Senior Secondary (HKDSE) · Chemistry

Intermolecular forces: Van der Waals’, hydrogen bonds: Practice Questions

5 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on Intermolecular forces: Van der Waals’, hydrogen bonds.

10 questions19 marksFree, no account

Question 1

1 mark

Which of the following substances is expected to have the strongest intermolecular hydrogen bonds between its own molecules?

Question 2

1 mark

Consider the boiling points of fluoromethane ($CH_3F$) and methanol ($CH_3OH$). The boiling point of fluoromethane is $-78.4^ C$, while that of methanol is $64.7^ C$. Both molecules have similar molar masses.

Which of the following statements best explains the significant difference in their boiling points?

Question 3

1 mark

Catechol (benzene-1,2-diol) and hydroquinone (benzene-1,4-diol) are isomers with the molecular formula $C_6H_6O_2$. Catechol has a boiling point of $245^\circ C$, whereas hydroquinone has a boiling point of $287^\circ C$. Both compounds are capable of forming hydrogen bonds. Which of the following statements provides the most comprehensive explanation for the observed difference in their boiling points?

Question 4

1 mark

Butan-1-ol (

CH₃CH₂CH₂CH₂OH

), butanal (

CH₃CH₂CH₂CHO

), and ethoxyethane (

CH₃CH₂OCH₂CH₃

) are three compounds with similar molar masses. Their boiling points are

117^ C

76^ C

, and

34^ C

respectively.

Which statement correctly explains the observed trend in boiling points?

Question 5

1 mark

Consider the compounds propan-1-ol ($CH_3CH_2CH_2OH$), propan-1-amine ($CH_3CH_2CH_2NH_2$), and butane ($CH_3CH_2CH_2CH_3$). All three compounds have similar molar masses.

Which of the following statements correctly ranks their boiling points from highest to lowest and provides the best explanation?

Question 6

2 marks

Identify the type of intermolecular force that must be overcome when dry ice (solid $CO_2$) undergoes sublimation.

Write your answer out first, then check it against the worked solution.

Question 7

2 marks

State the two primary factors that determine the strength of van der Waals' forces between molecules.

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Question 8

2 marks

In terms of strength, how do hydrogen bonds typically compare to van der Waals' forces and covalent bonds?

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Question 9

3 marks

Consider the three molecules: methoxymethane ($\text{CH}_3\text{OCH}_3$), ethanol ($\text{CH}_3\text{CH}_2\text{OH}$), and propane ($\text{CH}_3\text{CH}_2\text{CH}_3$). These substances have similar relative molecular masses but exhibit different boiling points.

(a) Identify the main type of intermolecular force present in a sample of liquid ethanol and liquid methoxymethane.

(b) Arrange the three substances in increasing order of their boiling points.

(c) Explain why ethanol has a significantly higher boiling point than methoxymethane, despite having the same molecular formula ($\text{C}_2\text{H}_6\text{O}$).

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Question 10

5 marks

Water ($$H_2O$$) exhibits several anomalous properties compared to other Group 16 hydrides, largely due to the presence of hydrogen bonding.

(a) Explain what hydrogen bonding is and describe the conditions required for its formation.

(b) The boiling point of water ($$100^\text{o}C$$) is significantly higher than that of hydrogen sulfide ($$H_2S$$, $$-60^\text{o}C$$), despite $$H_2S$$ having a larger molar mass. Account for this difference.

(c) Explain why ice floats on liquid water. Refer to the specific arrangement of water molecules in ice and the intermolecular forces involved.

Write your answer out first, then check it against the worked solution.

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