<p>Was the question "is the solution of Na3PO4 basic" or was it "Is Na3PO4 a base"?
Because the first one is F and the second one is T.
I thought it was the 1st one in the question, so I put F. It would be a shame if I misread.</p>
<p>wait, what is the Kb for PO4(3-)?</p>
<p>Hm. You know maybe I should apologize. I am doing the ICE table and the pH is definitely >7 so you might be right. Oh, man. I have to retake gen chem.</p>
<p>Martinibluex, no hard feelings, but as much as I respect a college premed, you have to check your facts:</p>
<p>You are adding Na3PO4 to H2O, not OH-, so, PO4(3-) is not competing against OH-, but H2O.
According to phosphate ion's Kb, which is 2.2 x 10-2, it is a much stronger base than H2O, whose Kb is 1.0 x 10 -7, so it will attract a H+ from water, not OH-, because it's making an OH-.
Think about it, why do other weak bases produce weak basic water solutions? If they were to compete with OH- as you say, then there would not be weak bases!</p>
<p>I think we should just stop arguing with each other...what's done is done...we can't change it...oh well, I just hope I did okay, meaning 750+</p>
<p>Just one more question please:
How did the question about NH4OH go exactly???</p>
<p>And also what is a competitive score? Does anyone know where to find the percentiles?</p>
<p>um...well....I thought NH4 and OH- would combine to produce NH3 and water in a water solution...but on second thought, NH4OH is also possible</p>
<p>I thought that too, but I just found this:
(1) NH3 + H2O <--> NH4+ + OH- ; Kb = 1.8 x 10-5</p>
<p>(2) H2O <--> H+ + OH- ; Kw = 1.0 x 10-14</p>
<p>Kb > Kw , therefore reaction 1 dominates </p>
<p>So I was wrong :/</p>
<p>Edit: another web site says that only 5% dissociates
So we might be right :))))</p>
<p>wait...do you remember the exact reaction for this question?</p>
<p>No, sorry I don't remember :/
Also, I put another edit above + I think they should compare Kb with 1/Kw because it goes H+ + OH-
Since 1/Kw is 10^14 I think that they would definitely recombine to form water and since NH3 is a gas it would keep escaping, meaning that according to LaCh... principles the reaction will go to completion because we are taking off the product constantly! Yes, I just got it - we are going to get NH3 and H2O!</p>
<p>that's good news...but are you sure?</p>
<p>I think so...
I thought that I was wrong because I used similar logic as I used in Na3PO4 (where I was wrong). However, here it is different. In the PO4 question I got confused because in O-chem my professor always went nuts whenever you use a synthesis reaction in which you make a start with a weaker base and you get a stronger one and PO4 3- is a weaker base than OH- so the equilibrium should be to the left. What I forgot to consider is that it is not all the way to the left (like with the escaping gaseous NH3) so there are OH- species and the pH>7.
In conclusion I think that you did good. I just went through your posts and I think that you got at most one wrong out of the questsions that you've discussed.</p>
<p>A conclusive proof on the NH4OH question!!!
"In other words,
the equilibrium NH3 + H2O = NH4+ + OH- lies decidedly to the left. Note
that there is no "NH4OH" in this solution. We should all stop referring to
"ammonium hydroxide" and "NH4OH". There is no evidence to suggest that
this exists either as an ordinary compound or as a species in solution."</p>