Which of the following can behave as Bronsted-Lowry bases in aqueous solution? H2PO4- NaOH I- HF None of the Above
The correct answer and explanation is:
The correct answer is: H₂PO₄⁻, NaOH, and I⁻
Explanation:
The Brønsted-Lowry definition of acids and bases focuses on proton (H⁺) transfer:
- A Brønsted-Lowry acid is a proton donor.
- A Brønsted-Lowry base is a proton acceptor.
In aqueous solution, a substance behaves as a Brønsted-Lowry base if it can accept a proton (H⁺) from water or other proton donors.
Let’s analyze each compound:
1. H₂PO₄⁻ (Dihydrogen phosphate ion):
This is the conjugate base of H₃PO₄ (phosphoric acid) and can act as both an acid and a base (amphiprotic).
It can accept a proton to form H₃PO₄, making it a Brønsted-Lowry base in the presence of a stronger acid.
✅ Can behave as a Brønsted-Lowry base
2. NaOH (Sodium hydroxide):
NaOH dissociates in water to form Na⁺ and OH⁻.
The hydroxide ion (OH⁻) is a strong Brønsted-Lowry base because it readily accepts H⁺ to form water (H₂O).
✅ Can behave as a Brønsted-Lowry base (via OH⁻)
3. I⁻ (Iodide ion):
I⁻ is the conjugate base of HI (hydroiodic acid), a strong acid.
Though it is a very weak base, it still can accept a proton, so it qualifies under the Brønsted-Lowry definition.
✅ Can behave as a Brønsted-Lowry base
4. HF (Hydrofluoric acid):
HF is a weak acid; it tends to donate protons rather than accept them.
Therefore, HF acts as a Brønsted-Lowry acid, not a base.
❌ Cannot behave as a Brønsted-Lowry base
Conclusion:
The species that can act as Brønsted-Lowry bases in aqueous solution are:
- H₂PO₄⁻
- NaOH (via OH⁻)
- I⁻
So the correct answer is:
👉 H₂PO₄⁻, NaOH, and I⁻