Intermolecular Forces, Electronegativity & Bond Properties — Structured Questions (Cambridge International AS Chemistry): Exam Questions

State the three main types of intermolecular force and place them in ascending order of strength.

Draw a diagram to show hydrogen bonding between two molecules of methanol, CH₃OH.

Your diagram should include all relevant lone pairs of electrons and dipoles.

Extract:

The three main types of intermolecular force, in ascending order of strength:

• Instantaneous dipole-induced dipole (id-id) forces / London dispersion forces, permanent dipole-permanent dipole (pd-pd) forces, and hydrogen bonding
• (In ascending order of strength) instantaneous dipole-induced dipole forces < permanent dipole-permanent dipole forces < hydrogen bonding

Methanol, CH₃OH, can be oxidised to methanal, CH₂O, and then to methanoic acid, HCOOH.

State the strongest type of intermolecular force present between:

i) Methanal molecules

ii) Methanoic acid molecules

iii) A molecule of water and a molecule of methanal

iv) A molecule of water and a molecule of methanoic acid

Methanoic acid reacts with sodium hydroxide to form sodium methanoate:

HCOOH + NaOH → HCOONa + H₂O

Explain why sodium methanoate is a solid at room temperature and methanoic acid is a liquid.

Complete the dot-and-cross diagram of methanol, CH₃OH. Show outer shell electrons only.

Ammonia, NH₃, and methane, CH₄, are simple molecules.

Complete Table 1.1 to show the dot-and-cross diagram and the shape of a molecule of each compound. Show outer shell electrons only.

Ammonia is a polar molecule whereas methane is non-polar.

i) Explain what is meant by the term bond polarity, using the N-H bond as an example.

ii) Explain why the ammonia molecule is polar.

State the strongest type of intermolecular force present in liquid ammonia.

Ammonia gas reacts with hydrogen chloride gas to form solid ammonium chloride, NH₄Cl.

State the three types of bonding present in solid ammonium chloride.

The structural formulae of water, methanol and methoxymethane, CH₃OCH₃, are given below.

i) State the number of lone pairs of electrons around the oxygen atom in a molecule of methoxymethane.

ii) Suggest a value for the C-O-C bond angle in methoxymethane.

The physical properties of covalent compounds depend on the intermolecular forces between their molecules.

Using the letters A, B, or C, state the strongest intermolecular force present in each of the following compounds.

Extract:

The structural formulae of water, methanol and methoxymethane, CH3OCH3, are given below.

Methanol and water are completely soluble in each other.

i) Name the strongest type of intermolecular force between a molecule of methanol and a molecule of water.

ii) Draw a diagram to show this intermolecular force between one molecule of methanol and one molecule of water. Include all relevant dipoles and lone pairs of electrons.

Ethoxyethane, C₂H₅OC₂H₅, and water are immiscible.

Explain why ethoxyethane does not dissolve in water.

Explain why butan-1-ol has a higher boiling point than butanal.

Ethane, C₂H₆, and disilane, Si₂H₆, are hydrides of Group 14 elements.

Explain why disilane has a higher boiling point than ethane.

Ethanol is soluble in water, whereas ethane is insoluble.

Explain this difference.

Water has a relatively high surface tension compared to most liquids.

Explain this anomalous property of water.

Ammonia, NH₃, is highly soluble in water.

Draw diagrams to show the two different ways a hydrogen bond can form between one molecule of water and one molecule of ammonia. Your diagrams should include all relevant dipoles and lone pairs of electrons.

Ammonia, NH₃, hydrogen chloride, HCl, and fluorine, F₂, all exist as gases at room temperature and pressure. The boiling point of NH₃ is −33 °C.

Predict which gas, HCl or F₂, has the lowest boiling point. Explain the relative boiling points of all three gases in terms of the intermolecular forces present.