source :

Chemical properties:

1) Reaction with KI :

Iodine is soluble in KI due to formation of Potassium tri iodide complex(brown complex)

KI+I2 —–> KI3

2) Reaction with NaOH

a) With Cold and dilute NaOH : sodium iodide &sodium hypo iodite is formed.

2NaOH +I2 ——> NaI +NaIO +H2O

b) Hot and concentrated NaOH : 

sodium iodide & sodium iodate is formed.

6NaOH + 3I2 ——> NaIO3 + 5NaI + 3H2O

3) Reaction with NH3 :

nitrogen tri-iodide ammonia is formed which is an  explosive. It explodes on heating or rubbing.

5NH3 + 3I2 ——> NI3.NH3 [nitrogen tri-iodide ammonia (explosive)] + 3NH4I

NI3.NH3  ——–> N2 +I2 +NH4I

4) Oxidizing properties :

Iodine is weak oxidizing agent.

a) It oxidizes SO2 into H2SO4:

I2 +H2O ——> 2HI + O

SO2 + [O] +H2O —–>H2SO4

Equation as a whole ,

I2 + 2H2O +SO2 ——>H2SO4 +2HI

b) It oxidizes Na3AsO3 to Na3AsO4:

I2 +H2O —–> 2HI + O

Na3AsO3  + O ——-> Na3AsO4

Equation as a whole ,

I2 +H2O + Na3AsO3 ——> 2HI + Na3AsO4

c) It oxidizes H2S into S:

I2 + H2O ——> 2HI +O

H2S +O ——> H2O + S

Equation as a whole ,

I2 +H2S ——->2HI + S

d) It oxidizes hypo into  sodium tetrathionate.

2Na2S2O3 (hypo) + I2  ——> 2NaI +Na2S4O6 (sodium tetrathionate)

e) It oxidizes SnCl2 to SnCl4 :

SnCl2 +2HCl +I2 ——-> SnCl4 +2HI

5) Reaction with oxidizing agents:

Oxidizing agent oxidizes I2 into Iodic acid.

a) Oxidation by Chlorine :

5Cl2 +5H2O ——> 10 HCl + 5 [O]

I2 + 5 [O] +H2O —–>2HIO3

Equation as a whole,

5Cl2 + 6 H2O + I2 ——–> 2HIO3 +10HCl

b) Oxidation by Nitric acid :

[2HNO3 —–> H2O + 2NO2 + [O]] x 5

10 HNO3 ——->5 H2O +10 NO2 +5 [O]

I2 +5 [O] +H2O —–>2HIO3

Equation as a whole,

10HNO3 +I2 ———> 2HIO3 +10 NO2 +4H2O

c) Oxidation by Ozone :

5O3 ——-> 5O2 +5 [ O]

I2 + 5[O] +H2O ——>2HIO3PO

Equation as a whole,

5O3 + I2 +H2O —–>5O2 + 2HIO3

6) Basic properties of I:

Iodine has weak tendency to form cation. Basic property  of I2  is due to formation of cation.

ICl ——> I+ + Cl

IPO4 ——>I3+ + PO43-

Test of Iodine :

1) It gives violet color with starch.

2)On heating the solution of C2H5OH, NaOH and I2, yellow precipitate of iodoform are obtained.


  1. Colloidal solution of I2 is used in the treatment of goitre(in this disease throat swells up).
  2. In making iodoform test in lab.
  3. In  preparing  tincture of iodine which is used as disinfectant. Tincture of iodine is prepared by dissolving iodine in rectified spirit.