Question 3

3.1 The boiling points in the table below were obtained during an investigation carried out to compare the boiling points of group 7 hydrides. The hydrides, HCℓ and HBr, are labelled in the table as compounds A and B respectively.

3.1.1 Define the term boiling point. (2)

3.1.2 In what phase are compounds (A and B) at 0 °C and 101 kPa of external pressure? (1)

3.1.3 Name the type of intermolecular force that exists between molecules of both compounds A and B due to the polar nature of these molecules. (1)

3.1.4 Which ONE of the compounds (A or B), has STRONGER London forces (dispersion forces)?

Give a reason for your answer. (3)

3.1.5 Which compound (A or B), will have the higher vapour pressure?

Give a reason for the answer by referring to the data in the table. (2)

Compound C (HF), not shown in the table, has a smaller molecular size
than both compounds A and B but has a relatively higher boiling point of
19,5 °C.

3.1.6 Explain why the boiling point of compound C is HIGHER than that of compounds A and B by referring to the TYPE and STRENGTH of intermolecular forces involved. (3)

3.2 Solid iodine (I2) is added to equal volumes of carbon tetrachloride (CCℓ4) and water in separate test tubes as shown in the diagram below.

3.2.1 In which liquid (CCℓ4 or H2O), will the iodine dissolve? (1)

3.2.2 Explain the answer to QUESTION 3.2.1 above by referring to the intermolecular forces involved. (3)


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