Name:
KEY
Conjugate Pairs Practice #2
An acid is defined as a proton (H+) donor while a base is a proton acceptor. The substance that
is produced after an acid has donated its proton is called the conjugate base while the substance
formed when a base accepts a proton is called the conjugate acid. The conjugate acid can donate a
proton to the conjugate base, to reform the original reactants in the reverse reaction.
HF + H2O  H3O+ + FAcid
Base
c. acid c. base
In the reaction above, HF is the acid and H2O is the base. The HF has given a proton to the H2O,
forming H3O+ and F-. Since the product H3O+ can donate a proton back to F- it is labeled the conjugate
acid, while the F- is the conjugate base.
Example
Write an equation that shows NH3 reacting with HCl. Label the acid, base, and conjugate acid and
H+
conjugate base.
-Write reactants and transfer a proton from the acid to the base: NH3 + HCl  NH4+ + ClBase
Acid
c. acid
Identify the acid, base, the conjugate acid, and the conjugate base in each of the equations.
1. HCl + NH3  NH4+ + ClA
B
AC
CB
2. OH + HCN  H2O + CNB
A
CA
CB
3. PO43- + HNO3  NO3- + HPO42B
A
CA
CB
4. HCO3- + HCl  H2CO3 + ClB
A
CA
CB
5. HCO3 + OH  H2O + CO32A
B
CA
CB
6. NH4+ + H2O  NH3 + H3O+
A
B
CB
CA
7. C2O42- + HC2H3O2  HC2O4- + C2H3O2B
A
CA
CB
28. HPO4 + H2O  OH + H2PO4
B
A
CB
CA
9. HClO4 + H2O  H3O+ + ClO4–
A
B
CA
CB
+
10. H2SO3 + H2O  H3O + HSO3–
A
B
CA
CB
+
11. HC2H3O2 + H2O  H3O + C2H3O2–
A
B
CA
CB
+
–
12. H2S + H2O  H3O + HS
A
B
CA CB
13. HSO3– + H2O  H3O+ + SO32–
A
B
CA
CB
+
14. NH3 + H2O  NH4 + OH–
B
A
CA
CB
–
–
15. HF + HSO3  F + H2SO3
A
B
CB CA
–
16. HNO2 + HS  NO2– + H2S
A
B
CB
CA
c. base
Fill in the following table.
Acid
Base
17
HNO2
H2O
Conjugate Acid
H3O+
Conjugate Base
NO2-
Equation
HNO2 + H2O  NO2- + H3O+
18
H2O
F-
HF
OH-
H2O + F  HF + OH-
19
HCN
NH3
NH4+
CN-
NH3 + HCN  NH4+ + CN-
20
HClO3
H3O+
H2O
ClO3-
HClO3 + H3O+  H2O + ClO3-
21
HSO4-
PO43-
HPO42-
SO42-
HSO4 + PO43-  HPO42- + SO42-
22
H2O
S2-
HS-
OH-
S2- + H2O  OH- + HS-
23
HCO2H
OH-
H2O
CO2H+
HCO2H + OH-  H2O + CO2H+
24. Write an equation that shows the reaction of ammonia, NH3, with hydrobromic acid, HBr. Label
the acid, the base, the conjugate acid, and the conjugate base.
NH3 + HBr  Br- + NH4
B
A
CB
CA
25. Write an equation that shows the reaction of phosphate ion, PO43–, reacting with hydronium
ion, H3O+. Label the acid, the base, the conjugate acid, and the conjugate base.
H3O+ + PO43-  H2O + HPO42A
B
CB
CA
26. Write an equation that shows the reaction of hydrogen sulfide, HS– with hydroxide ion, OH–.
Label the acid, the base, the conjugate acid, and the conjugate base.
HS- + OH-  H2O + S2A
B
CA
CB