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Three compounds are used to investigate one of the factors that influences boiling point - NSC Physical Sciences - Question 3 - 2019 - Paper 2
Question 3
Three compounds are used to investigate one of the factors that influences boiling point. The results obtained are shown in the table below. COMPOUND MOLECULAR MASS... show full transcript
Worked Solution & Example Answer:Three compounds are used to investigate one of the factors that influences boiling point - NSC Physical Sciences - Question 3 - 2019 - Paper 2
Step 1
Is this a fair investigation? Write down YES or NO. Refer to the data in the table and give a reason for the answer.
Answer
NO, this is not a fair investigation because the two compounds being compared (Propan-1-ol and Ethanoic acid) have different molecular masses and structures, which affect their boiling points differently. This makes it difficult to accurately compare boiling points based solely on the compounds' identities.
Step 2
Step 3
Which ONE of the compounds (A, B or C) has the highest vapor pressure? Give a reason for the answer.
Answer
Compound A (Butane) has the highest vapor pressure. This is because Butane has weaker London dispersion forces compared to the hydrogen bonding present in Propan-1-ol and Ethanoic acid, allowing it to vaporize more easily.
Step 4
Refer to the intermolecular forces present in each compound and FULLY explain the trend in boiling points, as shown in the table above.
Answer
The boiling points of the compounds can be explained by analyzing their intermolecular forces:
- Compound A (Butane) has London dispersion forces, which are relatively weak. This results in a lower boiling point compared to the others.
- Compound B (Propan-1-ol) has hydrogen bonds due to the presence of an -OH group, which are stronger than London dispersion forces. Thus, Propan-1-ol has a higher boiling point than Butane.
- Compound C (Ethanoic acid) has two -OH groups allowing for stronger hydrogen bonding. This leads to an even higher boiling point due to the significant energy required to overcome these intermolecular forces.
Overall, the trend shows that as the strength of intermolecular forces increases, the boiling point also rises.
Step 5
Which compound, BUTAN-1-OL or PROPAN-1-OL, has the higher boiling point? Give a reason for the answer.
Answer
BUTAN-1-OL has the higher boiling point than PROPAN-1-OL. This is due to its larger molecular size leading to stronger intermolecular forces. The larger chain length results in increased surface area for London dispersion forces, contributing to its higher boiling point.