JEE Main 2016 · Chemistry · Qualitative and Practical Chemistry · easy

A white water-soluble salt imparts a brick-red colour to the flame, gives a brown ring when its solution is mixed with freshly prepared FeSO4 and…

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A white water-soluble salt imparts a brick-red colour to the flame, gives a brown ring when its solution is mixed with freshly prepared

\mathrm{FeSO_4}

and conc.

\mathrm{H_2SO_4}

is run down the side of the tube, and gives a white precipitate with

\mathrm{(NH_4)_2C_2O_4}

but none with dilute

\mathrm{H_2SO_4}

. The salt is

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Answer: (A) $\mathrm{Ca(NO_3)_2}$

The brown ring test is specific for nitrate (formation of

[\mathrm{Fe(H_2O)_5NO}]^{2+}

), which excludes

\mathrm{CaCl_2}

. A brick-red flame indicates calcium; strontium gives crimson red and barium apple green. Ammonium oxalate precipitates calcium oxalate, but

\mathrm{Sr^{2+}}

and

\mathrm{Ba^{2+}}

would also form sulphate precipitates with dilute

\mathrm{H_2SO_4}

, whereas

\mathrm{CaSO_4}

is soluble enough (

K_{sp}\approx 10^{-5}

) not to precipitate from dilute solution. Hence

\mathrm{Ca(NO_3)_2}

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