SATHEE: Formulas to Remember

Formulas to Remember

Additional Ionic Equilibrium Formulae and Equations

Dissociation of Water:

$H_{2} O ⇌ H^{+} + O H^{-}$ $K_{w} = [H^{+}] [O H^{-}] = 1.0 \times 10^{- 14} at 25 ° C$

Autoionization of Water:

$2 H_{2} O ⇌ H_{3} O^{+} + O H^{-}$ $K_{a u t o} = [H_{3} O^{+}] [O H^{-}] = 1.0 \times 10^{- 14} at 25 ° C$

Hydrolysis of Salts:

$S a l t + H_{2} O ⇌ A c i d + B a s e$ $K_{h} = \frac{[H_{3} O^{+}] [B a s e]}{[S a l t]}$

Common Ion Effect:

The presence of a common ion in a solution decreases the dissociation of a weak acid or base.

$H A ⇌ H^{+} + A^{-}$ $K_{a} = \frac{[H^{+}] [A^{-}]}{[H A]}$

If a salt containing the anion (A^- ) is added to the solution, the equilibrium will shift to the left, decreasing the concentration of (H^+) and (A^- ) and increasing the concentration of (HA).

The Henderson-Hasselbalch Equation:

For an acid-base pair (HA/A^- ),

$p H = p K a + l o g \frac{[A^{-}]}{[H A]}$

This equation can be used to calculate the pH of a buffer solution or to determine the concentration of an acid or base in a solution.

Buffer Solutions:

A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. Buffer solutions are made up of a weak acid and its conjugate base, or a weak base and its conjugate acid.

The buffer capacity of a solution is the amount of acid or base that can be added to the solution without causing a significant change in pH.

Polyprotic Acids:

Polyprotic acids are acids that can donate more than one proton. The ionization of polyprotic acids follows a stepwise process, with each proton dissociation having its own Ka value.

Amphoteric Substances:

Amphoteric substances are substances that can act as both acids and bases. The ionization of amphoteric substances depends on the pH of the solution.

Formulas to Remember