Redox Reactions in Group 7

Inorganic Chemistry of Group 7

How do Group 1 and Group 2 metals react with Group 7 halogens?

They react to form ionic salts.

What is the general trend in vigour of reactions between Group 1 or 2 metals and halogens?

Reactions are most vigorous with metals lower down Groups 1 and 2 and halogens higher up Group 7.

What type of reaction occurs between metals and halogens?

A redox reaction involving electron transfer.

What happens to the halogen during a reaction with a metal?

The halogen gains electrons and is reduced.

What happens to the metal during a reaction with a halogen?

The metal loses electrons and is oxidised.

What happens to the oxidation number of a halogen when it reacts with a metal?

It decreases from 0 to −1.

What happens to the oxidation number of a Group 1 metal when it reacts with a halogen?

It increases from 0 to +1.

What happens to the oxidation number of a Group 2 metal when it reacts with a halogen?

It increases from 0 to +2.

What role does the halogen have in reactions with metals?

It acts as an oxidising agent.

What is the equation for lithium reacting with chlorine?

2Li + Cl₂ → 2LiCl

What is the equation for barium reacting with bromine?

Ba + Br₂ → BaBr₂

What is a halogen displacement reaction?

A reaction in which a more reactive halogen displaces a less reactive halogen from a compound containing its halide ions.

What is the order of reactivity of chlorine, bromine and iodine?

Chlorine > bromine > iodine.

Which halogens can chlorine displace from their halides?

Bromine and iodine.

Which halogen can bromine displace from its halide?

Iodine.

Can bromine displace chlorine from a chloride?

No.

Can iodine displace chlorine or bromine from their halides?

No.

What is the equation for chlorine displacing bromine from sodium bromide?

Cl₂ + 2NaBr → 2NaCl + Br₂

What is the ionic equation for chlorine displacing bromine?

Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

What is the ionic equation for bromine displacing iodine?

Br₂ + 2I⁻ → 2Br⁻ + I₂

Why are halogen displacement reactions redox reactions?

The reacting halogen is reduced from oxidation number 0 to −1 while the displaced halide is oxidised from −1 to 0.

Why is chlorine more reactive than bromine and iodine?

Chlorine is smaller and has fewer occupied electron shells, so there is less shielding and the nucleus attracts an incoming electron more strongly.

Why does halogen reactivity decrease down Group 7?

Atomic radius and electron shielding increase, so the attraction between the nucleus and an incoming electron decreases.

Why is an organic solvent such as cyclohexane added after a halogen displacement reaction?

Halogens are more soluble in cyclohexane than in water, making their colours easier to identify.

Where does the halogen dissolve when cyclohexane is added?

In the organic upper layer.

What colour is chlorine in cyclohexane?

Pale green.

What colour is bromine in cyclohexane?

Orange.

What colour is iodine in cyclohexane?

Purple or violet.

What is disproportionation?

A reaction involving the simultaneous oxidation and reduction of an element in a single species.

What happens when chlorine is added to water?

It disproportionates to form hydrochloric acid and chloric(I) acid.

What is the equation for chlorine reacting with water?

Cl₂ + H₂O ⇌ HCl + HClO

What happens to the oxidation number of chlorine when chlorine reacts with water?

Some chlorine is reduced from 0 to −1 and some is oxidised from 0 to +1.

Which chlorine-containing product is formed by reduction when chlorine reacts with water?

HCl, where chlorine has oxidation number −1.

Which chlorine-containing product is formed by oxidation when chlorine reacts with water?

HClO, where chlorine has oxidation number +1.

What is another name for HClO?

Chloric(I) acid.

Why has chlorine traditionally been added to drinking water and swimming pools?

It kills pathogenic microorganisms and therefore disinfects the water.

What happens when chlorine reacts with cold dilute sodium hydroxide?

It disproportionates to form sodium chloride, sodium chlorate(I) and water.

What is the equation for chlorine reacting with cold dilute NaOH?

Cl₂ + 2NaOH → NaCl + NaClO + H₂O

What is the oxidation number of chlorine in Cl₂?

0.

What is the oxidation number of chlorine in NaCl?

−1.

What is the oxidation number of chlorine in NaClO?

+1.

Which chlorine product is formed by reduction in the reaction with cold dilute NaOH?

NaCl.

Which chlorine product is formed by oxidation in the reaction with cold dilute NaOH?

NaClO.

What is the systematic name of NaClO?

Sodium chlorate(I).

What is another common name for the ClO⁻ ion?

Hypochlorite.

What is sodium chlorate(I) mainly used for?

Bleaching and disinfection.

What happens when chlorine reacts with hot concentrated sodium hydroxide?

It disproportionates to form sodium chloride, sodium chlorate(V) and water.

What is the equation for chlorine reacting with hot concentrated NaOH?

3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O

What happens to chlorine's oxidation numbers in its reaction with hot concentrated NaOH?

Chlorine is reduced from 0 to −1 and oxidised from 0 to +5.

Which product contains the reduced chlorine when chlorine reacts with hot concentrated NaOH?

NaCl.

Which product contains the oxidised chlorine when chlorine reacts with hot concentrated NaOH?

NaClO₃.

What is the systematic name of NaClO₃?

Sodium chlorate(V).

What are uses of sodium chlorate(V)?

It is used in bleaching and as a weed killer.

How do bromine and iodine react with alkalis compared with chlorine?

They undergo similar disproportionation reactions.

What products form when bromine reacts with cold dilute NaOH?

Sodium bromide, sodium bromate(I) and water.

What is the equation for bromine reacting with cold dilute NaOH?

Br₂ + 2NaOH → NaBr + NaBrO + H₂O

What products form when bromine reacts with hot concentrated NaOH?

Sodium bromide, sodium bromate(V) and water.

What is the equation for bromine reacting with hot concentrated NaOH?

3Br₂ + 6NaOH → 5NaBr + NaBrO₃ + 3H₂O

How can reactions of fluorine and astatine be predicted?

Use the trends and reactions of the other Group 7 elements.

Which is more reactive, fluorine or chlorine?

Fluorine.

Which is less reactive, astatine or iodine?

Astatine.

What is the predicted equation for sodium reacting with astatine?

2Na + At₂ → 2NaAt

What is the ionic equation for bromine reacting with astatide ions?

Br₂ + 2At⁻ → 2Br⁻ + At₂

Why can bromine displace astatine from astatide ions?

Bromine is higher in Group 7 and is more reactive, so it gains electrons more readily than astatine.