Determine if the pH < 7 or pH > 7 (at 25 °C) for aqueous solutions of the following salts:
0) MnBr2
1) Cr(NO3)3
2) NiI2
3) Cu(ClO4)2
4) CoCl2
5) NaHSO4
6) NaH2PO4
7) Na2HPO4
8) Na3PO4
9) Na2HAsO4
Show all the relevant chemical reactions that take place in the solution.
0) MnBr2
MnBr2(aq) → Mn2+(aq) + 2 Br–(aq)
Mn2+(aq) + 2 H2O(l) → ← MnOH+(aq) + H3O+(aq)
Br–(aq) + H2O(l) → NR
pH < 7
1) Cr(NO3)3
Cr(NO3)3(aq) → Cr3+(aq) + 3 NO3–(aq)
Cr3+(aq) + 2 H2O(l) → ← CrOH2+(aq) + H3O+(aq)
NO3–(aq) + H2O(l) → NR
pH < 7
2) NiI2
NiI2(aq) → Ni2+(aq) + 2 I–(aq)
Ni2+(aq) + 2 H2O(l) → ← NiOH+(aq) + H3O+(aq)
I–(aq) + H2O(l) → NR
pH < 7
3) Cu(ClO4)2
Cu(ClO4)2(aq) → Cu2+(aq) + 2 ClO4–(aq)
Cu2+(aq) + 2 H2O(l) → ← CuOH+(aq) + H3O+(aq)
ClO4–(aq) + H2O(l) → NR
pH < 7
4) CoCl2
CoCl2(aq) → Co2+(aq) + 2 Cl–(aq)
Co2+(aq) + 2 H2O(l) → ← CoOH+(aq) + H3O+(aq)
Cl–(aq) + H2O(l) → NR
pH < 7
5) NaHSO4
NaHSO4(aq) → Na+(aq) + HSO4–(aq)
Na+(aq) + 2 H2O(l) → NR
HSO4–(aq) + H2O(l) → ← H3O+(aq) + SO42–(aq)
pH < 7
6) NaH2PO4
NaH2PO4(aq) → Na+(aq) + H2PO4–(aq)
Na+(aq) + 2 H2O(l) → NR
H2PO4–(aq) + H2O(l) → ← H3PO4(aq) + OH–(aq) Kb = 1.0×10–14/7.1×10–3 = 1.4×10–12
OR
H2PO4–(aq) + H2O(l) → ← H3O+(aq) + HPO42–(aq) Ka = 6.3×10–8
pH < 7 since Kb < Ka
7) Na2HPO4
Na2HPO4(aq) → 2 Na+(aq) + HPO42–(aq)
Na+(aq) + 2 H2O(l) → NR
HPO42–(aq) + H2O(l) → ← H2PO4–(aq) + OH–(aq) Kb = 1.0×10–14/6.3×10–8 = 1.6×10–7
OR
HPO42–(aq) + H2O(l) → ← PO43–(aq) + H3O+(aq) Ka = 4.2×10–13
pH > 7 since Kb > Ka
8) Na3PO4
Na3PO4 → 3 Na+(aq) + PO43–(aq)
Na+(aq) + 2 H2O(l) → NR
PO43–(aq) + H2O(l) → ← HPO42–(aq) + OH–(aq)
pH > 7
9) Na2HAsO4
Na2HAsO4(aq) → 2 Na+(aq) + HAsO42–(aq)
Na+(aq) + 2 H2O(l) → NR
HAsO42–(aq) + H2O(l) → ← H2AsO4–(aq) + OH–(aq) Kb = 1.0×10–14/1.0×10–7 = 1.0×10–7
OR
HAsO42–(aq) + H2O(l) → ← AsO43–(aq) + H3O+(aq) Ka = 3.2×10–12
pH > 7 since Kb > Ka