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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 MAS... 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. The investigation is not fair because the boiling points of the compounds being compared (Propan-1-ol and Ethanoic acid) are influenced by their different molecular masses and intermolecular forces.
Step 2
Step 3
Which ONE of the compounds (A, B or C) has the highest vapour pressure? Give a reason for the answer.
Answer
Compound A (Butane) has the highest vapour pressure. This is because Butane has weaker London dispersion forces compared to the stronger hydrogen bonds present in Propan-1-ol and Ethanoic acid.
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 trend in boiling points is influenced by the strength of intermolecular forces. Butane (Compound A) primarily exhibits weak London dispersion forces, which leads to a lower boiling point. Propan-1-ol (Compound B) has one site for hydrogen bonding, offering slightly stronger intermolecular forces, raising its boiling point compared to Butane. Ethanoic acid (Compound C) contains two sites for hydrogen bonding, resulting in much stronger intermolecular forces, thus it has the highest boiling point of the three compounds.
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 due to its larger molecular mass compared to Propan-1-ol, which results in stronger van der Waals forces and the longer chain length contributes to this effect.