The Chemical Properties of the Halogen Elements & the Hydrogen Halides (Cambridge (CIE) A Level Chemistry)

A group of students are asked to determine the order of reactivity of the halogens and are provided with solutions of potassium chloride, potassium bromide and potassium iodide, as well as aqueous samples of each of the halogens. 

i) Describe how the students would use the reagents named above to determine the trend in reactivity down Group 17 and give expected observations.

ii) Suggest the trend that the students would find from their results.

iii) Explain your answer to part (a)(ii), using relevant ionic equations. 

Suggest one extra reagent the students could use to make their observations more clear.

Halogens react with hydrogen gas to form hydrogen halides. Chlorine reacts with hydrogen when exposed to ultraviolet light to form hydrogen chloride.

i) Write an equation for the reaction of chlorine and hydrogen.

[1]

ii) Explain why the thermal stability of the hydrogen halides decreases down the group.

[3]

The hydrogen halides do not show perfect periodicity. A bar chart of boiling points, as seen in Fig. 2.1, shows that the boiling point of hydrogen fluoride, HF, is much higher than periodic trends would indicate.

Fig. 2.1 

Explain why the boiling point of HF is much higher than the boiling point of the other hydrogen halides.

There is an increase in boiling point moving from HCl to HI.

Explain this trend in boiling points of the hydrogen halides.

Explain why HF is more thermally stable than HI.

This question is about the reactions and properties of the elements in Group 17 of the Periodic Table. 

Define the term electronegativity and explain the trend in electronegativity seen down Group 17.

definition

explanation

Describe how an aqueous of solution of a halogen could be used to successfully distinguish between solutions containing potassium chloride, potassium bromide and potassium iodide. 

Provide relevant equations to justify your answer.

Bromine is used to extract iodine from a solution containing iodide ions.

Explain why iodine is a weaker oxidising agent than than bromine.