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ChemistryNumerical+4Question 31 of 54

JEE Advanced 2020 · Paper 1, Chemistry question 13

5.00 mL of 0.10 M oxalic acid solution taken in a conical flask is titrated against NaOH from a burette using phenolphthalein indicator. The volume of NaOH required for the appearance of permanent faint pink color is tabulated below for five experiments. What is the concentration, in molarity, of the NaOH solution?

Volume of NaOH used in five titrations.
Answer and worked solution

Official answer: 0.11

The concordant titre is 9.0 mL (three identical readings; the first two are rough).

Oxalic acid is dibasic, so moles of NaOH = 2 × moles of acid:
M×9.0=2×0.10×5.00  ⟹  M=1.009.0=0.111 M.M\times9.0=2\times0.10\times5.00\implies M=\frac{1.00}{9.0}=0.111\text{ M}.
Answer: 0.11

Topics:Indicators and titrationsEquivalent concept and normality
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