Hydrolizing salts?

Question

NaCl and Na2SO4 are non hydrolizing salts
NaCO3 and NaHCO3 are hydrolizing salts
the latter makes the pH higher in soils than the non hydrolizing ones.
Why is that?And where do those hydrolizing salts come from?

Answer 1

Actually, Na2SO4 is a hydrolyzing salt. The reaction is:

SO4= + H2O ---> HSO4- + OH-

If you dissolve Na2SO4 in water, it will turn phenolphthalein red and litmus paper blue. (Try it!) People sometimes don't realize that sulfuric acid is only a strong acid for the first proton, H2SO4 ---> H+ + HSO4-. For the second proton, HSO4- ---> H+ + SO4=, it's a weak acid.

For CO3= + H2O ---> HCO3- + OH-. phenolphthalein turns bright red. For HCO3- + H2O ---> H2CO3 + OH-, phenolphthalein turns faint pink.

Just remember: The salt of a strong acid and a strong base does not hydrolyze. The salt of a strong acid and a weak base hydrolyzes to a slightly acid solution. The salt of a weak acid and a strong base hydrolyzes to give a weakly basic(alkaline) solution.

Answer 2

hydrolysis is due to weak cation or anion which itself comes from weak acid or base NaCl is formed from strong acid and strong base so it does not hydrolyze while Na2CO3 and NaHCO3 are made weak acis and strong base so the anion is weak hence it hydrolyze