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2025 H2 Chem P2 Q6: Biodiesel & Esters Solution

Biodiesel & Esters 2025 A-Level H2 Chemistry · Paper 2 · Q6 · 8 marks

Question

Diesel contains a mixture of hydrocarbons that each contain between 15 and 25 carbon atoms.

Biodiesel can be used as a fuel in diesel engines instead of using diesel produced from crude oil. Biodiesel is produced from vegetable oils which are extracted from plants.

There are many advantages to using biodiesel instead of diesel produced from crude oil as a fuel, including:
• biodiesel is a renewable resource
• a reduction in unburned fuel emissions
• a reduction in solid carbon emissions
• a reduction in CO emissions
• negligible \(SO_2\) emissions.

To produce biodiesel, the vegetable oil is converted into methyl esters. Table 6.1 shows information on the complete combustion of four hydrocarbons that can be found in diesel produced from crude oil and three methyl esters found in biodiesel.

Figure table_6_1

(a)(i)[1]

The methyl ester made from pentadecanoic acid and methanol is called methyl pentadecanoate.

Use the information in Table 6.1 to suggest the name for methyl ester L.

(a)(ii)[1]

Draw the structure of methyl ester N.

(b)[2]

Use information from Table 6.1 to explain why using biodiesel in diesel engines reduces the amount of unburned fuel, carbon monoxide gas and solid carbon emissions in the exhaust gases.

(c)[1]

Using information from Table 6.1, suggest one disadvantage of using biodiesel instead of diesel as a fuel.

(d)[2]

Predict the effect, if any, on the amount of unburned fuel, carbon monoxide gas and solid carbon emissions with methyl esters that contain at least one carbon-carbon double bond compared to methyl esters with no carbon-carbon double bonds. Use data from Table 6.1 to support your answer.

(e)[1]

Suggest why scientists do not describe the release of carbon dioxide into the atmosphere when biodiesel is burned as contributing to the enhanced greenhouse effect.

Video Solution

Overview

Question 6 links esters to biodiesel. Using a data table, you name one methyl ester and draw the structure of another, then explain why biodiesel produces less unburned fuel, less carbon monoxide and less solid carbon than ordinary diesel. You suggest one disadvantage of biodiesel, predict how carbon-carbon double bonds in the ester chains affect these emissions, and explain why the carbon dioxide released when biodiesel burns is not counted towards the enhanced greenhouse effect. It rewards clear reasoning from the data rather than recall.

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