GCSE Edexcel Chemistry Combustion of alcohols: Ethanol can be used as a liquid

Question

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 3.

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.

(a) 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.

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

(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 x temperature rise
Calculate the amount of heat energy used.

(b) 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 3.
Give three reasons why ethanol, propanol and butanol are members of the same homologous series.

(c) 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.

(ii) What is the formula of the functional group in carboxylic acids?
A
–OH
B
–CH₃
C
–COOH
D
–CO₂

Ethanol can be used as a liquid fuel - Edexcel - GCSE Chemistry - Question 4 - 2018 - Paper 1

Worked Solution & Example Answer:Ethanol can be used as a liquid fuel - Edexcel - GCSE Chemistry - Question 4 - 2018 - Paper 1

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

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

Calculate the amount of heat energy used.

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

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

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

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