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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 | Boili... 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?
Answer
At 0 °C, bromine is a liquid because its melting point is -7 °C, which indicates that it is in the liquid state above its melting point. At 100 °C, bromine is a gas because its boiling point is 59 °C, meaning that it will be in a gaseous state above this temperature.
Step 2
Explain the trend in boiling points of the halogens shown in Table 5.
Answer
The boiling points of the halogens increase down the group. This can be attributed to two main factors: the increase in relative molecular mass and the increase in the size of the molecules. As the size of the halogen molecules increases, the intermolecular forces between the molecules also increase, requiring more energy to overcome these forces. Therefore, the boiling points of the halogens rise as you move from fluorine to bromine.
Step 3
Why is it not correct to say that the boiling point of a single bromine molecule is 59 °C?
Answer
The boiling point is a bulk property, which means it refers to the phase change of a substance in large quantities rather than for a single molecule. Hence, the boiling point of 59 °C refers to a bulk sample of bromine, where multiple molecules are involved in the phase transition.
Step 4
Give one reason why this experiment should be done in a fume cupboard.
Answer
One reason this experiment should be conducted in a fume cupboard is that the gas or halogen used is toxic. Using a fume cupboard helps prevent inhalation of harmful gases and ensures a safer working environment.
Step 5
Explain why the reactivity of the halogens decreases going down the group.
Answer
The reactivity of halogens decreases down the group because, as you go down, the outer electrons are located in shells that are further from the nucleus. This distance reduces the nucleus's attraction to the incoming electron, making it less likely to gain an electron. Additionally, increased shielding from inner electron shells decreases the effective nuclear charge felt by the outer electrons, further diminishing reactivity.
Step 6
Calculate the simplest whole number ratio of moles of iron atoms : moles of chlorine atoms.
Answer
To calculate the moles of iron (Fe) and chlorine (Cl) used in the reaction:
- Moles of iron = mass of iron / atomic mass of iron = 4.48 g / 56 g/mol = 0.08 moles
- Moles of chlorine = mass of chlorine / atomic mass of chlorine = 8.52 g / 35.5 g/mol = 0.24 moles
The simplest whole number ratio of moles of iron to moles of chlorine:
Ratio = (0.08:0.24) = 1:3.
Thus, the simplest ratio is 1 mole of iron to 3 moles of chlorine.
Step 7
Determine the balanced equation for the reaction.
Answer
Based on the mole ratio calculated, the balanced equation for the reaction between iron and chlorine is:
2 Fe + 3 Cl₂ → 2 FeCl₃.
This indicates that 2 moles of iron react with 3 moles of chlorine gas to produce 2 moles of iron(III) chloride.