The pH of salts is determined by the hydrolysis. Therefore, the secret is knowing what the products are IF they hydrolyze. I have learned some fictitious reactions. It works as follows:
Salt of strong acid(SA) + strong base(SB) as in NaCl.
NaCl + HOH ==> NaOH + HCl
NaOH is a strong base; HCl is a srong acid. Neutral. Never mind that neither Cl^- nor Na^+ is hydrolyzed and that the reaction above doesn't exist. The result of neutral is correct.
Salt of SB + WA(weak acid)
NaAc(sodium acetate)
NaAc + HOH ==> NaOH + HAc(acetic acid)
NaOH is a strong base. HAc is weak
acid. basic.
(Note: Actually, the base part IS hydrolyzed as
Ac^- + HOH == HAc + OH- and you can see why it is basis --because of the release of OH^-.)
salt of WB and SA.
NH4Cl + HOH ==> NH3 + HCl + HOH
NH3 is a weak base. HCl is a strong acid. acid.
(Note: actually, the cation IS hydrolyzed as in
NH4^+ + H2O ==> H3O^+ + NH3 and you can see why it is acidic--because of the release of hydronium ion.)
salt of WA and WB
The pH depends upon which is the stronger. If both are about the same the soln will be neutral. If the acid is stronger it will be acidic; if the base is stronger it will be basic.
NH4Ac, (NH4)2C2O4, are two examples.
(Note: actually, both anion and cation are hydrolyzed as in
NH4Ac + HOH ==> NH4OH + HAc and the NH4OH technically exists as NH3 and H2O.)
Which salt below will dissolve in water to yield an acidic solution?
a) NaNO2
b) K C§¤O4
c) NH4NO3
d) Na2CO3
e) Mg Br2
help!
1 answer