The table and Fig. 1 show trials at a recycling facility that changes long-chain hydrocarbons from used lubricating oil into smaller molecules. Oil is heate...
Question 1 Report
The table and Fig. 1 show trials at a recycling facility that changes long-chain hydrocarbons from used lubricating oil into smaller molecules. Oil is heated until it forms a gas, then passed through a reactor containing hot aluminium oxide catalyst. The products enter a cold trap. The liquid collected is tested separately from the gas leaving the trap. Ethene is wanted because it can be used to make polymers. The reaction does not involve acid, sodium chloride solution or water.
Table 1 gives the masses obtained from equal masses of oil.
| Catalyst temperature / degrees C | Mass of ethene collected / g | Mass of liquid product / g |
|---|---|---|
| 450 | 8.0 | 71.5 |
| 550 | 14.0 | 65.0 |
(a) State what happens to the long-chain hydrocarbon molecules in the reactor. [2]
(b) Complete the equation for one possible cracking reaction.
C16H34 → C2H4 + ................. [2]
(c) Explain why the oil is vaporised before it reaches the catalyst pellets. [2]
(d) Calculate the increase in mass of ethene when the temperature is changed from 450 degrees C to 550 degrees C. [2]
(e) Give a chemical test for ethene in the gas leaving the cold trap, including the positive result. [2]
Answer Details
(a) In cracking, large hydrocarbon molecules are broken into smaller molecules. The products include smaller alkanes and alkenes such as ethene. [2]
(b) Balance the atoms:
\[\mathrm{C_{16}H_{34}\rightarrow C_2H_4+C_{14}H_{30}}\]
The missing product is C14H30. [2]
(c) The oil is vaporised so it can flow or pass over the catalyst. Gas particles contact the catalyst surface more effectively, increasing the rate at which cracking can occur. [2]
(d) \[14.0-8.0=6.0\text{ g}\]
The ethene mass increases by 6.0 g. [2]
(e) Bubble the gas through bromine water. A positive result for ethene is that bromine water changes from orange or brown to colourless. [2]
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