# Color change of aqueous ferric salt when reacted with phosphate

I have a question about an equilibrium system:

$$\ce{Fe^3+ (aq) + SCN-(aq) <=> [Fe(SCN)]^2+ (aq)}\\ \text{(yellow)} \quad \text{(colorless)}\quad \qquad\text{(red)}\qquad\quad$$

The question is about what happens to $$\ce{Fe^3+}$$ when you add $$\ce{HPO4^2-}$$ to the solution above.

I'm not sure (that's why I'm asking), but when you add $$\ce{HPO4^2-}$$ to the solution it reacts with $$\ce{Fe^{3+} (aq)}$$ and forms $$\ce{Fe2(HPO4)3}$$ (I’m guessing):

$$\ce{2Fe^3+ (aq) + 3HPO4^2-(aq) -> Fe2(HPO4)3}\\ \ \ \ \ \text{(yellow)} \quad \text{(colorless)}\qquad \qquad\text{(colorless)}\qquad$$

My hypothesis is: When you add $$\ce{HPO4^2-}$$, there is a "loss" of $$\ce{Fe^3+}$$ because $$\ce{HPO4^2-}$$ reacts with $$\ce{Fe^3+}$$. This also means that there is a chemical shift to the left (The solution produces more $$\ce{Fe^3+}$$), and because $$\ce{Fe2(HPO4)3}$$ is colorless the solution also turns colorless.

• Please COMMENT if you also want me to elaborate on something. – Hilmar Oct 8 '18 at 16:45
• Well, that's still reposting, from new account this time. You know you can edit your posts to improve them? And improved old, post may get reopened. Check out how A.K, improved equations, earlier they looked as bad in old posts. chemistry.stackexchange.com/questions/102629/… – Mithoron Oct 8 '18 at 19:47
• And what do you mean by saying that my equations look bad? They are just fine? – Hilmar Oct 8 '18 at 20:18
• Well, compare before and after edited with mathjax – Mithoron Oct 8 '18 at 21:00
• My first point was that one question shouldn't be asked multiple times. So in the future, if question gets on hold, don't ask it again, but edit it. This post looks mostly OK, though isn't perfectly clear. You ask what's the reaction or why product is colorless, while substrate isn't? – Mithoron Oct 8 '18 at 21:38