Why is it that in some acids, hydrogen ions are "given up" (so to speak) more easily than in others. I've noted that it occurs particularly in diprotic acids (such as H2SO4). Where the first part of the reaction is always complete (100% ionisation), and the second half is incomplete (or at least not likely to be complete unless the sulfuric acid solution is extremely diluted). Thanks :)
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Basically (teehee) the answer of why some acids are stronger than others comes down to electronegativity and electron density.
That is, if the electron density in an acid molecule is more concentrated in one area, it will be easier for that acid to lose a proton.
Consider hypochlorous acid and perchloric acid
HClO - Ka = 2.9x10^-8
HClO4 - Ka = very very very large
Basically HClO4 is polarized much more towards the oxygens due to their "hogging" of the electrons, whereas HClO has a much more even electron density distribution.
The second part of your question has a lot to do with the collision theory of chemical kinetics.
H2SO4 ---> H+ + HSO4-
This dissociation, like you said, takes place with easy. The reason that this dissociation:
HSO4- ----> H+ + SO4-2
does not take place until extreme dilution is because of molecular interactions. Ions are bumping into each other, thus reforming HSO4- many times as a result of H+ ions bumping into the SO4-2 ions in the solution.
If you dilute a solution, you also increase its volume. When the volume is increased, less of this bumping occurs, and thus more SO4-2 can exist in solution as a result of an increased amount of space where it will not collide with an H+ ion to reform HSO4-.
That is, if the electron density in an acid molecule is more concentrated in one area, it will be easier for that acid to lose a proton.
Consider hypochlorous acid and perchloric acid
HClO - Ka = 2.9x10^-8
HClO4 - Ka = very very very large
Basically HClO4 is polarized much more towards the oxygens due to their "hogging" of the electrons, whereas HClO has a much more even electron density distribution.
The second part of your question has a lot to do with the collision theory of chemical kinetics.
H2SO4 ---> H+ + HSO4-
This dissociation, like you said, takes place with easy. The reason that this dissociation:
HSO4- ----> H+ + SO4-2
does not take place until extreme dilution is because of molecular interactions. Ions are bumping into each other, thus reforming HSO4- many times as a result of H+ ions bumping into the SO4-2 ions in the solution.
If you dilute a solution, you also increase its volume. When the volume is increased, less of this bumping occurs, and thus more SO4-2 can exist in solution as a result of an increased amount of space where it will not collide with an H+ ion to reform HSO4-.