[Vicktor]

I understand most of what I am supposed to be doing, but there are a few things that stand out. I will post the whole problem, just so I don't accidentally leave something critical out.

A 1.00 liter solution is made up of .23M ammonia and .25M Ammonium Chloride. If .12 moles of HBr is added to the system...(and it goes on to name T/F questions.)

Chemical Equation: NH₃+H₂O  NH₄⁺ + OH^-

I need help understanding a few concepts as to why certain parts be as they are.

In one explanation, the homework states "The equilibrium H₃O will increase, because [OH] = Kb[NH₃] / [NH₄⁺]. Since the concentration of NH₃ decreased and the concentration of [NH₄⁺] increased, the concentration [OH^-] at equilibrium is lower.[/b]

Why is it that they have written the equation as [Reactants] / [Products] instead of vice versa? I have yet to go over this in class, it is on my online homework. But, I have no idea where this came about.

Can anyone lend me some of your insight on this subject, It would be greatly appreciated.

-Thank you, Vicktor.

[Borek]

Chemical Equation: NH₃+H₂O  NH₄⁺ + OH^-

While this is correct in general, it doesn't describe what is happening in the solution after the acid was added:

NH₃ + H⁺ NH₄⁺

(and which is IMHO more important here)

[OH] = Kb[NH₃] / [NH₄⁺]

That's just wrong, most likely a mistake during editing/formatting, it should be

[tex][OH^-] = \frac {K_b[NH_4^+]}{[NH_3]}[/tex]

[Vicktor]

Borek, I completely agree. This is from the OWL website for Chemistry students. This is not the same exact problem in which I initially posted about, but the same question still arises. This is the explination portion of why the answers are what they are, according to OWL. Does this clarify anything for you or is your opinion still the same?

Thank you, Vicktor.

[Borek]

I am not sure what you are referring to, but this particular part is OK - it is about Ka, not about Kb, and the equation posted is correct.

[Vicktor]

This one in the screen shot is about Ka, yes, but the original one I posted was Kb.

My question is why is the equation they give, the [H₃O⁺] = Ka[HF]/[F^-] instead of Ka[F^-]/[HF]?

It would see to me that it should still be [Products]/[Reactants] even if this were referring to the H-H equation which states [A^-]/[HA]

[Borek]

By definition

[tex]K_a = \frac {[H^+][F^-]}{[HF]}[/tex]

solving for H⁺:

[tex][H^+] = \frac {K_a[HF]}{[F^-]}[/tex]

it is a basic algebra.

[Vicktor]

OF COURSE! I am sorry for such stupidity on my part. I am having trouble connecting the dots between older material and newly learned material. I guess lack of sleep can do this to you haha. I appreciate the clarification, though. So easy.