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Shriver & Atkins: Inorganic Chemistry 4e

Chapter 13

Acidity of aqueous carbon dioxide
A lump of solid carbon dioxide is placed in water containing a few drops of universal indicator. The indicator changes colour to indicate an acid.

CO2(g) + H2O(l) ↔ H3O+(aq) + H3O-(aq)

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Disproportionation of the hydrogen carbonate ion
The hydrogen carbonate ion is in equilibrium with the carbonate ion in a disproportionation reaction:

HCO3-(aq) + HCO3-(aq) ↔ CO32-(aq) + H2O(l) + CO2(aq)

Calcium ion (small, high charge) forms insoluble calcium carbonate (high lattice energy as carbonate is high charge also). Thus addition of calcium ion consumes the carbonate ion and the equilibrium shifts right to replenish the carbonate ion. The process continues until almost all of the hydrogen carbonate ion has been consumed.

Ca2+ (aq) + CO32-(aq) → CaCO3(s)

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Reaction of carbonates with acid
Addition of any strong acid to a carbonate or hydrogen carbonate will give a release of carbon dioxide gas. The production of the gas can be illustrated by damp blue litmus paper turning red.

HCO3-(aq) + H+ (aq) → H2O(l) + CO2(g)

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Reaction of lead(II) ion with hydroxide ion
Lead is another amphoteric metal. In this case, we show that addition of hydroxide ion to lead(II) ion initially gives a white precipitate of lead(II) hydroxide.

Pb2+(aq) + 2OH-(aq) → Pb(OH)2(s)

Addition of excess hydroxide ion results in the formation of the colorless soluble tetrahydroxolead(II) complex ion.

Pb(OH)2(s) + 2OH(aq) two-way arrow [Pb(OH)4]2-(aq)

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Reaction of lead(II) ion with iodide ion
 A characteristic test for lead(II) ion is the production of bright yellow lead(II) iodide:

Pb2+(aq) + 2I-(aq) → PbI2(s)

Addition of excess iodide ion results in the formation of the colorless soluble tetraiodoplumbate(II) complex ion.

PbI2(s) + 2I- (aq) two-way arrow [PbI4]2-(aq)

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