Weak and strong acids

Answer 1

There is no such acid which is both strong and weak. An acid is either weak or it is strong.

However, sulfuric acid as a diprotic acid is a strong acid in its first dissociation.

H2SO4 --> H+ + HSO4-

and is a weak acid in its second dissociation

HSO4- --> H+ + SO42-

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It is a strong acid only for the first hydrogen ion that is produced.

(1) H2SO4 --> H+ + HSO4^-

The remaining bisulfate ion, HSO4^-, is a weak acid and only partially dissociates.

(2) HSO4^- <==> H+ + SO4^2-

A misconception is that since sulfuric acid is a strong acid, that it dissociates like this:

(3) H2SO4 --> 2H+ + SO4^2-

That simply isn't the case except for extremely dilute solutions. As the concentration of the acid decreases, the acid behaves more and more like a strong diporotic acid. At "infinite dilution" it is accurate to write the dissociation as equation (3).

Read more: http://wiki.answers.com/Q/Is H2SO4 a strong acid or weak acid#ixzz2TQB85UJp

Answer 2

A strong acid disassociates completely or nearly completely when diluted with water. A weak acid will not disassociate completely, or even hardly at all.

For example, if you have a strong acid solution, such as hydrochloric acid (HCl - a strong acid) and add baking soda, (sodium carbonate), the free hydrogen ions (the H in the HCl) in the solution will bind with the carbonate portion of the sodium carbonate to make Carbonic Acid - a weak acid. Carbonic Acid is weak, so it binds the ions, and lowers the acidity of the solution. The Sodium and Chlorine form table salt, if the solution is dried.

The idea here is that the carbonic acid does not completely disassociate in the water - in other words, the hydrogen ion does not separate from the carbonate in water - maybe only 10% will disassociate. HCl is another matter - it's a very strong acid, where 100% of the molecules dissassociate.

Answer 3

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