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  4. 20 mL of 0.02 M hypo solution is used for the titration of 10 mL of copper sulphate solution, in the presence of excess of KI using starch as an indicator. The molarity of Cu 2+ is found to be × 10-2 M [nearest integer] Given: 2 Cu 2++4 I - arrow Cu 2 I 2+ I 2 I 2+2 S 2 O 3 2- arrow 2 I -+ S 4 O 6 2-

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Q. $20\, mL$ of $0.02\, M$ hypo solution is used for the titration of $10 mL$ of copper sulphate solution, in the presence of excess of KI using starch as an indicator. The molarity of $Cu ^{2+}$ is found to be______ $\times 10^{-2} M$ [nearest integer]
Given : $2 Cu ^{2+}+4 I ^{-} \rightarrow Cu _2 I _2+ I _2$
$I _2+2 S _2 O _3{ }^{2-} \rightarrow 2 I ^{-}+ S _4 O _6{ }^{2-}$

JEE MainJEE Main 2022Redox Reactions

Solution:

$ n _{\text {eq. }} \text { of } I _2= n _{ eq } \text { of } Na _2 S _2 O _3=20 \times 0.002 \times 1 $
$ 2 \times n _{ mol } \text { of } I _2=0.4 $
$ n _{ mol } \text { of } I _2=0.2 m mol $
$ n _{ mol } \text { of } Cu ^{+2}=0.2 \times 2 \times 10^{-3} $
$ {\left[ Cu ^{+2}\right]=\frac{0.4 \times 10^{-3}}{10 \times 10^{-3}}=0.04=4 \times 10^{-2}}$