No, nitric acid is significantly stronger than nitrous acid.
Nitric acid (HNO₃) is a powerful mineral acid, while nitrous acid (HNO₂) is a weaker, unstable acid. The difference in their strength stems primarily from the stability of their respective conjugate bases, which is directly related to how effectively the negative charge can be delocalized.
Understanding Acid Strength
Acid strength is determined by an acid's ability to donate a proton (H⁺). A stronger acid readily donates its proton, resulting in a more stable conjugate base. Conversely, a weaker acid holds onto its proton more tightly, forming a less stable conjugate base. This stability is often enhanced by factors such as resonance, where a negative charge can be spread out over multiple atoms.
Why Nitric Acid is Stronger Than Nitrous Acid
The superior strength of nitric acid can be attributed to the greater stability of its conjugate base compared to that of nitrous acid.
Conjugate Base Stability
- Nitric acid dissociates to form the nitrate ion (NO₃⁻).
- Nitrous acid dissociates to form the nitrite ion (NO₂⁻).
The nitrate ion is significantly more stable than the nitrite ion. This enhanced stability of the nitrate ion makes nitric acid a much stronger proton donor.
Resonance and Charge Delocalization
The key factor contributing to the greater stability of the nitrate ion is its ability to effectively delocalize the negative charge through resonance:
- Nitrate ion (NO₃⁻): In the nitrate ion, the excessive negative charge is spread out over three oxygen atoms. This extensive delocalization of charge across more atoms through resonance makes the nitrate ion highly stable.
- Nitrite ion (NO₂⁻): In contrast, the nitrite ion can only spread its excessive negative charge over two oxygen atoms. With fewer atoms to delocalize the charge, the nitrite ion is less stable than the nitrate ion.
A more stable conjugate base means the acid is more willing to lose its proton, hence nitric acid is a stronger acid.
Key Differences: Nitric Acid vs. Nitrous Acid
Here's a comparison highlighting their fundamental differences:
| Feature | Nitric Acid (HNO₃) | Nitrous Acid (HNO₂) |
|---|---|---|
| Acid Strength | Strong Acid (pKa ≈ -1.4) | Weak Acid (pKa ≈ 3.3) |
| Conjugate Base | Nitrate ion (NO₃⁻) | Nitrite ion (NO₂⁻) |
| Stability of Conjugate Base | Highly stable due to charge delocalization over 3 oxygen atoms. | Less stable due to charge delocalization over 2 oxygen atoms. |
| Stability of Acid | Stable liquid, strong oxidizing agent. | Unstable, usually prepared in situ; decomposes easily. |
| Oxidizing Power | Very strong oxidizing agent. | Moderate oxidizing and reducing agent. |
| Common Uses | Fertilizers, explosives, synthesis of organic compounds. | Used in the synthesis of diazonium salts, sometimes as a food preservative (in the form of nitrites). |
- For further reading on Nitric Acid, visit Wikipedia.
- For more information on Nitrous Acid, refer to Wikipedia.
- To understand acid strength and pKa, see Acid dissociation constant.
Practical Implications
The significant difference in strength between nitric acid and nitrous acid has major implications in various chemical reactions and industrial applications. Nitric acid's robust acidity and strong oxidizing properties make it indispensable in industries ranging from agriculture (fertilizers) to defense (explosives). Nitrous acid, being weaker and less stable, has more specialized applications, particularly in organic synthesis reactions such as diazotization.
