Group 7

True or false? The halogens exist diatomically.

True.

What does fluorine look like (state and colour)?

Pale yellow gas.

What does chlorine look like (state and colour)?

Pale green gas.

What does bromine look like (state and colour)?

Brown-orange liquid.

What does iodine look like (state and colour)?

Grey solid.

Describe and explain the trend in boiling points going down group 7.

Boiling point increases going down group 7. Increasing size and relative mass of the atoms increases the Van der Waals forces, which requires more energy (higher temperatures) to overcome.

Describe and explain the trend in electronegativity going down group 7.

Electronegativity decreases going down group 7. The increasing atomic radius due to increasing number of electrons in the atom going down group 7 means that there is a decreased attraction between the outer shell of electrons and the nucleus and more shielding, making it harder to gain electrons.

True or false? Less reactive halogens will displace more reactive halide ions in a compound.

False. MORE REACTIVE HALOGENS WILL DISPLACE LESS REACTIVE HALIDE IONS IN A COMPOUND.

Describe and briefly explain the trend in reactivity going down the halogens.

Reactivity decreases going down the halogens. This is because, in general, a halogen must gain an electron to have reacted and electronegativity decreases going down the halogens, so so will reactivity.

Describe and explain the trend in oxidising ability going down group 7.

Oxidising ability (ability to be reduced itself) decreases going down group 7. As weaker attraction between outer shell of electrons and nucleus and more shielding it becomes harder to gain electrons from other species (oxidise other species).

Give the balanced symbol equation for the reaction between chlorine and a compound containing bromide ions. What observations will be made?

Cl₂ + 2Br^- → 2Cl^- + Br₂

Orange solution formed (Br2).

Give the balanced symbol equation for the reaction between chlorine and a compound containing iodide ions. What observations should be made?

Cl₂ + 2I^- → 2Cl^- + I₂

Brown solution formed (I₂).

Give the balanced symbol equation for the reaction between bromine and a compound containing iodide ions. What observations should be made?

Br2 + 2I^- → 2Br^- + I2

Will chlorine react with a compound containing bromide ions? Explain your answer.

Yes. Chlorine is more reactive than bromine so will displace bromide ions in a compound.

Will chlorine react with a compound containing iodide ions? Explain your answer.

Yes. Chlorine is more reactive than iodine so will displace iodide ions in a compound.

Will bromine react with a compound containing chloride ions? Explain your answer.

No. Bromine is less reactive than chlorine so no displacement reaction will take place.

Will bromine react with a compound containing iodide ions? Explain your answer.

Yes. Bromine is more reactive than iodine so will displace iodide ions in a compound.

Will iodine react with a compound containing chloride ions? Explain your answer.

No. Iodine is less reactive than chlorine so no displacement reaction will take place.

Will iodine react with a compound containing bromide ions? Explain your answer.

No. Iodine is less reactive than bromine so no displacement reaction will take place.

What type of reaction makes bleach?

A disproportionation reaction.

What is a disproportionation reaction?

A redox reaction in which the same element is simultaneously oxidised and reduced.

What IS bleach?

Sodium chlorate (I) solution.

What two reagents can you mix to make bleach?

Chlorine and sodium hydroxide.

Give the balanced symbol equation for the reaction between chlorine and sodium hydroxide to form bleach.

2NaOH (aq) + Cl₂ (g) → NaClO (aq) + NaCl (aq) + H₂O (l)

Which element is simultaneously oxidised and reduced in the formation of bleach?

Chlorine.

Give three uses of bleach.

• Cleaning agent

• Bleaching paper/fabrics

• Sterilising water

What in the products of the reaction between chlorine and water actually kills bacteria?

Chlorate ion (ClO^-).

Give the balanced symbol equation for the reaction between chlorine and water.

H2O (l) + Cl2 (g) → ← 2H^+ (aq) + Cl^- (aq) + ClO^- (aq) (OR products appear as HCl and HClO).

Give the balanced symbol equation for the reaction between water and chlorine in the presence of sunlight.

2H₂O (l) + Cl₂ (g) → 4H⁺ (aq) + 2Cl^- (aq) + O₂ (g) (OR products could appear as O2 and HCl).

What is the issue with sunlight decomposing chlorinated water?

No chlorate ions are produced meaning bacteria aren’t killed so the water isn’t sterilised.

Give three advantages of chlorinating drinking water.

• It destroys microorganisms that cause disease.

• They are long-lasting so prevent build up of harmful microorganisms further down the line.

• They prevent the growth of algae that gives the water a bad colour, smell, and taste.

Give three disadvantages of chlorinating drinking water.

• Chlorine gas is toxic and a respiratory irritant.

• Liquid chlorine causes chemical burns when into comes into contact with skin.

• Chlorine can react with organic compounds to form cancer-linked chloroalkanes.

Why are halide ions such good reducing agents?

Halide ions are likely to lose the electron that they gained (and donate it to other species, thus reducing them).

Describe and explain the trend in reducing ability of the halide ions going down group 7.

Reducing ability increases going down group 7. Ionic radius increases going down group 7 so the distance between the nucleus and the outer shell of electrons increases so decreases their attraction, shielding increases too. This makes it easier to lose an electron (and reduce another species).

What two reactions can you carry out to prove the trend in reducing ability of the halide ions?

• Reaction with sulfuric acid.

• Reaction with silver nitrate solution.

True of false? Some halide ions can reduce concentrated sulfuric acid.

True.

How do the reactions with sulfuric acid prove the trend in reducing ability of the halide ions?

Depending on the product formed, sulfur will have a different oxidation state in each different product. The lower the oxidation state of sulfur the more sulfur has been reduced and the greater the reducing power of the halide ion.

What are four possible products that contain sulfur for the reactions between halide ions and sulfuric acid?

NaHSO₄, SO₂, S, H₂S.

How many reactions happen when chloride ions react with sulfuric acid?

One.

How many reactions happen when bromide ions react with sulfuric acid?

Two.

How many reactions happen when iodide ions react with sulfuric acid?

Four (iodide ions strongest reducing agent).

What is the source of halide ions in the reactions between halide ions and sulfuric acid?

Sodium halides.

Write the balanced symbol equation for the reaction between sodium chloride and sulfuric acid. Describe and explain the observations for this reaction.

H₂SO₄ + NaCl → NaHSO₄ + HCl

White misty fumes (HCl).

Write the balanced symbol equation for the FIRST reaction between sodium bromide and sulfuric acid. Describe and explain any observations in this reaction.

H₂SO₄ + NaBr → NaHSO₄ + HBr

White misty fumes (HBr)

Write the balanced symbol equation for the SECOND (and final) reaction between bromide ions and sulfuric acid. Describe and explain any observations made.

H2SO4 + 2H^+ + 2Br^- → Br2 + SO2 + 2H2O

Orange vapour (Br2)

Write the balanced symbol equation for the FIRST reaction between sodium iodide and sulfuric acid. Describe and explain any observations made.

H2SO4 + NaI → NaHSO4 + HI

White misty fumes (HI)

Write the balanced symbol equation for the SECOND reaction between iodide ions and sulfuric acid. Describe and explain any observations made.

H₂SO₄ + 2H⁺ + 2I^- → I₂ + SO₂ + 2H₂O

Purple vapour (I2)

Write the balanced symbol equation for the THIRD reaction between iodide ions and sulfuric acid. Describe and explain any observations made.

H₂SO₄ + 6H⁺ + 6I^- → 3I₂ + S + 4H₂O

Yellow solid formed (S)

Write the balanced symbol equation for the FOURTH (and final) reaction between iodide ions and sulfuric acid. Describe and explain any observations made.

H₂SO₄ + 8H⁺ + 8I^- → 4I₂ + H₂S + 4H₂O

Rotten egg smell (H2S).

Talk me through the process of identifying halide ions with acidified silver nitrate solution.

1) Add some acidified silver nitrate to the test tube sample.

2) Look at the colour of the precipitate formed (white ppt = chloride ions, cream ppt = bromide ions, yellow ppt = iodide ions).

Why is silver nitrate acidified when testing for halide ions?

The acid reacts with any other anions that may be present in the sample so that there are no false positive results.

What is the white precipitate when testing with acidified silver nitrate? Give the ionic equation for how this precipitate is formed.

AgCl (silver chloride). Ag⁺ + Cl^- → AgCl

What is the cream precipitate formed when testing with acidified silver nitrate? Give the ionic equation for how it is formed.

AgBr (silver bromide). Ag⁺ + Br^- → AgBr

What is the yellow precipitate formed when testing with acidified silver nitrate? Give the ionic equation for how it is formed.

AgI (silver iodide). Ag^+ + I^- → AgI

How does the solubility of the silver halides in ammonia change going down group 7?

Solubility in ammonia decreases going down group 7.

How can you confirm the presence of a halide ion with ammonia (after the acidified silver nitrate solution test)?

1) Add dilute ammonia to the test tube (if the precipitate dissolves, chloride ions are present).

2) Add concentrated ammonia to the test tube (if the precipitate dissolves, bromide ions are present).

• If no ammonia seem to dissolve the precipitate, then iodide ions are present in the sample.