An ozone-containing gas sample is passed into excess acidified KI. The iodine liberated needed 28.40 mL of 0.1050 M sodium thiosulphate. Use O3 + 2I- + H2O -> I2 + O2 + 2OH- and I2 + 2S2O3^2- -> 2I- + S4O6^2- and take O = 16. Find the mass of ozone in the sample in mg, to two decimals.

JEE Advanced levelNumerical answerDifficulty 3 of 3pn194

An ozone-containing gas sample is passed into excess acidified KI. The iodine liberated needed 28.40 mL of 0.1050 M sodium thiosulphate. Use $O X_{3} + 2 I X^{-} + H X_{2} O I X_{2} + O X_{2} + 2 OH X^{-}$ and $I X_{2} + 2 S X_{2} O X_{3} X^{2 -} 2 I X^{-} + S X_{4} O X_{6} X^{2 -}$ and take O = 16. Find the mass of ozone in the sample in mg, to two decimals.

Numerical answer type, answer in mg, tolerance 0.01.

Moles of thiosulphate =

0.105 \times 28.4/1000 = 0.002982

. Ozone : iodine : thiosulphate = 1 : 1 : 2, so moles of

O X_{3}

= 0.0014910. Mass = moles

\times 48

g/mol = 71.57 mg.