Chemistry Reference
In-Depth Information
Answers:
A. F-
B. NO
3
-
C. HSO
4
-
D. NH
3
The procedure for the next example is exactly the opposite. The conju-
gate acid of a base is the substance that is left behind after the base has
gained a proton. Remember to add both the H and the + to each sub-
stance, and then check your answers.
Example 2
What would be the conjugate acid for each of the following bases?
A. OH
-
B. H
2
O
C. NH
2
-
D. NH
3
Adding an H and a +1 charge to each substance, OH
-
becomes H
2
O;
H
2
O becomes H
3
O
+
; NH
2
-
becomes NH
3
; and NH
3
becomes NH
4
+
. Again,
write out an equation that is balanced for atoms and for charge, if you
don't see one of these answers. For example:
NH
2
-
+ H
+
NH
3
Answers:
A. H
2
O
B. H
3
O
+
C. NH
3
D. NH
4
+
Another common type of question is shown in Example 3.
Example 3
Identify the two conjugate acid-base pairs shown in this equation:
HCl + NH
3
NH
4
+
Cl
-
This question should be easy enough to solve, provided that you recall
the definition of a conjugate acid-base pair. A conjugate acid-base pair is a
pair of substances that differ from each other by a single (H
+
) proton.
Clearly, when HCl donates a single proton, it becomes Cl
-
. That makes
HCl and Cl
-
our first conjugate acid-base pair. When NH
3
accepts a pro-
ton, it becomes NH
4
+
, making them our second conjugate acid-base pair.
Answer:
The two conjugate acid-base pairs are (HCl and Cl
-
) and
(NH
3
and NH
4
+
).
