Quick question, since FePO4 is insoluble, will that mean a precipitate will form? During the experiment I don't remember seeing a precipitate. Is that my error, or is the precipitate hard to see?
Sure. Adding Na3PO4 will make a big difference. FePO4 is almost completey insoluble in water; therefore, adding Na3PO4 will form FePO4, that will decrease the concentration of Fe^+3 (ferric ion) and that will make the equilibrium shift to the left.
Another chem question. For the equilibrium system Fe+3 + SCN- <--> FeSCN+2, from adding Fe(NO3)3 to KSCN, what would happen if you add KCl. Which way would the system move?
This is a question on Le Chatlier's Principle and the common ion effect by the way.
I don't think the equilibrium would shift either direction. KCl contains no Fe^+3 or SCN^- or FeSCN^+2. And KCl will not react with either Fe(NO3)3 or KSCN. The only thing KCl can do is to increase the ionic strength of the system and that may affect the activities that go in the equilibrium constant expression. But I doubt the person asking the question has that in mind.
FePO4 is insoluble and you should see a ppt IF the concentration of ferric ion is high enough. But you must remember that the Fe^+3 + SCN^- ==> FeSCN^+2 is such a sensitive reaction that it takes just a smidgen of Fe^+3 to form the complex ion. So you might not SEE a ppt if you weren't looking for it.
I wrote my answer after you posted about LeChatlier's Principle and common ion effect. There is no common ion (except K of course) but KSCN is soluble as is KCl. I still don't think the equilibrium will shift. Check my thinking.
One thing for sure. If KCl or Na3PO4 is supposed to shift the reaction and we know KCl won't do it, then Na3PO4 must. From an experimental standpoint, however, we know Na3PO4 should shift the equilibrium.
Thanks alot, you've been a great help once again.
Would it shift it enough left to make it lighter (light yellow/orange) but not form a percipitate? Fe^+3 + SCN^- ==> FeSCN^+2 is "colorless --> deep orange."
Yes, I intended to ask if the color changed. That would be a visible indication that the equilibrium had shifted.
And hopefully the last quesion, when I added the KCl it also turned lighter. Now you could argue not as when light as when I added Na3PO4. Would I be correct to assume that it was just diluted because we added 20 drops to maybe 2,3 drops max (we divided 10-12 drops into 5 beakers equally)?
Then, does Na3PO4 move left just slightly?
If you added KCl and Na3PO4 as solutions, then yes the diminuation of color could be due to the dilution. There is no way to say how much Na3PO4 will shift the equilibrium. I don't have the equilibrium constant, we haven't talked about concentrations of Fe(III) and SCN^-, or Na3PO4 or how much Na3PO4 was added. We can only say the addition of Na3PO4 should shift the equilibrium to the left. There is also the possibility that Fe(III) and PO4-3 form a complex ion but I haven't been able to verify that. That would help explain why you saw no ppt of FePO4 and it would decrease the Fe(III) concentration the same as a pptn of FePO4 would decrease Fe(III). Unless you can verify that Fe(III) and phosphate form a complex ion, however, I would stay with the FePO4 ppt explanation. I found a site on the web that lists Ksp for FePO4 as 1.3 x 10^-22 which means the molar solubility of Fe(III) is 1.1 x 10^-11 which is, inded, a small number.
I know no one will look at this for a while, but when you add KCl to the equilibrium Fe+3 + SCN- <--> FeSCN+2 it shifts right and becomes a lighter red since the complex ion FeCl4- forms. There is no dilution involved. This is a little late for you Karl, but hopefully someone else can use this information.
Lia, won't the equilibrium reaction shift to the left, since the system will try to minimize the disturbance by creating more Fe(3+) ions? Therefore, the complex ion FeSCN(2+) will have to break up into Fe(3+) and SCN(-) in order to reestablish equilibrium.