Analytical ChemistryHard

Question

Nitrite (NO2-) interferes in the ′ring-test′ of nitrate (NO3-). Some  of the following reagents can be used for the removal of nitrite.
I : Potassium dichromate (s)
II : CO(NH2)2 (urea).
III : NH2SO3 H (sulphamic acid)
IV : Zinc /sodium hydroxide

Options

A.I, II
B.I, II, IV
C.II, III
D.II, III, IV

Solution

(I) Cr2O72- + 8H+ + 3NO2- → 2Cr3+  + 3NO3- + 4H2O.
(II) CO(NH2)2 + 2HNO2 → 2N2↑ ­ + CO2 ­ ↑ + 3H2O.
(III) HOSO2.NH2 + HNO2 →   N2↑ ­ + 2H+ + SO42- + H2O.
(IV) NO2- and NO3- both on reduction with Zn/NaOH on warming gives ammonia gas.

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