A refrigerant is a chemical used in cooling processes - Scottish Highers Chemistry - Question 10 - 2023
Question 10
A refrigerant is a chemical used in cooling processes. Some refrigerant compounds can damage the ozone layer.
(a) The ozone depletion potential (ODP) of a refrigera... show full transcript
Worked Solution & Example Answer:A refrigerant is a chemical used in cooling processes - Scottish Highers Chemistry - Question 10 - 2023
Step 1
Describe a relationship between the formulae of refrigerant compounds 3, 4 and 5 and their ODP.
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Answer
Refrigerant compounds 3 (C2FCl5), 4 (C2F3Cl), and 5 (C2F2Cl2) show a relationship where increasing chlorine atoms lead to a decrease in the ozone depletion potential (ODP). Specifically, compound 3, having five chlorine atoms, has a higher ODP, while compound 5, with two chlorine atoms, shows a significantly lower ODP. Thus, less fluorine or more chlorine results in a higher ODP.
Step 2
Identify which pair of compounds should be used to show the effect of replacing chlorine atoms with bromine atoms in refrigerant compounds.
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Compound 2 (CF2ClBr) and compound 1 (C2F4Br2) should be compared to show the effect, as both contain bromine where chlorine is replaced.
Step 3
Suggest why carbon dioxide and ammonia have ODP values of 0.00.
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Answer
Carbon dioxide (CO2) and ammonia (NH3) do not deplete the ozone layer because they do not contain chlorine or bromine atoms, which are primarily responsible for ozone layer depletion. Therefore, their ODP values remain at 0.00.
Step 4
State what is meant by a free radical.
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Answer
A free radical is a species that has one or more unpaired electrons, making it highly reactive.
Step 5
State the name given to the step of splitting a fluorine molecule to produce two fluorine radicals.
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This step is called initiation.
Step 6
Write an equation for a possible propagation step in this reaction.
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Answer
A possible propagation step is:
F• + CH3F → CHF2• + HF
Step 7
Calculate the number of moles of pentafluoroethane required to make 0.05 kg of coolant.
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Answer
Given the coolant is 50% by mass CH2F2 and 50% CF5H2:
Mass of CF5H2 = 0.25 kg = 250 g.
Using the GFM of CF5H2 (120 g/mol):
Number of moles of CF5H2 = (\frac{250 g}{120 g/mol} = 2.0833 \text{ moles} \approx 2.08 \text{ moles}).
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