Simulation · Chemistry · Class 11
Why some salt solutions are not neutral
From the lesson Common ion effect and hydrolysis of salts in Equilibrium. Change the values and watch what happens.
Why some salt solutions are not neutralChemistry · Class 11
The idea behind it
NCERT § "Common Ion Effect in the Ionization of Acids and Bases"; § "Hydrolysis of Salts and the pH of their Solutions"
- Adding an ion already present in a weak electrolyte's equilibrium pushes the equilibrium back and suppresses ionisation; adding CH₃COONa to acetic acid lowers [H₃O⁺] and raises pH.
- The common ion effect is a direct application of Le Chatelier's principle.
- Salts of a strong acid and a strong base (NaCl) do not hydrolyse and give neutral solutions.
- Salts of a weak acid and a strong base (CH₃COONa) hydrolyse to give basic solutions.
- Salts of a strong acid and a weak base (NH₄Cl) hydrolyse to give acidic solutions.
- For a salt of a weak acid and a weak base (CH₃COONH₄), pH = 7 + ½(pKa − pKb); the solution is neutral only if pKa = pKb.
- Hydrolysis is the reaction of a salt's cation or anion (or both) with water, which changes the pH away from 7.