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Method of preparation:
1) By passing Cl2 or Br2 in aqueous KI solution :
2KI +Cl2 ——-> 2KCl +I2
2KI + Br2 ——-> 2KBr +I2
2) By the oxidation of KI(Potassium iodide) :
(a) H2O2 ——> H2O + O
2KI +H2O + O —–> 2KOH +I2
Equation as a whole
2KI +H2O2 ——> 2KOH + I2
(b) O3 —-> O2 + O
2KI +H2O+O —–> 2KOH +I2
Equation as a whole
2KI +H2O + O3 —–> 2KOH +I2 +O2
3) By the reaction of KI ( Potassium iodide) and copper sulphate :
CuSO4 + 2KI ——->K2SO4 +CuI2 (cupric iodide)
2CuI2 ——>2CuI (cuprous iodide, white precipitate) +I2
4) By heating a mixture of KI , MnO2 and H2SO4 :
2KI + MnO2 + 3H2SO4 ——> MnSO4 + 2 KHSO4 + 2H2O + I2
5) By the reaction of sodium Iodate and sodium bi-sulphite :
2NaIO3 + 5 NaHSO3 ——–>2 Na2SO4 + 3 NaHSO4 + I2+ H2O
6) By the reaction of KI and KIO3 with concentrated H2SO4:
5KI +KIO3 + 6 H2SO4 ——> 6 KHSO4 + 3 H2O + 3I2
Manufacture of Iodine from Sea Weeds :
Iodine is present in sea weeds such as Laminaria digitata and Laminaria stenophylla in the form of KI and NaI. Sea weeds are collected, dried and then burnt in shallow pits to obtained their ash which is called kelp.It contains 0.5 to 1.3 % iodine in the form of KI and NaI.
Kelp is shaken with hot water then KI , NaI and impurities of NaCl, KCl, Na2SO4, Na2CO3 etc. come in solution. On cooling the solution impurities separate out while NaI and KI remain in solution. Concentrated H2SO4 and MnO2 is added in mother liquor. Mother liquor is solution of NaI and KI . It is heated in an iron retort.Vapours of iodine are formed which are condensed in series of aludels.
2NaI + MnO2 + 3H2SO4 ——> 2 NaHSO4 + MnSO4 + I2 + 2H2O
2KI + MnO2 + 3H2SO4 ——> 2 KHSO4 + MnSO4 + I2 + 2H2O
Manufacture of Iodine from Caliche :
Chile saltpeter (NaNO3) contains 5-20 % NaIO3. Chile saltpeter is also known as caliche. It is an important source of iodine. Aqueous solution of caliche is prepared which on concentration gives crystal of NaNO3. Crystals are filtered out. The filtrate contains NaIO3. Required amount of NaHSO3 is added in the filtrate. Iodine separates out.
2NaIO3 + 5 NaHSO3 ———-> 3 NaHSO4 + 2Na2SO4 + H2O + I2
Purification of Iodine :
Iodine obtained by above method contains the impurity of ICl, IBr, ICN. These impurities are volatile and therefore these impurities can not be removed by sublimation method.Because iodine also have sublimation property so KI is mixed with impure I2 and heated . Then vapours of pure I2 are formed which are condensed.
ICl + KI ——> KCl +I2
IBr +KI ——->KBr +I2
ICN +KI ——->KCN +I2
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- It is dark violet crystalline solid.
- Iodine has metallic lustre.
- Iodine sublimes on heating.
- Vapours of iodine are poisonous.
- It is sparingly soluble in water.