Group 7 (17), the Halogens (AQA A Level Chemistry)

A group of students is discussing the properties of Group 7 elements and their compounds.

Student A states that astatine would have a higher boiling point than iodine, but student B disagrees. Student B states that fluorine would have the highest boiling point of the elements in Group 7. 

State whether Student A, Student B or neither of the students is correct. Explain your answer. 

The students also discussed the reactions and uses of elements of Group 7. Chlorine is added to drinking water to ensure that it is safe to drink. 

State a concern with adding chlorine to drinking water and write an equation for the reaction of chlorine with cold water.

Chlorine will also react with cold, dilute sodium hydroxide. 

Write the equation for this reaction.

The students had to plan a method that they could use, to determine the trend in reactivity down Group 7 using displacement reactions. In their plan, they had to use potassium chloride solution, potassium bromide solution and potassium iodide solution, as well as aqueous samples of each of the halogens. 

Describe how the students would use the reagents named above to determine the trend in reactivity down Group 7 and suggest the trend that the students would find from their results.

Explain your answer, using relevant ionic equations. 

Chlorine, iodine monochloride and sodium chloride all contain chlorine atoms.

Predict the order of the melting points for each of the compounds named above.

Justify your predictions.

The halides act as reducing agents in certain reactions. 

When chlorine and bromide ions react together, the bromide ions act as reducing agents.

Deduce the half equation to demonstrate the bromide ions acting as reducing agents and explain why they are stronger reducing agents than chloride ions.

Halide ions are formed when the halogens gain electrons. When the halogens react with sodium, they produce sodium halides. 

The sodium halides will react with concentrated sulfuric acid, to produce a variety of products. 

State the role of the sulfuric acid when it is reacted with solid sodium chloride.

State an observation that would be made when concentrated sulfuric acid is reacted with solid sodium chloride. 

State one additional observation which would be made from a further reaction between concentrated sulfuric acid and solid sodium iodide, and name the product responsible for this observation.

This question is about the reactions and properties of the elements in Group 7 of the Periodic Table. 

Define the term electronegativity and explain the trend in electronegativity seen down Group 7.

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

Write relevant equations to justify your answer.

Explain why bromine is a liquid at room temperature, but fluorine and chlorine are gases. 

Chlorine is used to treat water to make sure that it is safe to use. When water is exposed to direct sunlight, the chlorine present in the water can react and be lost from the water. 

Write an equation for the reaction that occurs between chlorine and water in direct sunlight. 

Chlorine will react with cold, dilute sodium hydroxide.

i) Write the equation for this reaction and give an important use of the solution which is formed.

ii) State the IUPAC name of the product formed which contains both chlorine and oxygen, and explain why this reaction is an example of a disproportionation reaction.

There are many compounds which contain the chloride ion, Cl^-.

State a simple test tube reaction you could do to determine whether chloride ions were present in an unknown solution.

Write the simplest ionic equation, with state symbols, in your answer. 

Nitric acid must be used before the key reagent is added in the test tube reaction in part (b).

i) State why it is necessary to use nitric acid in this test.

ii) Explain how ammonia can be used as a further test to distinguish between the presence of different halide ions and state why this test might be necessary.

Sodium iodide is an example of a sodium halide, which will react with concentrated sulfuric acid in a redox reaction.

Name a solid sodium halide which will not undergo a redox reaction with concentrated sulfuric acid.

A group of students were completing test tube reactions to identify three samples, X, Y and Z, since their labels had fallen off the bottles. All of the samples were solutions of sodium salts.

The positive results of the tests are shown in Table 1 below.

Table 1

Using the results from Table 1, identify X, Y and Z and write ionic equations, including state symbols, to demonstrate the key reactions taking place in each of the test tube reactions.

C₃H₇Cl, C₃H₇Br and C₃H₇I will all react in the same way when water, ethanol and aqueous sodium hydroxide are added and the reaction mixture is gently warmed. During these hydrolysis reactions, acidified silver nitrate solution can also be added, which  results in a precipitate being formed.

State and explain which of the three halogenoalkanes will react the most rapidly, producing the precipitate the fastest.

A solid sample of compound Z from part (a), will react with concentrated sulfuric acid.

Write equations, including state symbols, for all reactions which occur.

State one observation that could be made. 

Two students are debating the oxidising ability of Group 7.

Student A states that the oxidising ability of the halides increases down the group, but Student B states that it is the oxidising ability of the halogen molecules that increases down the group.

Justify whether Student A, Student B or neither student is correct. 

Aqueous samples of potassium chloride, potassium bromide, and potassium sulfate were accidentally mixed up in a laboratory.

Explain what chemical tests a student could perform to successfully identify each compound in the test tubes.

Write ionic equations, with state symbols, for any reactions that may take place.

A student reacted solid potassium bromide with concentrated sulfuric acid.

i) Write half equations for the conversion of H₂SO₄ to S and Br^- to Br₂.

ii) Write the full equation from the half equations outlined in part (b) (i).

An acid base reaction occurs for the reaction between solid potassium bromide and concentrated sulfuric acid. The equation for this is:

2H₂SO₄ (aq) + 2KBr (s) → K₂SO₄ (aq) + SO₂ (g) + Br₂ (g) + 2H₂O (l)

In this reaction redox products are also formed. List all of the redox products produced from the reaction between solid potassium bromide and concentrated sulfuric acid and give observations for any products.

Explain why the reaction between solid potassium iodide and concentrated sulfuric acid produces hydrogen sulfide whereas the reaction between solid potassium bromide, and concentrated sulfuric acid does not.

Chlorine is added to swimming pools in controlled amounts to kill any bacteria that may cause illness to those using the pool.

If chlorine reacts with water in the absence of sunlight an equilibrium is established.

i) Write an equation for the reaction that occurs.

ii) State the name of the type of reaction that is taking place and explain your answer using oxidation numbers.

A student states that in the reaction in part (a) chlorine oxidises the water.

Justify whether the student is correct.

The uric acid in urine can react with one of the products in the reaction in part (a) producing a toxic compound known as cyanogen chloride.

Explain why this should not be a concern for the swimming pool users.

When aqueous chlorine is added to cold, aqueous sodium hydroxide to produce a key ingredient to produce bleach.

i) Give the ionic equation for this reaction.

ii) Explain why it is important not to add any household cleaning agents that contain hydrochloric acid to a solution of bleach.

Sodium bromate, NaBrO₃, is a compound that is mainly used in batch and continuous dyeing processes.

i) The bromate ion, BrO₃^-, contains two Br=O double bonds and one Br-O single bond. Draw the Lewis structure of the bromate ion.

ii) Write the half equation for the production of BrO^- from BrO₃^- ion.

The hypobromite ion, BrO^-, and oxygen can be formed directly in drinking water via the ozonation of bromide ions which are already present. The hypobromite formed can then react further with ozone, O₃ to produce the bromate ion, BrO₃^-.

Write the equation for both of these processes, state symbols are not required.

Bromate ions are toxic and fish eggs exposed to bromate can develop disorders in the brain and spine. This can also poison humans, where symptoms include acute gastrointestinal irritation and depression of the central nervous system.

Another reaction in which bromate ions are formed is by the reaction with disinfection contaminants, such as hypochlorite, HClO, in sea water shown in the equation.

Br^- + 3HClO + 3OH- → BrO₃^- + 3Cl^- + 3H₂O

State the oxidation number for Cl in HClO and Cl^-.

Identify the oxidising agent in this reaction for the reaction given in part (c). Justify your answer.

The structure for a tertiary halogenoalkane is shown in Figure 1. X can represent either a fluorine, chlorine, bromine or iodine atom.

Figure 1

With reference to bond enthalpy explain why the reaction with aqueous potassium hydroxide, KOH (aq), to produce a tertiary alcohol when X = F is the slowest.

Suggest a method to show how the rate of reaction is different for each molecule drawn in Figure 2 when they are reacted independently with aqueous potassium hydroxide.

Figure 2

Hydrogen halides, H-X, are formed from the reaction of hydrogen and a halogen, X₂. In solution hydrogen fluoride is classed as a weak acid, whereas HCl is classed as a strong acid.

Explain this difference.

Suggest a method different to your answer in part (b) that would enable a student to identify a hydrogen halide, H-X, when X could be Cl, Br or I.

Give one observation and one equation, including state symbols, for the reaction that will occur with one of the hydrogen halide compounds. 

Lead dioxide reacts with hydrogen chloride to give lead chloride, chlorine and water.

i) Write the overall equation for this reaction.

ii) By using oxidation numbers explain which compound is the oxidising agent and which compound is the reducing agent.

Table 1 shows the boiling points of some halogenoalkanes.

Table 1

A student states that the boiling point increases due to the strength of the C-X bond in the molecule increasing down group 7.

State whether the student is correct and justify your answer.

The halogens can react with iron wool to produce various iron compounds including iron (III) chloride, iron (III) bromide and iron (II) iodide. The Fe²⁺ ion can also react with chlorine, Cl₂ and bromine, Br₂.

i) State the half equation for the conversion of Br₂ to Br^-

ii) State the half equation for the conversion of Fe²⁺ to Fe³⁺

iii) Hence, give the full equation for the reaction of Br₂ and Fe²⁺

iv) Explain why I₂ cannot convert Fe²⁺ to Fe³⁺ 

v) State an alternative equation involving Fe²⁺ and Fe³⁺ ions that justifies your answer to part (iv).

Chlorine gas can be reacted with solid iodine to produce iodine monochloride, ICl, which is a brown liquid at room temperature.

i) Give the equation for this reaction.

ii) Iodine monochloride, ICl, can be reacted further with chlorine to establish an equilibrium producing ICl₃  as the only product.

ICl (l) + Cl₂ (g) ⇌ ICl₃ (s)
dark brown  yellow

ICl is placed in a U tube and chlorine gas is passed over it. Suggest one observation if the chlorine supply was increased and justify your answer.