Uses of Chlorine
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What happens when chlorine gas dissolves in water?
Water is sterilised. Chlorine reacts with water to form H+ ions, Cl- ions and chlorate ions (ClO-)
Write the equation for the reaction of chlorine with water Hint: (g, l, aq, aq, aq)
Cl2 (g) + H2O (l) -> HCIO (aq) + HCl (aq)
What type of reaction occurs when chlorine reacts with water? Prompt; what happens to chorine
A disproportionation reaction, where chlorine is both oxidised and reduced
Why is the disproportionation reaction between chlorine and water, important in everyday life?
The reactions produces chlorate ions (ClO-) which kills bacteria, making the water drinkable and safe to use in swimming pools
Risks associated with chorine despite its usefulness? (toxic = respiratory, chloroalkanes = cancer)
• Chlorine gas is toxic, can irritate the respiratory systems • Chlorine can react with organic compounds to form chloroalkanes, which have been linked with causing cancer
How do the reactions of other halogens with water compare to chlorine?
The other halogens react similarly to chlorine but more slowly as you go down the group
Pool water that is under sunlight loses chlorate ions rapidly, so why do shallow swimming pools need frequent addition of chlorine?
The sunlight breaks down the chlorate ions, removing the active agent killing the bacteria, as a result, making the swimming pool water unsafe
What is done to maintain chlorine levels in sunlight?
Frequent addition of chlorine or the use of chlorate salts that release HClO gradually
Write the equation that occurs between water and chlorine when under direct sunlight hint: (l,g,aq,aq,g)
2H2O (l) + Cl2 (g) → 4H+ (aq) + 2Cl- (aq) + O2 (g)
What is an alternative to directly adding chlorine gas to swimming pools?
Adding solid sodium chlorate (NaClO) or calcium chlorate (CaClO)
What happens when sodium or calcium chlorate dissolves in water?
Either will form chloric acid (HClO) in a reversible reaction
Write the equation for the formation of chloric acid from sodium chlorate
NaClO (s) + H2O (l) ⇌ HClO (aq) + NaOH (aq)
Why is sodium (or calcium) chlorate sometimes preferred over chlorine gas for pool treatment?
It provides a safer and more controlled way to produce chloric acid, maintaining disinfection without handling toxic chlorine gas
Role of chloric acid (HClO) in pool water?
It acts as a disinfectant, killing bacteria and other microorganisms
Why must swimming pools be kept slightly acidic?
To prevent the equilibrium shifting left and losing chloric acid (HClO), which is needed for disinfection
Why isn’t pool water made too acidic?
Because too much acidity could corrode metal components and harm swimmers
What happens when chlorine reacts with cold, dilute sodium hydroxide?
It forms sodium chlorate (NaClO), sodium chloride (NaCl), and water
Write the equation for chlorine reacting with cold, dilute sodium hydroxide
Cl2 (g) + 2NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l)