There is p pi -d pi dative bonding in H3PO4 and its depronated forms which some e- density from O p-orbitals can donate to vacant P d-orbitals, therefore, O is less basic. While As d-orbitals 4d are higher in energy so that this dative bonding is not quite favour. This is unrelated to direct bonds. Its not a binary acid.
Borek Mr. For the same electronegativity think about radius of central atom in the acid group. ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations. Sc Biomedical Sciences, Utrecht University. Quote from: dnbwise on July 26, , PM. GCT Guest. Acid strength depends on the charge separation of the electronegative atom and hydrogen in facilitating the positive charge character on the hydrogen and thus the energy for such the acid base reaction and inversely on the bond strength, both are somewhat dependeent on electronegativity.
You need to reread your text, I really don't know where you got those rules of thumb mentioned in the op After you reread your text on the strength of acids you should be able to understand why phosphoric acid is the stronger acid.
My text reads as follows: the strength of an acid depends on its ability to donate a proton. Two factors determine how easily a proton is released from a binary non-metal hydride: 1. Across a period, non-metal hydride acid strength increases. Down a group, non-metal hydride acid strength increases. For oxoacids: 1. For oxoacids with the same number of oxygens around E the central nonmetal , acid strength increases with the electronegativity of E.
For oxoacids with a different number of oxygen atoms around E, acid strength increases with the number of O atoms. IF they had an even number of electonegative atoms bonded to the central atom and equal or even closely similar number of terminal not bonded to H oxygens When you have binary acids bonded to one other anion With oxoacids like this first compare which one has more electronegative atoms Sign up to join this community.
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Viewed 8k times. Improve this question. Mathew Mahindaratne Parth Chauhan Parth Chauhan 4 4 silver badges 12 12 bronze badges. This is because the electrons are slightly withdrawn from the OH bond as the electronegativity of the central atom increases.
As bonding electrons are pulled closer to the OH bond, the molecule becomes more polar, and so the molecule becomes a stronger acid. Wikipedia's values for the pKa1, pKa2 and Ka3 of phosphoric acid are 2. For arsenic acid the values are 2. Consider the pka2 and pKa3 values I find the electronegativity argument dubious. Add a comment. Active Oldest Votes. Improve this answer. Jen Jen 1.
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