Predicting Stronger Acid in Acid Pairs

Which acid is the stronger acid in the following pairs: (a) (H₂SO₃) or (H₂SeO₃) (b) (H₂SeO₄) or (H₂SeO₃) The strengths of the acids H₂SO₃, H₂SeO₄, and HSO₄− compared to their counterparts are stronger due to factors like electronegativity and the oxidation state of the central atom, which contribute to the ease of proton release or the stability of the conjugate base.

Explanation:

Predicting Acid Strength

When comparing acids for their strength, we often consider factors such as the elements present, their electronegativity, the stability of the conjugate base, and the oxidation state of the central atom in oxyacids.

H₂SO₃ (Sulfurous acid) vs. H₂SeO₃ (Selenous acid):

H₂SO₃ is a stronger acid because sulfur is more electronegative than selenium. This makes the release of protons easier from the acid, thereby increasing the acid strength.

H₂SeO₄ (Selenic acid) vs. H₂SeO₃ (Selenous acid):

Among these, H₂SeO₄ is the stronger acid because it is a more oxidized form, having one more oxygen atom than H₂SeO₃. This leads to greater delocalization of charge and a stronger acid.

HSO₄− (Hydrogen sulfate) vs. HSeO₄− (Hydrogen selenate):

HSO₄− is the stronger acid, because sulfur is more electronegative than selenium, making it better at stabilizing the negative charge on the conjugate base.

Note that these predictions are based on general trends in acid strength. In different conditions, such as varying solvent systems, the acid strengths might be different.

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