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

Exam Questions

3 hours45 questions
1a4 marks

Give the reagents required to test for and distinguish between the halide ions.

1b2 marks

Write an equation, including state symbols, to show the reaction between silver nitrate solution, AgNO3 (aq), and sodium bromide solution, NaBr (aq).

1c4 marks

Table 1 shows some of the physical properties of the halogens.

Table 1

Halogen

Appearance at room temperature

Boiling Point (°C)

Fluorine

Pale yellow gas

-188

Chlorine

 

-35

Bromine 

Orange / brown liquid

 

Iodine

 

183

Astatine

 

337

Complete Table 1. Suggest a value for the boiling point of bromine.

1d1 mark

Place the following halogens in order of increasing bond strength.

Chlorine, Cl2, Bromine, Br2 and Iodine, I2.

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2a3 marks

The boiling points of the hydrogen halides are represented in the graph in Figure 1

Figure 1

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Explain why hydrogen fluoride has the highest boiling point out of the hydrogen halides.

2b3 marks

A compound that exhibits a high thermal stability can withstand high temperatures before breaking down.

Hydrogen iodide, HI, has a lower thermal stability than hydrogen chloride, HCl. In terms of bond length, explain why hydrogen iodide has a lower thermal stability than hydrogen chloride.

2c1 mark

Write the equation for the preparation of hydrogen chloride gas, HCl using hydrogen gas, H2 and chlorine gas, Cl2.

2d4 marks

Halogens can react with other halide salts.

i)
Write the equation, including state symbols, for the reaction between chlorine water, Cl2, and sodium iodide, NaI.

ii)
State any observations that you may see in this reaction.

iii)
State the name of this type of reaction.

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3a1 mark

The reducing power of the halide ions increases as you go down the group.

State the meaning of the term reducing agent.

3b3 marks

State why  an iodide ion, I-, is a better reducing agent than a chloride ion, Cl-.

3c3 marks

A student slowly added two - five drops of concentrated sulfuric acid, H2SO4, onto one spatula sample of potassium iodide, KI, in a test tube. This reaction was carried out in a fume cupboard.

The student recorded their observations which are outline below:

  • Yellow solid produced
  • Smell of bag eggs
  • Purple vapour

Identify the substances responsible for the observations that the student has recorded.

3d3 marks

When the student reacted solid potassium bromide with concentrated sulfuric acid using the same method outline in part (c) the observations were: 

  • Reddish brown fumes
i)
Give the name of the substance responsible for the reddish brown fumes.

ii)
In this reaction sulfur dioxide, SO2, was also produced. Balance the equation below:
SO42- + ___ H+ + ___ e-  →  SO2 +  ___ H2O

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4a1 mark

State what is meant by the term ‘disproportionation reaction’.

4b3 marks

The reaction between chlorine and an alkali is an example of a disproportionation reaction.

Write an equation, including state symbols, for the reaction between dilute sodium hydroxide, NaOH (aq) and chlorine, Cl2 (g), at 70 degreeC.

4c3 marks

Chlorine is added to drinking water and used in swimming pools to kill any potentially harmful bacteria.

The equation below shows the reaction between chlorine and water. The oxidation numbers of chlorine are shown

0       -1   +1
Cl2 (aq) + H2O (l) HCl (aq) + HOCl (aq)

Use the oxidation numbers to explain why this is an example of a disproportionation reaction.

4d2 marks

Chlorine, Cl2, is a toxic substance. Suggest why adding chlorine to the drinking water supply is safe to do so. 

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5a1 mark

Chlorine, Cl2, can displace bromine, Br2, from a solution of potassium bromide, KBr. Give the simplest ionic equation for this reaction.

5b1 mark

In the reaction outlined in part (a), chlorine, Cl2, is acting as an oxidising agent.            

Order the halogens below from the strongest to weakest oxidising agent.

  • Bromine, Br2
  • Chlorine, Cl2
  • Iodine, I2
5c2 marks

Iodide ions are stronger reducing agents than bromide ions.

When solid potassium iodide, KI, and concentrated sulfuric acid, H2SO4, are reacted in a test tube iodine, I2, and sulfur, S, are produced.

i)
Give the half equation for the production of sulfur, S, from concentrated sulfuric acid, H2SO4.

ii)
Give the half equation for production of iodine, I2, from iodide ions, I-.
5d2 marks

Using the half equations from part (c) give the full redox equation for the reaction between concentrated sulfuric acid, H2SO4, and iodide ions, I-, to produce iodine, I2, and sulfur, S.

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1a4 marks

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. 

1b2 marks

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 provide an equation for the reaction of chlorine with cold water.

1c1 mark

Chlorine will also react with cold, dilute sodium hydroxide. 

Provide the equation for this reaction.

1d6 marks

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. 

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2a6 marks

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.

2b3 marks

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.

2c1 mark

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.

2d3 marks

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.

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3a4 marks

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.

3b6 marks

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. 

Provide relevant equations to justify your answer.

3c3 marks

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

3d1 mark

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. 

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4a5 marks

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.
4b3 marks

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.

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

4c5 marks

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.
4d1 mark

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.

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5a6 marks

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

Unknown

Test

Result

X

Added acidified silver nitrate solution

 Then added concentrated ammonia

Yellow precipitate formed

Precipitate remained

Y

Added barium chloride solution

White precipitate formed

Z

Added acidified silver nitrate solution

 Then added concentrated ammonia

Cream precipitate formed

 Precipitate dissolved

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.

5b2 marks

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.

5c3 marks

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. 

5d3 marks

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.

Is Student A, Student B or neither student correct? Justify your answer. 

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1a6 marks

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

1b3 marks

A student reacted solid potassium bromide with concentrated sulfuric acid.

i)
Give the half equations and the full equation for the conversion of H2SO4 to S and Br- to Br2.

ii)
Give the full equation from the half equations outlined in part (b) (i).
1c2 marks

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.

1d4 marks

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.

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2a4 marks

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.
2b2 marks

A student states that in the reaction in part (a) chlorine oxidises the water. Is the student correct? Justify your answer.

2c1 mark

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.

2d2 marks

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.

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3a4 marks

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.
3b2 marks

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.

3c2 marks

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-.

3d2 marks

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

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4a2 marks

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

Figure 1

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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.

4b2 marks

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

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4c2 marks

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.

4d4 marks

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. 

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5a5 marks

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.
5b6 marks

Table 1 shows the boiling points of some halogenoalkanes.

Table 1

Compound

CH3CH2CH2F

CH3CH2CH2Cl

CH3CH2CH2Br

CH3CH2CH2I

Boiling Point (°C)

-2.5

46.6

71.0

102.5

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.

5c5 marks

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+

i
ii)
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).
5d3 marks

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.

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