Disproportionate reactions

Disproportionate reactions

Reactions where the same element is both oxidised and reduced

Halogen reactions

Halogens can undergo disproportionate reactions with cold dilute alkali solutions

Halogen disproportionate reaction equation

X2 + 2NaOH ——→ NaX0 +NaX + H20

Halogen disproportionate reaction ionic equation

X2 + 2OH- ——> XO + X- + H2O

Scientific name for bleach

Sodium chlorate solution

How to make bleach

You have to react chlorine gas and cold dilute aqueous sodium hydroxide

Bleach reaction equation

2NaOH (aq) + Cl2 (g) ——→ NaClO (aq) + NaCl (aq) + H20 (l)

Bleach formula

NaClO

Chlorine and water reaction equation

Cl (g) + H20 ← → HCl (aq) + HClO (aq)

How to form water treatment from chlorine and water reaction

Aqueous chloric I acid ionises to make chlorate I ions (also known as hypochlorite ions) which can kill bacteria

Chlorine water treatment reaction

HClO (aq) + H20 (l) ← → ClO- + H3O+

Benefits of chlorine water treatment

Kills pathogens, some chlorine remains in the water preventing reinfection in the future, prevents algal growth stopping bad tastes and smells and removes discolouration caused by organic compounds

Risks of chlorine water treatments

Chlorine gas is toxic as it’s harmful when inhaled as it irritates the respiratory tract, liquid chlorine can cause chemical burns to the skin and eyes and the chlorine can react with organic compounds in the water to form chlorinated hydrocarbons some of which are carcinogenic (cause cancer)

Alternative methods to chlorine water treatment

Ozone and ultraviolet light

How to use ozone (O2) as a water treatment

Ozone is a strong oxidising agent so kills microorganisms

Cons of ozone use

It’s expensive to produce and has a hurt half-life so isn’t permanent

How to use ultraviolet light as water treatment

Kills micro-organisms by damaging their DNA

Cons of ultraviolet light as water treatment

It’s ineffective in cloudy water and doesn’t stop contamination in the future