The conjugate base of H2SO4 (sulfuric acid) is HSO4- (hydrogen sulfate ion).
Understanding Conjugate Acids and Bases
In chemistry, particularly within the Brønsted-Lowry acid-base theory, an acid is defined as a proton (H+) donor, and a base is a proton acceptor. When an acid donates a proton, the species remaining is its conjugate base. Conversely, when a base accepts a proton, the new species formed is its conjugate acid.
This relationship can be illustrated by the following general reaction:
Acid + Base ⇌ Conjugate Base + Conjugate Acid
For sulfuric acid (H2SO4), it acts as an acid by donating a proton. When H2SO4 loses one proton (H+), it forms the hydrogen sulfate ion (HSO4-). Therefore, HSO4- is the conjugate base of H2SO4.
The Dissociation of Sulfuric Acid
Sulfuric acid is a strong acid that undergoes dissociation in water. Its first dissociation step is virtually complete:
H2SO4(aq) + H2O(l) → HSO4-(aq) + H3O+(aq)
In this reaction:
- H2SO4 acts as the acid, donating a proton to water.
- H2O acts as the base, accepting the proton.
- HSO4- is the conjugate base of H2SO4.
- H3O+ (hydronium ion) is the conjugate acid of H2O.
Characteristics of HSO4-
The hydrogen sulfate ion (HSO4-) itself can also act as an acid, though it is a weaker acid than H2SO4. This means it can donate a second proton:
HSO4-(aq) + H2O(l) ⇌ SO4^2-(aq) + H3O+(aq)
In this second dissociation step:
- HSO4- acts as an acid, donating a proton.
- SO4^2- (sulfate ion) is the conjugate base of HSO4-.
This property of being able to both donate and accept protons makes HSO4- an amphiprotic species.
Common Acid-Conjugate Base Pairs
Understanding the concept of conjugate pairs is fundamental in acid-base chemistry. Here are a few more examples:
| Acid (Proton Donor) | Conjugate Base (Acid minus H+) |
|---|---|
| H2SO4 | HSO4- |
| HCl (Hydrochloric acid) | Cl- (Chloride ion) |
| HNO3 (Nitric acid) | NO3- (Nitrate ion) |
| CH3COOH (Acetic acid) | CH3COO- (Acetate ion) |
| H2O (Water) | OH- (Hydroxide ion) |
| NH4+ (Ammonium ion) | NH3 (Ammonia) |
For further reading on acid-base theories and conjugate pairs, you can explore resources on Brønsted-Lowry acid-base theory.
