Question

Explain the Hard/Soft Acids/Bases Principle - How to know which elements are soft or hard bases&acids?

Answer 1

Hard acid --> will dissociate completely i.e. 100%:

as follows:

HA --> H+ and A-

typically, the "A-" anion is a very electronegative material, which will have a higher tendency to leave the protons in solution

for a base...

the case is similar...

B + H2O --> BH+ + OH-

a strong base such as B, will attract H+ very strongly, so plenty of OH- will remeain in solution,

b)

Weak acid/bases

are those that will NOT dissocaite 100% so they will not be strong enough

HA <-> H+ + A-

with a K = [H+][A-]/[HA] value typically in the 10^-2 -- 10^-8 ranges