Barrons SAT Subject Test Chemistry, 13th Edition

The silver ions combine with the chloride ions to form an insoluble

precipitate, silver chloride. If the reaction had been like this:

(K+ + Cl−) + (Na+ + NO 3 −) → K+ + NO 3 − + Na+ + Cl−

merely a mixture of the ions would have been shown in the final

solution.

2. Another reason for a reaction of this type to go to completion is the
   formation of a nonionizing product such as water. This weak electrolyte
   keeps its component ions in molecular form and thus eliminates the
   possibility of reversing the reaction. All neutralization reactions are of this
   type.

(H+ + Cl−) + (Na+ + OH−) → H 2 O (l) + Na+ + Cl−

This example shows the ions of the reactants, hydrochloric acid and

sodium hydroxide, and the nonelectrolyte product water with sodium

and chloride ions in solution. Since the water does not ionize to any

extent, the reverse reaction cannot occur.

The third reason for double displacement to occur is the evolution of

a gaseous product. An example of this is calcium carbonate reacting

with hydrochloric acid:

CaCO 3 (s) + 2HCl(aq) → CaCl 2 (aq) + H 2 O(l) + CO 2 (g)

3. Another example of a compound that evolves a gas in sodium sulfite with
   an acid is:

Na 2 SO 3 (aq) + 2HCl(aq) → 2NaCl(aq) + H 2 O(l) + SO 2 (g)

In general, acids with carbonates or sulfites are good examples of this

type of equation.

Hydrolysis Reactions

Hydrolysis reactions are the opposite of neutralization reactions. In hydrolysis the
salt and water react to form an acid and a base. For example, if sodium chloride
is placed in solution, this reaction occurs to some degree:

(Na+ + Cl−) + H 2 O(l) → (Na+ + OH−) + (H+ + Cl−)