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e) Two gases, X and Y, react to give a gaseous product Z - Edexcel - GCSE Chemistry Combined Science - Question 9 - 2016 - Paper 1
Question 9
e) Two gases, X and Y, react to give a gaseous product Z. The reaction is carried out under two different sets of conditions in experiments 1 and 2 as shown in Figur... show full transcript
Worked Solution & Example Answer:e) Two gases, X and Y, react to give a gaseous product Z - Edexcel - GCSE Chemistry Combined Science - Question 9 - 2016 - Paper 1
Step 1
Explain why it is not possible to predict the rate of Experiment 2 compared with Experiment 1
Answer
To predict the appearance of astatine, which is directly below iodine in group 7, we can infer based on the trend of halogens. As we move down the group from chlorine to iodine, the state of the element changes from gas to liquid to solid. Therefore, we can predict that astatine will exhibit characteristics of a solid at room temperature. Additionally, its color is likely to follow a pattern of darkening, being a dark, possibly black or metallic solid.
Step 2
Explain how displacement reactions can be used to show the reactivity of chlorine, bromine, and iodine
Answer
Displacement reactions are a useful method for determining the reactivity of halogens. The reactivity of halogens decreases as you move down the group from chlorine to iodine. Here’s how displacement reactions can demonstrate this:
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Reactivity Comparison: In a displacement reaction, a more reactive halogen can displace a less reactive halogen from its compound. For example, when chlorine (the most reactive) is added to a solution of potassium bromide (which contains bromine), chlorine will displace bromine, forming potassium chloride and releasing bromine:
ext{Cl}_2 + ext{2KBr} ightarrow ext{2KCl} + ext{Br}_2
This indicates that chlorine is more reactive than bromine.
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Further Reactions: Similarly, if bromine is placed in a solution of potassium iodide, it will displace iodine, demonstrating that bromine is more reactive than iodine:
ext{Br}_2 + ext{2KI} ightarrow ext{2KBr} + ext{I}_2
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Lack of Reaction: If iodine is mixed with potassium chloride or potassium bromide, no reaction occurs, confirming its lower reactivity.
In summary, the use of displacement reactions provides direct evidence of the reactivity series of halogens, as more reactive elements will replace less reactive ones in compound formation.