Question

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Nitrogen dioxide (NO2) gas and bromine (Br2) gas both are brown in colour. How will you
distinguish between them ?
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Answer 1

For Br2 - add Br2 to liquid alkene , the bromine decolourises. For NO2 -There is no simple relatively unambiguous test. So just check for bromine and other one is NO2.

In my knowledge there are two (there could be definitely more ways) decent ways of distinguishing chemically→

Starch paper

Starch Iodide paper ( this one's might be a bit ambiguous)

Starch paper →

Br2 forms a orange-red spot on the paper due to the formation of a complex with the natural polymer (Starch) whereas NO2 doesn't do so.

Starch Iodide paper→

Here we use the fact that NO2 is a better oxidiser compared to Br2.

An oxidiser can form a blue-black spot on the paper due to the formation of a complex of (I3)- ions with the polymer.

(I3)- ions appears from the redox reaction….

I- + oxidiser →(I3)-

Now being a better oxidiser NO2 forms the spot immediately whereas Br2 takes time thereby helping us distinguish between them.

Answer 2

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Pas.s the gas through freshly prepared ferrous sulphate solution (FeSO4) . If it turns black brown the ,gas is Nitrogen dioxide (NO2) otherwise Bromine (Br2) gas .

$\huge\purple{Hope \: it \: helps❤}$