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Class 12
Chemistry :-NCERT Solution - p Block elements

Exercise 1 Question 19
How is Oestimated quantitatively?


Answer:

Quantitatively, ozone can be estimated with the help of potassium iodide. When ozone is made to react with potassium iodide solution buffered with a borate buffer (pH 9.2), iodine is liberated. This liberated iodine can be titrated against a standard solution of sodium thiosulphate using starch as an indicator. The reactions involved in the process are given below.

2I-     +    H2O   +   O3    →   2OH-    +    I2    +   O2

Iodide             Ozone                       Iodine

I2     +   2Na2S2O3         →      Na2S4O6     +     NaI

              Sodium                     Sodium  

           thiosulphate                tetrathionate