QUESTION 3 [14 marks]

Question

QUESTION 3 [14 marks]
QUESTION 3.1
The boiling points of compounds A to D are given in Table 1 below.
Table 1: Boiling points of compounds A to D.
Question 3.1.1 [2 marks]
Define the term boiling point.
Question 3.1.2 [1 mark]
Calculate the molecular mass of compound D.
Question 3.1.3 [1 mark]
In what phase is compound D at 100 °C?
Question 3.1.4 [1 mark]
Name the main type of intermolecular force present in compound A.
12
Compound Molecular formula Boiling point
A C2H4
-104 °C
B C3H6
-47 °C
C C6H12 63 °C
D C8H16 121 °C
Question 3.1.5 [4 marks]
Explain why the boiling point increases from compound A to D.
Question 3.1.6 [1 mark]
How does the vapour pressure of compound B compare to the vapour pressure
of compound C? Write down only HIGHER THAN, LOWER THAN, or EQUAL TO.
QUESTION 3.2
Consider the boiling points of the compounds, given in Table 2 below.
Table 2: Boiling point of compounds A to D
Question 3.2.1 [1 mark]
Which ONE of the substances in the table above has the strongest forces
between its molecules?
Question 3.2.2 [1 mark]
Name the type of intermolecular force found between H2 molecules.
13
Compound Molecular formula Boiling point
A H2
-252,9 °C
B HCN 25.6°C
C F2
-188 °C
D Cℓ2
-34.04 °C
Question 3.2.3 [2 marks]
Cℓ2 and F2 have vastly different boiling points despite being diatomic molecules
from the same group. Write a conclusion,in terms of a relationship
(Inverse/Direct, which gives a reason for this difference).
TOTAL: 14 marks
QUESTION 4 [14 marks]
QUESTION 4.1
A Grade 11 class investigates the relationship between temperature and volume
of a fixed amount of gas. The learners take a balloon filled with gas and dunk it
into ice water, and water that has been heated. They then measure the diameter
of the balloon.
Figure 1: balloon experiment.
Question 4.1.1 [2 marks]
Write a suitable hypothesis for this investigation.
Question 4.1.2 [2 marks]
Identify the dependent and independent variables.

GPT-4o mini · Answer

### QUESTION 3 **QUESTION 3.1** **Question 3.1.1 [2 marks]** **Define the term boiling point.** The boiling point of a substance is the temperature at which its vapor pressure equals the surrounding atmospheric pressure, causing the liquid to convert to a gas (vaporization). --- **Question 3.1.2 [1 mark]** **Calculate the molecular mass of compound D.** The molecular formula for compound D is C8H16. To calculate its molecular mass: - C: 12.01 g/mol × 8 = 96.08 g/mol - H: 1.008 g/mol × 16 = 16.13 g/mol Total molecular mass = 96.08 + 16.13 = 112.21 g/mol **Answer:** 112.21 g/mol --- **Question 3.1.3 [1 mark]** **In what phase is compound D at 100 °C?** At 100 °C, compound D (with a boiling point of 121 °C) is in the **liquid** phase. --- **Question 3.1.4 [1 mark]** **Name the main type of intermolecular force present in compound A.** The main type of intermolecular force present in compound A (C2H4) is **Van der Waals forces** (or London dispersion forces), as it is a nonpolar molecule. --- **Question 3.1.5 [4 marks]** **Explain why the boiling point increases from compound A to D.** The boiling point increases from compound A to compound D due to several factors: 1. **Molecular Size:** As the molecular size increases (from A to D), the number of electrons also increases, leading to larger induced dipoles. 2. **Increased Surface Area:** Larger molecules typically have more surface area, which allows for greater Van der Waals forces (dispersion forces) between the molecules. 3. **Intermolecular Forces:** As the size of the molecules increases, the strength of the intermolecular forces (especially dispersion forces) increases, requiring more energy (higher temperature) to overcome these forces and convert the substance from liquid to gas. 4. **Type of Bonding:** Larger hydrocarbons may also experience higher boiling points due to increased van der Waals interactions. --- **Question 3.1.6 [1 mark]** **How does the vapour pressure of compound B compare to the vapour pressure of compound C?** **Answer:** LOWER THAN --- **QUESTION 3.2** **Question 3.2.1 [1 mark]** **Which ONE of the substances in the table above has the strongest forces between its molecules?** **Answer:** B (HCN) has the strongest intermolecular forces due to hydrogen bonding. --- **Question 3.2.2 [1 mark]** **Name the type of intermolecular force found between H2 molecules.** **Answer:** London dispersion forces (or Van der Waals forces). --- **Question 3.2.3 [2 marks]** **Cℓ2 and F2 have vastly different boiling points despite being diatomic molecules from the same group. Write a conclusion, in terms of a relationship (Inverse/Direct, which gives a reason for this difference).** **Conclusion:** The boiling point difference between Cl2 and F2 is a result of an **inverse relationship** between molecular size and boiling point; as the size and number of electrons in Cl2 are greater than those in F2, this results in stronger London dispersion forces in Cl2, leading to a higher boiling point despite both being diatomic molecules. --- ### QUESTION 4 **QUESTION 4.1** **Question 4.1.1 [2 marks]** **Write a suitable hypothesis for this investigation.** **Hypothesis:** If the temperature of the gas in the balloon is increased, then the volume of the gas will also increase, due to the direct relationship as described by Charles's Law. --- **Question 4.1.2 [2 marks]** **Identify the dependent and independent variables.** - **Independent variable:** Temperature of the water (and therefore the gas) - **Dependent variable:** Volume (size/diameter) of the balloon. --- This concludes the answers to the respective questions.