Intermolecular forces: Grade 11 Past Paper Questions

QUESTION 4. 4.1 In an experiment to investigate the relationship between the hydrides of group IV and their boiling points, the following results were obtained: CH₄ (16 g·mol⁻¹, −161 °C), SiH₄ (32 g·mol⁻¹, −112 °C), GeH₄ (77 g·mol⁻¹, −49 °C), SnH₄ (123 g·mol⁻¹, −52 °C). 4.1.1 Define the term boiling point. 4.1.2 Identify the independent variable in this experiment. 4.1.3 Use a relevant calculation to determine whether the bond between silicon (Si) and hydrogen is POLAR or NON-POLAR. 4.1.4 Which one of the above hydrides will be a liquid at −60 °C? 4.1.5 Which one of the above hydrides will have the greatest vapour pressure at −180 °C? 4.1.6 Fully explain why SiH₄ has a higher boiling point than CH₄. 4.2 The graph below shows the relationship between the boiling points of the hydrides of a certain group of the periodic table, and their relative molecular masses. W, X, Y and Z are elements in this group. Boiling points were measured at atmospheric pressure of one atmosphere. 4.2.1 State the relationship between boiling point and molecular mass for H₂X, H₂Y and H₂Z. 4.2.2 Explain the relationship referred to in QUESTION 4.2.1. 4.2.3 Identify element W. Give a reason for the answer. 4.2.4 Explain why H₂W has a much higher boiling point than expected.

QUESTION 5. 5.1 Define solubility. 5.2 Will iodine, I₂(s), dissolve in water, H₂O(l)? Explain, referring to the polarity of the molecules and the types of intermolecular forces involved.

QUESTION 1: MULTIPLE-CHOICE QUESTIONS. 1.1 The hydrogen bond is a type of... A. ionic bond. B. metallic bond. C. covalent bond. D. intermolecular force. 1.2 Which ONE of the following substances has dative covalent bonds? C. H₃O⁺ D. NH₄⁺. 1.3 Which ONE of the following liquids will have the greatest vapour pressure when equal amounts are placed in a sealed container at the same temperature? A. HF B. HCl C. HBr D. HI. 1.4 Which ONE of the following statements is correct about intermolecular forces? A. They hold atoms together in a molecule. B. They are much stronger than intramolecular forces. C. They determine the physical state of the compound. D. They are chemical bonds.

4.2.3 Identify element W. Give a reason for the answer. 4.2.4 Explain why H₂W has a much higher boiling point than expected. QUESTION 5. 5.1 Define solubility. 5.2 Will iodine, I₂(s), dissolve in water, H₂O(l)? Explain, referring to the polarity of the molecules and the types of intermolecular forces involved.

A multiple-choice section (5 items). Then in Question 2: define a covalent bond, a molecule, and a lone pair; state the number of lone pairs and bonds shown in given structures; identify the type of bond (covalent) in given structures; name two molecules that contain lone pairs (H₂O and NH₃); and use dative covalent bonding to explain how the hydronium ion (H₃O⁺) and the ammonium ion (NH₄⁺) form.

Continuing Question 4: compare the boiling points of methane (CH₄) and methanol (CH₃OH), and of water (H₂O) and methanol, in terms of their intermolecular forces and number of hydrogen-bonding sites; identify which of the group has the lowest boiling point (methane). Then Question 5: define solubility, and explain why iodine dissolves in carbon tetrachloride but not in water, in terms of the strength of the intermolecular forces involved (London forces between non-polar molecules versus water's hydrogen bonds).