Some Basic Concepts of Chemistry - Result Question 34
Subjective Questions
34. An aqueous solution containing $0.10 g KIO _3$
$($ formula weight $=214.0)$ was treated with an excess of KI solution. The solution was acidified with $HCl$. The liberated $I _2$ consumed $45.0 mL$ of thiosulphate solution decolourise the blue starch-iodine complex. Calculate the molarity of the sodium thiosulphate solution.
$(1998,5 M)$
Show Answer
Answer:
Correct Answer: 34. (0.062 M)
Solution:
The redox reaction involved are
$\begin{aligned} & \mathrm{IO}_3^{-}+5 \mathrm{I}^{-}+6 \mathrm{H}^{+} \longrightarrow 3 \mathrm{I}_2+3 \mathrm{H}_2 \mathrm{O} \\ & \mathrm{I}_2+2 \mathrm{~S}_2 \mathrm{O}_3^{2-} \longrightarrow 2 \mathrm{I}^{-}+\mathrm{S}_4 \mathrm{O}_6^{2-} \\ & \text { millimol of } \mathrm{KIO}_3 \text { used }=\frac{0.1}{214} \times 1000=0.467 \\ & \Rightarrow \text { millimol of } \mathrm{I}_2 \text { formed }=3 \times 0.467=1.4 \\ & \Rightarrow \text { millimol of } \mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3 \text { consumed }=2 \times 1.4=2.8 \\ & \Rightarrow \text { Molarity of } \mathrm{Na}_2 \mathrm{~S}_2 \mathrm{O}_3=\frac{2.8}{45}=0.062 \mathrm{M} \\ & \end{aligned}$
BETA
