen

(1) 

ii) Calcium oxide + propanoic acid → .................. + ..................

(1) 

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.

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)

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)

Higher Only

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)

This question is about carboxylic acids.

The table below shows information about three carboxylic acids.

Complete the table. 

Higher Only

Solutions of ethanoic acid and hydrochloric acid have different pH levels at the same concentration.

Explain the difference in pH levels between the two acids 

A student adds sodium to a solution of ethanoic acid in an open flask on a balance.

Explain what happens to the mass of the flask and its contents during the reaction.

In a separate reaction, a student adds ethanoic acid to zinc carbonate.

Describe and give the result of a test the student would do to identify the gas produced.