a) Cr2O3
Cr2O3 + 6NaOH + 3H2O → 2Na3[Cr(OH)6]
Cr2O3 + 6Na+ + 6OH- + 3H2O → 6Na+ + 2[Cr(OH)6]3-
Cr2O3 + 6HCl → 2CrCl3 + 3H2O
Cr2O3 + 6H+ + 6Cl- → 2Cr3+ + 6Cl- + 3H2O
b) CuO
CuO + 2NaOH + H2O → Na2[Cu(OH)4]
CuO + 2Na+ + 2OH- + H2O → 2Na+ + [Cu(OH)4]2-
CuO + 2HCl → CuCl2 + H2O
CuO + 2H+ + 2Cl- → Cu2+ + 2Cl- + H2O
c) As2O3
As2O3 + 6NaOH → 2Na3AsO3 + 3H2O
As2O3 + 6Na+ + 6OH- → 6Na+ + 2AsO33+ + 3H2O
As2O3 + 6HCl → 2AsCl3 + 3H2O
As2O3 + 6H+ + 6Cl- → 2As3+ + 6Cl- + 3H2O
d) SnO
SnO + 2NaOH + H2O → Na2[Sn(OH)4]
SnO + 2Na+ + 2OH- + H2O → 2Na+ + [Sn(OH)4]2-
SnO + 2HCl → SnCl2 + H2O
SnO + 2H+ + 2Cl- → Sn2+ + 2Cl- + H2O
