Chemistry Equilibrium Lab

Question

Hi!

I did a lab where I affect the equilibrium of the following: Fe3+ (aq) + SCN- (aq) <-> FeSCN2+ (aq)

Fe3+ gives a yellow/orange color, SCN- is transparent and FeSCN2+ is red.

A mixture of Fe3+ and SCN- was therefore distributed evenly in two test tubes, so that I get the equilibrium above and can change it. The color by then was sorta dark orange

What I did first was add silver nitrate in on of the test tubes. The silver reacts with the SCN- so that a salt AgSCN is created. What I see then is that the mixture in my test tube is light yellow and I see a white cloud on the bottom, which I presume is the AgSCN salt.

In the next test tube I added hydrogen phosphate, HPO4(2-). The whole test tube became transparent. I do not understand why it became transparent. Why is it not like above and a white cloud of salt appears? When I put hydrogen phosphate I should get a salt of it with iron?

Thanks in advance!

Answer 1

You are correct about forming AgSCN in your first test tube and this is a white precipitate.

In your second test tube, you will not form FeHPO4 but rather you would form FePO4, iron (III) phosphate. This is a soluble compound and thus you would not see a precipitate form.