Seriously need help with an AP Chemistry problem.

I need to solve this by tomorrow, and I cannot find any sort of suggestion on how to solve this in my book, notes, other examples, or even online. I've been stressing over this for at least an hour now...

"To what final concentration of NH₃ must a solution be adjusted to just dissolve 0.020 mol of NiC₂O₄ (K_sp = 4 X 10^-10) in 1.0 L of solution? [Hint: you can neglect the hydrolysis of C₂O₄^2- because the solution will be quite basic.]"

I am really, really desperate now. I don't need a simple answer, I need to know how to even do this. I have no clue where to start.

edited 10th Feb '11 8:50:03 PM by Anomalocaris20

You cannot firmly grasp the true form of Squidward's technique!

It's been a while since AP Chemistry, but I might be able to take a shot at this.

The goal, from what I can tell, is to get all the nickel into solution. From the solubility product, you know what concentration of oxalate you need for that to happen. Unfortunately, simply dissociating the oxalate will result in a far higher concentration of it that we want.

But oxalate is a weak base. By protonating it, we can turn the oxalate ions into hydrogenoxalate ions  ^*

, which don't factor into the solubility product. From hydrogenoxalate's Ka, we can determine the resulting concentration of Hydronium.

At this point, we can almost get the concentration of ammonia from its Ka. But it seems like we would still need the concentration of ammonium.

EDIT: Hmm, perhaps not. The above suggests a preposterously high concentration of hydronium. Is there any more information given about the problem?

edited 10th Feb '11 8:25:49 PM by petrie911

Belief or disbelief rests with you.

Oh god. Don't tell me this is the kind of stuff I'll be taking next year.

I was looking forward to Chemistry...I'm good in math but still...

"Who wants to hear about good stuff when the bottom of the abyss of human failure that you know doesn't exist is so much greater?"-Wraith

If I knew the reaction equation, I could probably at least check your math.

edited 10th Feb '11 8:37:32 PM by Pykrete

Nope. That's it. It's also the only homework problem in the whole chapter like this, and there are no examples in the text or notes. Real nice of my teacher to assign it, huh?

Regular Chem is much easier than this.

The problem is that I have no math. I literally have no idea how to begin this problem.

edited 10th Feb '11 8:48:51 PM by Anomalocaris20

You cannot firmly grasp the true form of Squidward's technique!

Well, I'm not sure what to say then. We've got about 5 potentially relevant reactions

Ni C₂O₄ <=> Ni⁺² + C₂O₄^-2 (Ksp = 4*10^-10)

C₂O₄^-2 + H₃O⁺ <=> HC₂O₄^- + H₂O (pKa = 4.28)

HC₂O₄^- + H₃O⁺ <=> H₂C₂O₄ + H₂O (pKa = 1.27)

NH₃ + H₃O⁺ <=> NH₄⁺ + H₂O (pKa = 9.21)

H₃O⁺ + OH^- <=> 2H₂O (pKw = 14)

And basically you need to get these into some sort of equilibrium where [Ni] = .02M, keeping in mind the concentrations are all bound by the rules above.

edited 10th Feb '11 9:34:07 PM by petrie911

Belief or disbelief rests with you.