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Compounds that should not be used as primary standards in titrimetric analysis are A. \({\mathrm{Na}}_{2}{\mathrm{Cr}}_{…

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Compounds that should not be used as primary standards in titrimetric analysis are

A. \({\mathrm{Na}}_{2}{\mathrm{Cr}}_{2}{\mathrm{O}}_{7}\)
B. Oxalic acid
C. \(\mathrm{NaOH}\)
D. \({\mathrm{FeSO}}_{4}\cdot 6{\mathrm{H}}_{2}\mathrm{O}\)
E. Sodium tetraborate

Choose the most appropriate answer from the options given below:

[JEE Main 2025, 3 Apr (Shift 2)]

a

B and D Only

b

D and E Only

c

C, D and E Only

d

A, C and D Only

✓ Correct answer: d)

A, C and D Only

Explanation

A primary standard is a highly pure, stable compound with a known and exact composition that can be accurately weighed and dissolved to prepare a solution of known concentration.

  • NaOH is hygroscopic, so it cannot be used as a primary standard.

  • \({\mathrm{FeSO}}_{4}\cdot 6{\mathrm{H}}_{2}\mathrm{O}\) is unstable and easily oxidised, so it cannot be used.

  • \({\mathrm{Na}}_{2}{\mathrm{Cr}}_{2}{\mathrm{O}}_{7}\) is hygroscopic, so it cannot be used.

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