The species: H2O, HCO3 –, HSO4 – and NH3 can act both as Brönsted acids and bases. For each case give the corresponding conjugate acid and base

In the realm of acid-base chemistry, understanding the behavior of substances like H2O, HCO3–, HSO4–, and NH3 is crucial. These species can indeed function as both Brønsted acids and bases, which means they can donate or accept protons (H+ ions). Let’s break down each species and identify their corresponding conjugate acids and bases.

Water (H2O)

Water is a fascinating substance because it can act as both an acid and a base. When it donates a proton, it acts as a Brønsted acid:

• As an acid: H2O → H+ + OH– (the conjugate base is OH–)

Conversely, when water accepts a proton, it behaves as a Brønsted base:

• As a base: H2O + H+ → H3O+ (the conjugate acid is H3O+)

Bicarbonate Ion (HCO3–)

The bicarbonate ion is another versatile species. It can donate a proton, functioning as an acid:

• As an acid: HCO3– → H+ + CO3^2– (the conjugate base is CO3^2–)

Alternatively, it can accept a proton, acting as a base:

• As a base: HCO3– + H+ → H2CO3 (the conjugate acid is H2CO3)

Hydrogen Sulfate Ion (HSO4–)

The hydrogen sulfate ion also exhibits dual behavior. When it donates a proton, it acts as an acid:

• As an acid: HSO4– → H+ + SO4^2– (the conjugate base is SO4^2–)

On the other hand, when it accepts a proton, it serves as a base:

• As a base: HSO4– + H+ → H2SO4 (the conjugate acid is H2SO4)

Ammonia (NH3)

Ammonia is well-known for its ability to act as a base. When it accepts a proton, it behaves as a Brønsted base:

• As a base: NH3 + H+ → NH4+ (the conjugate acid is NH4+)

However, ammonia can also act as an acid in certain reactions, although this is less common:

• As an acid: NH3 → NH2– + H+ (the conjugate base is NH2–)

Summary of Conjugate Pairs

To summarize, here are the conjugate acids and bases for each species:

• H2O: Conjugate acid: H3O+, Conjugate base: OH–
• HCO3–: Conjugate acid: H2CO3, Conjugate base: CO3^2–
• HSO4–: Conjugate acid: H2SO4, Conjugate base: SO4^2–
• NH3: Conjugate acid: NH4+, Conjugate base: NH2–

This dual behavior is a fundamental concept in acid-base chemistry, illustrating how substances can participate in various chemical reactions depending on the context. Understanding these relationships helps in predicting the outcomes of reactions and the behavior of different species in solution.