Propenes can be produced by the cracking of some hydrocarbons obtained from crude oil - Edexcel - GCSE Chemistry - Question 5 - 2019 - Paper 1
Question 5
Propenes can be produced by the cracking of some hydrocarbons obtained from crude oil. The equation shows the cracking of one molecule of decane to produce one molec... show full transcript
Worked Solution & Example Answer:Propenes can be produced by the cracking of some hydrocarbons obtained from crude oil - Edexcel - GCSE Chemistry - Question 5 - 2019 - Paper 1
Step 1
(a)(i) Calculate the values of x and y in C₇H₈.
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Answer
In the hydrocarbon formula C₇H₈, there are 7 carbon atoms and 8 hydrogen atoms. Therefore, the values are:
x = 6
y = 14
Step 2
(a)(ii) State the total mass of products formed if 25 g of decane is cracked in this way.
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The total mass of products formed from the cracking of decane can be found using the concept of conservation of mass. Since the equation shows a molecular rearrangement without any loss of mass:
The mass of decane before cracking is 25 g. Therefore, the total mass of products formed will also be 25 g.
Step 3
(b)(i) Complete Figure 9 to show the electrons of the C=C double bond.
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To complete Figure 9, place 4 electrons (2 pairs) between the carbon atoms of the C=C double bond. This can be represented as pairs of dots or crosses as shown in typical dot-and-cross diagrams.
Step 4
(b)(ii) The incomplete combustion of ethene in air produces water as one of the products. Give the name of another product of the incomplete combustion of ethene.
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Another product of the incomplete combustion of ethene is carbon monoxide (CO).
Step 5
(c) Explain how the structure of substance X shows that it is an unsaturated hydrocarbon.
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Substance X is classified as an unsaturated hydrocarbon because it contains at least one carbon-carbon double bond (C=C) in its structure, which is characteristic of unsaturated compounds. This allows for the possibility of additional hydrogen atoms being added to the compound.
Step 6
(d) Explain these results.
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The results indicate that hydrocarbon A, known to be an alkane, reacts with bromine water to decolorize it, demonstrating that it is saturated and does not contain double or triple bonds. In contrast, hydrocarbon B, an alkene, does not decolorize the bromine water, indicating that it has unsaturated bonds, which are less reactive compared to alkenes.
