4.1 Which compound in the table is a gas at room temperature?
4.2 Define the term homologous series - NSC Physical Sciences - Question 4 - 2016 - Paper 2
Question 4
4.1 Which compound in the table is a gas at room temperature?
4.2 Define the term homologous series.
4.3 A type of van der Waals force exists between molecules of ... show full transcript
Worked Solution & Example Answer:4.1 Which compound in the table is a gas at room temperature?
4.2 Define the term homologous series - NSC Physical Sciences - Question 4 - 2016 - Paper 2
Step 1
Which compound in the table is a gas at room temperature?
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Answer
The compound that is a gas at room temperature is Butane (Compound A) with a boiling point of -1 °C.
Step 2
Define the term homologous series.
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Answer
A homologous series is a group of organic compounds that have the same functional group, with each member differing from the next by a -CH₂- group.
Step 3
A type of van der Waals force exists between molecules of compound A and also between molecules of compounds B, C, D and E. Write down the NAME of the Van der Waals force.
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Answer
The NAME of the Van der Waals force is London dispersion forces.
Step 4
Refer to the TYPE and STRENGTH of intermolecular forces to explain the difference in the boiling points between: Compounds A and B
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Answer
Compounds A (Butane) and B (Butane-2-one) have different boiling points due to the types of intermolecular forces present. Butane experiences weaker London dispersion forces, whereas Butane-2-one has stronger dipole-dipole interactions due to its polar carbonyl functional group, resulting in a higher boiling point for Butane-2-one.
Step 5
Refer to the TYPE and STRENGTH of intermolecular forces to explain the difference in the boiling points between: Compounds C and D
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Answer
Compounds C (Butanol-1) and D (Butanoic acid) show a significant difference in boiling points due to hydrogen bonding. Butanol-1 has hydrogen bonding, but Butanoic acid has stronger hydrogen bonding because it has both polar OH and carbonyl groups, leading to a much higher boiling point for Butanoic acid.
Step 6
Which compound has a HIGHER vapour pressure?
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Answer
Compounds D (Butanoic acid) and E (Pentanonic acid) can be compared, where Butanoic acid generally has a higher vapour pressure due to its lower boiling point relative to Pentanonic acid.
Step 7
Refer to MOLECULAR STRUCTURE, TYPE and STRENGTH of INTERMOLECULAR FORCES to explain the answer to QUESTION 4.5.1.
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Answer
Butanoic acid has a lower boiling point compared to Pentanonic acid despite having hydrogen bonding due to the differences in molecular weight and size. While both have hydrogen bonding, the larger chain of Pentanonic acid leads to a higher boiling point and lower vapour pressure overall.
