Sodium Carbonate cannot be used in place of (NH_4)_2 CO_3 for the identification of Ca^ 2+ , Ba^ 2+ and Sr^ 2+ ions (in group V ) during mixture analysis because :

Correct answer: A. Mg^ 2+ ions will also be precipitated. If Na_2 CO_3 is used in place of (NH_4)_2 CO_3 . It will precipitate group V radicals as well as magnesium radicals. The reason for this is the high ionization of Na_2 CO_3 in water into Na^ + and CO_3^ -- . Now the higher concentration of CO_3^ -- is available which exceeds the solubility product of group V radicals as well as that of magnesium radicals.

JEE Main 20139 AprilOnline

Exam: JEE Main
Year: 2013
Date: 9 April
Mode: Online
Subject: Chemistry
Chapter: s Block Elements

JEE Main 2013 · 9 April · Online · Chemistry · s Block Elements

Sodium Carbonate cannot be used in place of (NH_4)_2 CO_3 for the...

Sodium Carbonate cannot be used in place of

\left(\mathrm{NH}_4\right)_2 \mathrm{CO}_3

for the identification of

\mathrm{Ca}^{2+}, \mathrm{Ba}^{2+} and \mathrm{Sr}^{2+}

ions (in group

\mathrm{V}

) during mixture analysis because :

Options

A $\mathrm{Mg}^{2+}$ ions will also be precipitated.
BConcentration of $\mathrm{CO}_3{ }^{2-}$ ions is very low.
CSodium ions will react with acid radicals.
D $\mathrm{Na}^{+}$ ions will interfere with the detection of $\mathrm{Ca}^{2+}, \mathrm{Ba}^{2+}, \mathrm{Sr}^{2+}$ ions.

Correct answer

A. $\mathrm{Mg}^{2+}$ ions will also be precipitated.

Step-by-step solution

\mathrm{Na}_2 \mathrm{CO}_3

is used in place of \left(\mathrm{NH}_4\right)_2 \mathrm{CO}_3

. It will precipitate group

\mathrm{V}

radicals as well as magnesium radicals. The reason for this is the high ionization of

\mathrm{Na}_2 \mathrm{CO}_3

in water into

\mathrm{Na}^{+}

and

\mathrm{CO}_3^{--}

. Now the higher concentration of

\mathrm{CO}_3^{--}

is available which exceeds the solubility product of group

\mathrm{V}$ radicals as well as that of magnesium radicals.

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