This question is about the halogens - AQA - GCSE Chemistry - Question 8 - 2020 - Paper 1
Question 8
This question is about the halogens.
Table 5 shows the melting points and boiling points of some halogens.
Table 5
Element Melting point in °C Boiling point in °C... show full transcript
Worked Solution & Example Answer:This question is about the halogens - AQA - GCSE Chemistry - Question 8 - 2020 - Paper 1
Step 1
What is the state of bromine at 0 °C and at 100 °C?
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Answer
At 0 °C, bromine is in a liquid state as its melting point is -7 °C. At 100 °C, bromine is in a gaseous state since its boiling point is 59 °C.
Step 2
Explain the trend in boiling points of the halogens shown in Table 5.
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Answer
The boiling point of halogens increases down the group due to the increase in relative formula mass and size of the molecules. As the molecules get larger, the intermolecular forces between them become stronger, requiring more energy to separate the molecules during the phase change from liquid to gas.
Step 3
Why is it not correct to say that the boiling point of a single bromine molecule is 59 °C?
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The boiling point is a bulk property that applies to a substance in large amounts. It refers to the temperature at which a considerable number of molecules transition from liquid to gas, rather than an isolated molecule.
Step 4
Give one reason why this experiment should be done in a fume cupboard.
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Answer
The gas / halogen is toxic, hence the experiment should be conducted in a fume cupboard to prevent inhalation of harmful gases.
Step 5
Explain why the reactivity of the halogens decreases going down the group.
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Answer
As we move down the group, the outer electrons become further from the nucleus due to increased atomic radius. Consequently, there is less attraction between the nucleus and the outer electrons, making it harder for the halogens to gain an electron.
Step 6
Calculate the simplest whole number ratio of moles of iron atoms : moles of chlorine atoms.
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Answer
To calculate moles:
Moles of iron:
extMolesofFe=56extg/mol4.48extg=0.08
Moles of chlorine:
extMolesofCl=35.5extg/mol8.52extg=0.24
Therefore, the ratio of Fe to Cl is:
0.240.08=1:3.
Step 7
Determine the balanced equation for the reaction.
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Answer
The balanced equation for the reaction of iron with chlorine is:
ext2Fe+ext3Cl2→2 FeCl3.
