[noiseordinance]

Hi there,

I'm trying to wrap my brain around how to predict reactions. I'm supposed to predict the pH of certain reactions and I'm having a hard time determining the net ionic, which is usually vital for determining pH, K_a, etc.

Here's an example of one that fooled me earlier:

NH₄Cl_(aq) + H₂O_(l)

Originally, I predicted that the Cl would be a mere spectator ion, leaving NH₄ to donate one of it's H atoms to convert H₂O to H₃O⁺. Instead, I'm finding that the reaction turns out to produce HCl + NH₄OH.

After seeing what the reaction should have been, I had an "oh duh" sorta moment. But I'm trying to figure out how to predict when the salt ionizes and remains as a spectator (often like it does in some of the buffer reactions) and when it instead forms an acid or base.

Are there any pointers that anyone can provide?

Thanks for you time!

[Borek]

Originally, I predicted that the Cl would be a mere spectator ion, leaving NH₄ to donate one of it's H atoms to convert H₂O to H₃O⁺.

And you were right.

[noiseordinance]

Hehe, well that's what I get for going with the first answer I saw on Yahoo that opposed my initial answer. However, I'm still curious... both scenarios seem possible to me, just depending on where H goes. How does one know what the reaction will produce?

[Borek]

You have to compare acid dissociation constants. You may safely assume that anions produced during dissociation of strong acids (like HCl) don't get protonated in water at all.

[enahs]

Generally, without any outside influence acid base reactions proceed in a manner to produce a weaker acid and base pair. Do you know of many acids stronger then HCl?