Page 13 - Pharmaceutical analytical chemistry |

• Although H2O is one of the products in most neutralization reactions,

the reaction of an acid with the base NH3 provides a prominent

exception.

* H2SO4 (aq) + 2 NH3 (aq) ⎯→ (NH4)2 SO4 (aq)

acid base salt

then

H+ (aq) + NH3 (aq) ⎯→ NH4+ (aq)

• Acids may be monoprotic (only one acidic H atom per acid
molecule) e.g. HCl & HNO3, or polyprotic (yielding 2 or more acidic
hydrogens per molecule) e.g. H3PO4.
H3PO4 + NaOH ⎯→ NaH2PO4 + H2O
H3PO4 + 2NaOH ⎯→ Na2HPO4 + 2H2O
H3PO4 + 3NaOH ⎯→ Na3PO4 + 3H2O

5. Acid base reactions with gas formation

Certain salts, notably CO32-, SO32- and S2- react with acids to form a
gaseous product. The resulting reaction is considered an exchange, or
metathesis, reaction.

Na2CO3 + 2HCl ⎯→ 2NaCl + H2O + CO2
Na2SO3 + 2HCl ⎯→ 2NaCl + H2O + SO2

Na2S + 2HCl ⎯→ 2NaCl + H2S

6. Amphoterism

Amphoterism, in chemistry, is the reactivity of a substance with both
acids and bases, acting as an acid in the presence of a base and as a base
in the presence of an acid. Water is an example of an amphoteric
substance.

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