[Rutherford]

Why KAl(SO4)2, NaHSO4, NaH2PO4 make acidic solutions? I know protolysis, but I cant' understand these three examples.

[AWK]

http://en.wikipedia.org/wiki/Br%C3%B8nsted%E2%80%93Lowry_acid%E2%80%93base_theory

[Rutherford]

I know that theory, but I don't understand why those compounds make an acidic solution.
KAl(SO₄)₂-->?
NaHSO₄ made from a strong base (NaOH) and a strong acid (HSO₄^-) so it has to make a neutral solution.
NaH₂PO₄ same as above only that the H₂PO4^- acid is less strong than HSO4^- so it should make a basic solution, but they are all acidic.

[Borek]

NaHSO₄ made from a strong base (NaOH) and a strong acid (HSO₄^-) so it has to make a neutral solution.

HSO₄^- is not the acid used to prepare NaHSO₄.

[Rutherford]

H₂SO₄?

[AWK]

All: Al(H₂O)₆³⁺, HSO₄^- and H₂PO₄^- are Bronsted acids.

[Rutherford]

How does that explain my question? Sorry for bothering, but I really don't understand. After a lot of thinking I came to this: using NaHSO4 for example, if I write the hydrolysis reaction:
Na⁺+H⁺+SO₄^2-+H₂O-->Na⁺+SO₄^2-+H₃O⁺
The H₃O⁺ makes the solution acidic.
NaH₂PO₄ i can't write the H2PO4^- anion as 2H⁺+PO4^3- because it is a weak acid:
Na⁺+H₂PO₄^-+H₂O-->Na⁺+HPO₄^-+H₃O⁺ but why isn't here H3PO4 and OH^- made when H₂PO₄^- can be a proton donor and acceptor either and the Ka1 of H3PO4 isn't too big like it is for H₂SO₄? And what would the hydrolysis reaction for KAl(SO₄)₂ look like?

[Borek]

Na⁺+H⁺+SO₄^2-+H₂O-->Na⁺+SO₄^2-+H₃O⁺

This is not hydrolysis. HSO₄^- is an acid, that's enough. Na⁺ presence doesn't matter.

i can't write the H2PO4^- anion as 2H⁺+PO4^3- because it is a weak acid:

It is a weak acid, but still strong enough to acidify the solution. Again, Na⁺ presence doesn't matter.

And what would the hydrolysis reaction for KAl(SO₄)₂ look like?

Al case is a different one.

[AWK]

http://www.mpilkington.com/Lecture_21.pdf

http://www.docbrown.info/page07/appendixtrans01.htm

http://www.chemicalforums.com/index.php?topic=17016.0

[Rutherford]

You are right Borek, I should remove the Na⁺ ions because they are on the both side of the equations. How do I know if an acid is strong or weak, what pKa is the limit value?
And pretty much I have to read now because of AWK. Thanks to you both!