Understanding the Strength of Acids: Sulfuric Acid vs. Selenic Acid

Which is the stronger acid, H₂SO₄ or H₂SeO₄? Why?

Final answer:

Sulfuric acid (H₂SO₄) is stronger than selenic acid (H₂SeO₄) because sulfur is more electronegative than selenium, which stabilizes the charge on the conjugate base, making the acid stronger.

Explanation:

The strength of an acid in oxyacids, where the central atoms have the same oxidation number, is dependent on the electronegativity of the central atom. Since sulfur (S) is more electronegative than selenium (Se), sulfuric acid (H₂SO₄) is the stronger acid compared to selenic acid (H₂SeO₄). This higher electronegativity leads to better stabilization of the negative charge in the conjugate base, making the acid more prone to lose its proton (H+).

When comparing the acidity of sulfuric acid (H₂SO₄) and selenic acid (H₂SeO₄), it is important to consider the chemical properties of sulfur and selenium. Sulfur is known to be more electronegative than selenium in the periodic table. Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond.

Due to the higher electronegativity of sulfur compared to selenium, sulfuric acid exhibits stronger acidic properties. The increased electronegativity of sulfur results in better stabilization of the negative charge in the conjugate base that forms after the acid donates a proton (H+). This enhanced stability of the conjugate base makes sulfuric acid more willing to dissociate and release protons, leading to its higher acidity compared to selenic acid.

Additionally, another factor that contributes to the acidity of oxyacids is the size of the central atom. In this case, sulfur has a larger atomic size compared to selenium. However, in oxyacids with central atoms of the same oxidation state, electronegativity plays a more significant role in determining acid strength than atomic size.

In conclusion, sulfuric acid is the stronger acid between H₂SO₄ and H₂SeO₄ due to sulfur's higher electronegativity, which stabilizes the charge on its conjugate base, ultimately leading to greater acidity. By understanding the relationship between electronegativity and acid strength, we can explain why certain acids exhibit more pronounced acidic properties than others.