How do you know if these solutions are acidic, basic, or nearly neutral?

Question

a. NH4NO2
b. Cr(NO3)3

Answer 1

Hydrolyze salts to make that determination.
NH4NO2 + HOH ==> HNO2 + NH4OH
Note that HNO2 is a weak acid and NH4OH actually is NH3 + H2O (a weak base); therefore, the decision rests upon which is stronger, the weak acid or the weak base. The (H^+) of solutions of salts that are salts of weak acids AND weak bases = sqrt(KwKa/Kb). Look up Ka and Kb, substitute, convert H to pH and you have your answer. OR, just pH = pKw + pKa - pKb. (P. S. I don't see this question much--this formula was taught to me when I took analytical chemistry but I don't see it much in books anymore). Fortunately I still remember it after 60 years.

The second one is simpler.
Cr(NO3)3 + 3HOH ==> Cr(OH)3 + 3HNO3
Cr(OH)3 is a weak base. HNO3 is a strong acid; therefore, the solution will be acidic.
All of this type question hinges on how the hydrolysis equation looks. I suggest you write them even though you think neither anion nor cation is hydrolyzed.
Here are examples of the four types.
NaCl + HOH ==> NaOH + HCl
NaOH is strong base, HCl a strong acid, solution is neutral

NH4Cl + HOH ==> NH4OH + HCl
NH4OH (NH3 + HOH) is a weak base, HCl a strong acid, solution is acidic.

NaC2H3O2 (sodium acetate).
NaAc + HOH ==> NaOH + HAc.
NaOH is a strong base, HAc a weak acid, solution is basic.

NH4Ac + HOH ==> NH4OH + HAc
Kb NH3 = 1.8 x 10^-5
Ka HAc = 1.8 x 10^-5
(H^+) = (KwKa/Kb). Since Ka = Kb soln is neutral. If Ka is stronger soln is acid. If Kb is stronger, soln is basic.

Answer 2

How can i get Factor of 1.666 for multipling to Mn