Understanding Acid-Base Conjugates and Salt Hydrolysis
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Conjugate Acid-Base Pairs
The CN⁻ ion is a base because it is capable of accepting a proton to form HCN, its conjugate acid:
CN⁻ + H₂O ⇌ HCN + OH⁻
The NH₄⁺ ion is an acid because it is capable of yielding a proton to form NH₃, its conjugate base:
NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺
The SO₄²⁻ ion is a base because it is capable of accepting a proton to form the HSO₄⁻ ion, its conjugate acid:
SO₄²⁻ + H₂O ⇌ HSO₄⁻ + OH⁻
Salt Hydrolysis and Solution pH
Potassium Chloride (KCl)
, is a salt that dissociates in aqueous solution leading to potassium ions (K +) and ions
chloride (Cl?). The chloride ion (Cl?) comes from a strong acid such as hydrochloric acid (HCl) and therefore it is
a weak conjugate base that is not capable of reacting with water. Cl? + H2O reacts not
For its part, the potassium ion comes from a strong base such as potassium hydroxide (KOH) and therefore will be an acid
conjugate weak that it is capable of reacting with water. K + + H2O reacts not
Thus the hydrolysis will not occur and thus the resulting solution will have a neutral character.
a) Ammonium nitrate (NH4NO3) is a salt that dissociates in aqueous solution leading to the ammonium ion (NH4 +)
and nitrate (NO3). The chloride ion (NO3) comes from a strong acid such as hydrochloric acid (HNO3) and therefore is a
weak conjugate base that is not capable of reacting with water. NO3 + H2O? No Reacts
For its part, the ammonium ion (NH4 +) comes from a weak base such as ammonia (NH3) and therefore is a
conjugate acid stronger than if it can react with water. NH4 + + H2O? NH3 + H3O +
Therefore we can say that salt water solution is acid in nature, and that in solution
H3 O + ion would Finally the aqueous solution of sodium acetate (CH3COONa) would lead to the presence of ions in solution
acetate (CH3 - COO?) and sodium ions (Na +). The acetate ion derived from acetic acid (CH3COOH) is a weak acid and therefore is a base
strong conjugate is capable of reacting with water. CH3COO? + H3O +? CH3COOH + OH
For its part, the sodium ion as we have seen is a weak conjugate acid does not react with water.
Na + + H2 O No reactions resulting in the dissolution OH ions are present? and therefore we can say that winding
have basic character.