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ChemistryInteger+4 / -1Question 85 of 90

JEE Main 2022 · 26 Jul · Shift 2, Chemistry question 85

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 Cu2+\mathrm{Cu^{2+}} is found to be ______ ×10−2\times10^{-2} M. [nearest integer]

Given : 2Cu2++4I−→Cu2I2+I2\mathrm{2Cu^{2+}+4I^-\rightarrow Cu_2I_2+I_2}

I2+2S2O32−→2I−+S4O62−\mathrm{I_2+2S_2O_3^{2-}\rightarrow2I^-+S_4O_6^{2-}}

Answer and worked solution

Official answer: 4

Stoichiometry. 2 Cu2+\mathrm{Cu^{2+}} → 1 I2\mathrm{I_2} → 2 hypo, so mmol Cu2+\mathrm{Cu^{2+}} = mmol hypo =20×0.02=0.4=20\times0.02=0.4.

Molarity 0.410=0.04\frac{0.4}{10}=0.04 M =4×10−2=4\times10^{-2} M.

Answer: 4

Topics:Redox titrations
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