Chemistry: Which is more acidic?

1. Feb 26, 2012

Bipolarity

1. The problem statement, all variables and given/known data

Which is more acidic, and why?
$$H_{2}SO_{4}$$
$$H_{2}SeO_{4}$$

2. Relevant equations

3. The attempt at a solution
Because Se is larger, it has a weaker Coulomb force with the H atoms. So it will more readily give up the protons of the H atoms. Hence it should be more acidic, but turns out sulphuric acid is more acidic?

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BiP

2. Feb 26, 2012

chiddler

The general trend for oxyacids is as follows:

1. The more oxygen that is present, the more acidic the compound is. This is because more oxygens allow more resonance stability.

2. The more electronegative the central atom is, the more acidic it is. This is due to inductive effect where the oxygens that donate a proton are stablized by the central atom that can absorb some of the electron density and stabilize the conjugate base.