10.4 Flashcards
what is a disproportionation reaction?
A redox reaction where the oxidation state of some atoms in the same species increases while some decrease.
what is the reaction of chlorine gas with water?
In the reaction of chlorine with water, chloric (I) acid and hydrochloric acid are formed in a reversible reaction:
Cl2 (aq) + H2O (l) <=> HClO (aq) + HCl (aq)
The oxidation state of one chlorine atom increases while the other decreases therefore it is a disproportionation reaction.
what is the reaction between chlorine gas and a cold alkali? what is the chemical and ionic equation for the reaction?
When chlorine reacts with cold, dilute sodium hydroxide, sodium chlorate(I) is formed:
Cl2 (aq) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)
The ionic equation is:
Cl2 (aq) + 2OH– (aq) → Cl– (aq) + ClO– (aq) + H2O (l)
Chlorine gets oxidized:
½Cl2 (aq) + 2OH– (aq) → ClO– (aq) + H2O (l) + e–
chlorine gets reduced:
½Cl2 (aq) + e– → Cl– (aq)
How can chlorine be used for water treatment?
When chlorine reacts with water, chloric(I) acid and hydrochloric acid are formed.
Chloric(I) acid, HClO, sterilises water by killing bacteria. In shallow swimming pools, chlorine is rapidly lost from the water due to its exposure to sunlight
In sunlight, the following reaction occurs:
2Cl2 (g) + 2H2O (l) → 4HCl (aq) + O2 (g)
The chlorine has to be topped up regularly increasing costs
How can sodium chlorate (l) be used for water treatment?
An alternative to directly adding chlorine to water is to add chlorate ions, ClO- in the form of sodium or calcium chlorate(I)
NaClO (aq) + H2O (l) → Na+ (aq) + OH- (aq) + HClO- (aq)
ClO- (aq) acts as a sterilising agent cleaning the water
What are the issues with using chlorine as water treatment?
Chlorine is a toxic substance so the levels of chlorine in water and swimming pools have to be carefully monitored
There needs to be enough chlorine present to kill bacteria and sterilise the water without causing any harm to us
Generally, the benefits to our health of adding chlorine to water outweigh its toxic effects and possible risks from the formation of chlorinated hydrocarbons
