If yes, check to see if there are changes in oxidation numbers. If so, this is an oxidation/reduction reaction. Use the rules for oxidation/reduction reactions.
a. How do we recognize acids?
i. H is written first in the chemical formula. The common strong acids: nitric acid (HNO3); hydrochloric acid (HCl); hydrobromic acid (HBr); hydriodic acid (HI); perchloric acid (HClO4); sulfuric acid (H2SO4, first hydrogen only).
ii. Most cations (the exceptions: cations from strong bases).
iii. Organic acids with chemical formulas written as RCOOH or RCO2H.
b. How do we recognize bases?
i. Metal hydroxides. Group 1 (LiOH, NaOH, KOH, RbOH, and CsOH) and Group 2 (Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2) hydroxides are considered strong bases.
ii. Most anions (the exceptions: anions from strong acids).
iii. Amines, which are organic compounds having a nitrogen with an available lone pair, generally written as RN, RNH, or RNH2.
Use the Brønsted-Lowry definition and transfer an H+ ion from the acid to the base.
If the base contains hydroxide ion, OH–, then one of the products is water, H2O(l).
The stoichiometry must be adjusted for each individual reaction.
If a strong acid or strong base is involved, the acid/base reaction will go to completion. If only weak species are present, a calculation using Ka and Kb must be done to determine the extent of reaction, but generally this will be written as an equilibrium.
Acid/base reactions often create ionic salts as products. Check to see if any ionic salts can precipitate.
If so, write the dissolution reaction (or reactions, if more than one salt is present) that generates the ions in solution.
a. Is water written as a reactant?
If water is written explicitly as a reactant, check for possible hydrolysis reactions with the cation and the anion. Hydrolysis reactions are always equilbria.
b. Look for cation-anion combinations.
See if a cation present in solution can combine with an anion present in solution to form a precipitate. Precipitation reactions go to completion.
c. Is there a common ligand present?
Common ligands include ammonia (NH3), ethylenediammine (en, H2NCH2CH2NH2), cyanide (CN–), oxalate (ox2–, C2O42–), thiocyanate (SCN–), and ethylenediamminetetracetate (EDTA4–). Halides and hydroxides can also act as ligands.
If a common ligand is present and a cation, this may be a complex ion formation reaction (Lewis acid/base). Check the table of complex ions to see if this combination of cation and ligand do form a complex ion and, if so, to determine the stoichiometry.
1. HBr(aq) + NH3(aq)
HBr is a strong acid and NH3 is a weak base, so this is an acid-base reaction.
HBr(aq) + NH3(aq) → NH4+(aq) + Br–(aq)
2. H3PO4(aq) + F–(aq)
H3PO4 is a weak acid and F– is a weak base so this is an acid-base reaction.
H3PO4(aq) + F–(aq) → ← H2PO4–(aq) + HF(aq)
3. Fe(NO3)2(aq) + H2O(l)
Fe(NO3)2 is a soluble ionic salt so dissociate it into the constituent ions.
Fe(NO3)2(aq) → Fe2+(aq) + 2 NO3–(aq)
Fe2+(aq) is the cation of a weak base so will hydrolyze but NO3– is the anion of a strong acid so will not hydrolyze.
Fe2+(aq) + 2 H2O(l) → ← FeOH+(aq) + H3O+(aq)
4. NaF(aq) + H2O(l)
NaF is a soluble ionic salt so dissociate it into the constituent ions.
NaF(aq) → Na+(aq) + F–(aq)
Na+(aq) is the cation of a strong base so will not hydrolyze but F– is the anion of a weak acid so will hydrolyze.
F–(aq) + H2O(l) → ← HF(aq) + OH–(aq)
5. ZnF2(aq) + H2O(l)
ZnF2 is not on the list of compounds with a Ksp so we can assume that it is soluble.
ZnF2(s) → Zn2+(aq) + 2 F–(aq)
Both of these ions are hydrolyzable.
Zn2+(aq) + 2 H2O(l) → ← ZnOH+(aq) + H3O+(aq) Ka = 2.5×10–10
F–(aq) + H2O(l) → ← HF(aq) + OH–(aq) Kb = 1.0×10–14/6.6×10–4 = 1.5×10–11
Since Ka > Kb, acid hydrolysis predominates.
6. Pb(NO3)2(aq) + K2SO4(aq)
Both of these are soluble salts so write the solubilization reactions.
Pb(NO3)2(aq) → Pb2+(aq) + 2 NO3–(aq)
K2SO4(aq) → 2 K+(aq) + SO42–(aq)
Lead sulfate is a sparingly soluble salt, so precipitation will occur.
Pb(NO3)2(aq) + K2SO4(aq) → PbSO4(s) + 2 K+(aq) + 2 NO3–(aq)
7. Fe(NO3)3(aq) + CsCl(aq)
Both of these are soluble salts so write the solubilization reactions.
Fe(NO3)3(aq) → Fe3+(aq) + 3 NO3–(aq)
CsCl(aq) → Cs+(aq) + Cl–(aq)
No combination of ions leads to a precipitate.
Fe(NO3)3(aq) + CsCl(aq) → Fe3+(aq) + 3 NO3–(aq) + Cs+(aq) + Cl–(aq)
8. Co(NO3)2(aq) + H2S(aq)
Cobalt nitrate is a soluble salt and hydrosulfuric acid is a diprotic weak acid.
Co(NO3)2(aq) → Co2+(aq) + 2 NO3–(aq)
H2S(aq) + H2O(l) → ← H3O+(aq) + HS–(aq)
HS–(aq) + H2O(l) → ← H3O+(aq) + S2–(aq)
Cobalt sulfide is a sparingly soluble salt.
Co(NO3)2(aq) + H2S(aq) + 2 H2O(l) → CoS(s) + 2 H3O+(aq) + 2 NO3–(aq)
9. Ca(NO3)2(aq) + K2SO4(aq)
Both of these are soluble salts so write the solubilization reactions.
Ca(NO3)2(aq) → Ca2+(aq) + 2 NO3–(aq)
K2SO4(aq) → 2 K+(aq) + SO42–(aq)
Calcium sulfate is a sparingly soluble salt, so precipitation will occur.
Ca(NO3)2(aq) + K2SO4(aq) → CaSO4(s) + 2 K+(aq) + 2 NO3–(aq)
10. CaHPO4(s) + HCl(aq)
CaHPO4 is a sparingly soluble salt.
CaHPO4(s) → ← Ca2+(aq) + HPO42–(aq)
HPO42– is a base that can accept two hydrogen ions and HCl is a strong acid.
CaHPO4(s) + 2 HCl(aq) → Ca2+(aq) + H3PO4(aq) + 2 Cl–(aq)
11. CaHPO4(s) + NaOH(aq)
CaHPO4 is a sparingly soluble salt.
CaHPO4(s) → ← Ca2+(aq) + HPO42–(aq)
HPO42– is a acid that can donate a hydrogen ions and NaOH is a strong base.
CaHPO4(s) + NaOH(aq) → Ca2+(aq) + PO43–(aq) + H2O(l) + Na+(aq)
Calcium phosphate and calcium hydroxide are both sparingly soluble salts so precipitation will occur. Since calcium phosphate is less soluble than calcium hydroxide, the phosphate salt precipitation will dominate.
3 CaHPO4(s) + 3 NaOH(aq) → Ca3(PO4)2(s) + 3 Na+(aq) + PO43–(aq) + 3 H2O(l)
12. Cu2+(aq) + NH3(aq)
Ammonia is a common ligand and examination of the Table of Complex Ion Formation Constants shows the reaction:
Cu2+(aq) + 4 NH3(aq) → ← [Cu(NH3)4]2+(aq)
13. Mg(s) + NO3–(aq) → Mg2+(aq) + NO2(g)
Products are given and there are oxidation state changes so this is a redox reaction.
Oxidation: Mg(s) → Mg2+(aq) + 2 e–
Reduction: 2×[ NO3–(aq) + 2 H+(aq) + e– → NO2(g) + H2O(l) ]
Net: Mg(s) + 2 NO3–(aq) + 4 H+(aq) → Mg2+(aq) + 2 NO2(g) + 2 H2O(l)
14. Cr2O72–(aq) + SO2(g) → Cr(OH)3(s) + SO42–(aq)
Products are given and there are oxidation state changes so this is a redox reaction. The chromium(III) hydroxide indicates that this reaction is done in base.
Oxidation: 3×[ SO2(g) + 2 H2O(l) → SO42–(aq) + 4 H+(aq) + 2 e– ]
Reduction: Cr2O72–(aq) + 8 H+(aq) + 6 e– → 2 Cr(OH)3(s) + H2O(l)
Net in acid: 3 SO2(g) + Cr2O72–(aq) + 5 H2O(l) → 2 Cr(OH)3(s) + 3 SO42–(aq) + 4 H+(aq)
Neutralization of the acid: 4×[ H+(aq) + OH–(aq) → H2O(l) ]
3 SO2(g) + Cr2O72–(aq) + H2O(l) + 4 OH–(aq) → 2 Cr(OH)3(s) + 3 SO42–(aq)
15. ClO2–(aq) → ClO–(aq) + ClO4–(aq)
Products are given and there are oxidation state changes so this is a redox reaction. However, this example can be balanced by inspection.
3 ClO2–(aq) → 2 ClO–(aq) + ClO4–(aq)
Clicking on the number will open a new tab with the answer.
1. NaOH(aq) + H2SO4(aq)
2. Co(OH)2(s) + HCl(aq)
3. Mn(OH)2(s) + HClO4(aq)
4. KNO2(aq) + H2O(l)
5. CsF(aq) + HNO3(aq)
6. H3BO3(aq) + H2O(l)
7. CH3NH2(aq) + H2O(l)
8. Ni(NO3)2(aq) + H2O(l)
9. CoCl2(aq) + H2O(l)
10. Al(OH)3(s) + HI(aq)
11. HCl(aq) + H2O(l)
12. HNO3(aq) + Ca(OH)2(aq)
13. NH3(aq) + HBr(aq)
14. HC2H3O2(aq) + RbOH(aq)
15. Ba(OH)2(s) + HCN(aq)
16. H2S(aq) + NaOH(aq)
17. CsOH(aq) + NH4Cl(aq)
18. HClO4(aq) + CH3NH2(aq)
19. C5H5N(aq) + H2O(l)
20. C5H5N(aq) + HCl(aq)
21. NiCl2(aq) + CuNO3(aq)
22. Pb(OH)2(s) + H2SO4(aq)
23. AgNO3(aq) + HCl(aq)
24. H3PO4(aq) + CaI2(aq)
25. NaF(aq) + Ba(NO3)2(aq)
26. H2S(aq) + CoBr2(aq)
27. Ca(OH)2(aq) + NiSO4(aq)
28. Mn(NO3)2(aq) + Na2CO3(aq)
29. Pb(NO3)2(aq) + KI(aq)
30. MgBr2(aq) + Na3AsO4(aq)
31. ZnCl2(aq) + K2S(aq)
32. HF(aq) + Ca(OH)2(aq)
33. Sr(NO3)2(aq) + K2CrO4(aq)
34. H2C2O4(aq) + MgCl2(aq)
35. AgNO3(aq) + NaC2H3O2(aq)
36. FeCl2(aq) + NaOH(aq)
37. Rb2CO3(aq) + Ca(NO3)2(aq)
38. H2S(aq) + ZnBr2(aq)
39. Cd(ClO4)2(aq) + Na2C2O4(aq)
40. Na2CrO4(aq) + Pb(C2H3O2)2(aq)
41. AgNO3(aq) + NaCN(aq)
42. CuCl2(aq) + NH3(aq)
43. NiSO4(aq) + NH3(aq)
44. AgCl(s) + NH3(aq)
45. Fe(NO3)3(aq) + KCN(aq)
46. ZnSO4(aq) + NH3(aq)
47. CdI2(aq) + NH3(aq)
48. Cu(NO3)2(aq) + RbCN(aq)
49. AgNO3(aq) + Na2S2O3(aq)
50. ZnSO4(aq) + KOH(aq)
51. HNO3(aq) + HI(aq) → NO(g) + I2(s)
52. Zn(s) + Cu(NO3)2(aq) → Zn2+(aq) + Cu(s) + NO3–(aq)
53. MnO4–(aq) + Br–(aq) → Mn2+(aq) + Br2(l) (pH = 1)
54. Cr2O72–(aq) + Cl–(aq) → Cr3+(aq) + Cl2(g) (pH = 1)
55. H2(g) + Zn(NO3)2(aq) → NO(g) + Zn2+(aq) (pH = 1)
56. NaClO(aq) + Zn(s) → Zn(OH)2(s) + Cl–(aq) + Na+(aq)
57. MgI2(aq) + Ag2CrO4(s) → I2(s) + Ag(s) + Mg2+(aq) + CrO42–(aq) (pH = 14)
58. CoCl2(aq) + Cd(s) → Cd2+(aq) + Co(s) + Cl –(aq)
59. AgCl(s) + H2C2O4(aq) → Ag(s) + CO2(g) + Cl –(aq)
60. Fe(CN)63–(aq) + N2H5+(aq) → Fe(CN)64–(aq) + N2(g) (pH = 1)
61. ClO3–(aq) → ClO4–(aq) + ClO2–(aq) (pH = 14)
62. F2(g) + Fe(s) → FeF3(s)
63. Li(s) + Sn4+(aq) → Li+(aq) + Sn(s)
64. O3(g) + Cu(s) → Cu2+(aq) + O2(g) (pH = 1)
65. S2O82–(aq) + Cr(s) →Cr3+(aq) + SO42–(aq) (pH = 1)
66. H2O2(aq) + Mn2+(aq) → MnO4–(aq) + H2O(l) (pH = 1)
67. MnO4–(aq) + H2C2O4(aq) → Mn2+(aq) + CO2(g)
68. Ce4+(aq) + Cu+(aq) → Ce3+(aq) + Cu2+(aq)
69. Co3+(aq) + Hg(l) → Co2+(aq) + Hg22+(aq) (pH = 1)
70. ClO2–(aq) + Fe(s) → Fe(OH)3(s) + ClO –(aq)
71. HF(aq) + Mg(OH)2(s)
72. NaCl(aq) + Hg2(NO3)2(aq)
73. C6H5NH2(aq) + H2O(l)
74. MnCl2(aq) + H2O(l)
75. K(s) + SnCl2(aq) → K+(aq) + Sn(s) + Cl –(aq) (pH = 1)
76. H2SO4(aq) + BaBr2(aq)
77. Ca(C2H3O2)2(aq) + H2O(l)
78. NH4ClO4(aq) + CsOH(aq)
79. H2SO3(aq) + H2O(l)
80. Mg(ClO4)2(aq) + Rb2CO3(aq)
81. H3AsO4(aq) + Pb2+(aq)
82. LiNO2(aq) + H2O(l)
83. H2O2(aq) + Al(s) → Al3+(aq) + H2O(l) (pH = 1)
84. HCN(aq) + Sr(OH)2(s)
85. Ni(NO3)2(aq) + NaCN(aq)
86. HF(aq) + NH3(aq)
87. PbO2(s) + Pb(s) → PbSO4(s) (pH = 1, sulfuric acid)
88. AgBr(s) + NH3(aq)
89. NaHSO4(aq) + Sr(NO3)2(aq)
90. Ca(s) + CrO42–(aq) → Cr(OH)3(s) + Ca2+(aq)
91. NH2CH2CH2NH2(aq) + H2O(l)
92. C6H5OH(aq) + H2O(l)
93. FeCl3(aq) + H2S(aq)
94. HC7H5O2(aq) + CsOH(aq)
95. MnO4–(aq) + Cr3+(aq) → Mn2+(aq) + Cr2O72–(aq) (pH = 1)
96. NH2CONH2(aq) + H2O(l)
97. NH2OH(aq) + H3AsO4(aq)
98. AgNO3(aq) + NaC2H3O2(aq)
99. Ca(ClO4)2(aq) + H2C2O4(aq)
100. C6H5OH(aq) + H2O(l)