Salt Hydrolysis: Ion Classification, Amphiprotic Salts, and Metal-Ion Acidity

All flashcards

Salt hydrolysis

A reaction between a dissolved salt ion and water that can change the solution’s pH.

Amphiprotic ion

An ion that can both donate and accept a proton.

Hydrated metal-ion acidity

A metal ion polarizes coordinated water’s O–H bonds, making proton transfer more likely.

Common-ion effect in metal-ion hydrolysis

Added hydronium suppresses further acid ionization by shifting the hydrolysis equilibrium.

Polyprotic species

A species that can donate more than one proton in successive ionization steps.

Quiz questions

1. Ammonium fluoride has $K_a(\mathrm{NH_4^+})=5.6\times10^{-10}$ and $K_b(\mathrm{F^-})=1.6\times10^{-11}$. Assuming comparable concentrations, what is the solution’s acid–base character?Answer: Acidic, because the ammonium ion’s acidic effect is stronger.
2. Why can hydrated aluminum ions make water acidic?Answer: The metal ion polarizes coordinated water’s O–H bonds, promoting proton transfer.
3. What happens to hydrated metal-ion hydrolysis when strong acid adds hydronium to the solution?Answer: Hydronium suppresses further hydrolysis because it is a product of the equilibrium.
4. Bicarbonate has $K_a=4.7\times10^{-11}$ and $K_b=2.3\times10^{-8}$. Which behavior predominates in water?Answer: Basic behavior, because its proton-accepting tendency is stronger.
5. What is the expected acid–base character of a potassium carbonate solution in the introductory salt-ion classification?Answer: Basic, because carbonate is a basic anion and potassium is effectively inert.