Chemistry, Third edition

6 · REACTIONS OF IONS IN SOLUTION

4. Reaction with carbonates and hydrogencarbonates

All acids react with carbonates to produce carbon dioxide gas. For example, the

ethanoic acid in vinegar will fizz with sodium carbonate. The reaction is

2CH 3 COOH(aq)Na 2 CO 3 (aq)2CH 3 COONa(aq)CO 2 (g)H 2 O(l)

ethanoic acid sodium ethanoate

in vinegar

The ionic equation for this reaction is

2H(aq)CO 32 (aq)CO 2 (g)H 2 O(l)

any acid carbonate ion

Hydrogencarbonates (also called bicarbonates) also fizz with acid:

H(aq)HCO 3 (aq)CO 2 (g)H 2 O(l)

hydrogencarbonate

ion

(Note that hydrogencarbonates decompose upon heatinggiving CO 2 (g):

2HCO 3 (aq)CO 2 (g)H 2 O(l)

The decomposition of solid sodium hydrogencarbonate (‘kitchen bicarb’) is utilized

in cooking, with the CO 2 gas causing cake mixtures to rise.)

5. Reaction with sulfites

Sulfites contain the ion SO 32 . (Don’t confuse this ion with the sulfate ion (SO 42 ),

which does not react with acids.) Acids react with sulfites making the sharp-smelling

gas sulfur dioxide (SO 2 ). The ionic equation is

SO 32 (aq)2H(aq)SO 2 (g)H 2 O(l)

sulfite ion

Hydrogensulfites (also called bisulfites) also react with acid:

H(aq)HSO 3 (aq)SO 2 (g)H 2 O(l)

hydrogensulfite

ion

6. Reaction with sulfides

The reaction of acids with sulfides (compounds containing the sulfide ion, S^2 ) pro-

duces the foul-smelling gas hydrogen sulfide – one of the products of rotten eggs.

The ionic equation for the reaction is

S^2 (s)2H(aq)H 2 S(g)

sulfide

ion

Metal ions often react with sulfide ions to produce insoluble sulfides. For

example,

Cu^2 (aq)S^2 (aq)CuS(s)

black

Sodium sulfide solution or hydrogen sulfide gas are used as the source of sulfide ions.

Solutions of Na, Ca^2  and K will not produce precipitates because their

sulfides are water soluble. Zinc sulfide (ZnS) is white, while lead(II) and silver

sulfides (PbS and Ag 2 S) are black.

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