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Answer the following in brief :The aqueous solution of sodium carbonate is alkaline whereas the aqueous solution of ammonium chloride is acidic. Explain. - Chemistry

Answer in Brief

Answer the following in brief :

The aqueous solution of sodium carbonate is alkaline whereas the aqueous solution of ammonium chloride is acidic. Explain.

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Solution

i. Sodium carbonate (Na2CO3) is a salt of weak acid H2CO3 and strong base NaOH. When dissolved in water, it dissociates completely.

\[\ce{Na2CO3_{(aq)} -> 2Na^+_{ (aq)} + CO^2-_{3(aq)}}\]

ii. The Na+ ions of salt have no tendency to react with OH ions of water since the possible product of the reaction is NaOH, a strong electrolyte.

iii. On the other hand, the reaction of `"CO"_3^{2-}` ions of salt with the H3O+ ions from water produces unionized H2CO3.

\[\ce{CO^{2-}_{3{(aq)}} + 2H2O_{(l)} ⇌   H2CO_{3(aq)} + 2OH^-_{ (aq)}}\]

Thus, the hydrolytic equilibrium for Na2CO3 is,

\[\ce{Na2CO_{3(aq)} + H2O_{(l)} ⇌ H2CO_{3(aq)} + 2Na^+_{ (aq)} + 2OH^-_{ (aq)}}\]

iv. As a result of excess OH ions produced, the resulting solution of Na2CO3 is alkaline.

v. Similarly, ammonium chloride (NH4Cl) is salt of strong acid HCl and weak base NH4OH. When NH4Cl is dissolved in water, it dissociates completely as,

\[\ce{NH4Cl_{(aq)} -> NH^+_{4(aq)} + Cl^-_{ (aq)}}\]

vi. `"Cl"_{("aq")}^-` ions of salt have no tendency to react with water because the possible product HCl is a strong electrolyte.

vii. The reaction of `" NH"_4^+` ions with OH ions form unionized NH4OH. The hydrolytic equilibrium for NH4Cl is then written as,

\[\ce{NH^+_{4(aq)} + 2H2O_{(l)} ⇌ NH4OH_{(aq)} + H3O+_{ (aq)}}\]

viii. Due to the presence of an excess of H3O+ ions, the resulting solution of NH4Cl is acidic.

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APPEARS IN

Balbharati Chemistry 12th Standard HSC Maharashtra State Board
Chapter 3 Ionic Equilibria
Exercise | Q 3.08 | Page 62
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