AP solution, brown precipitate?

[HowlingMad]

Hello all,
I was using my AP solution for the third time, stuck some gold plated fingers in it and now have a brown precipitate in the bottom and it is a fairly significant volume. The AP used has only been used with fingers. What am I looking at?

I took a small sample after filtering it out. Added Hcl and it immediately went into suspension again.

Added a couple of drops of Nitric and received a very small amount of white precipitate. The white precipitate was about 1/20th of the sample size. Sulphuric Acid or water put this back into suspension.

Should I use the reactivity chart to determine what it is? I have pure samples of lead, tin, copper, nickel, and aluminum. Also some steel laying around.

Thanks in advance.

 

[FrugalRefiner]

Let's slow down and make sure we agree on terminology.

I was using my AP solution for the third time, stuck some gold plated fingers in it and now have a brown precipitate in the bottom and it is a fairly significant volume. The AP used has only been used with fingers. What am I looking at?

I took a small sample after filtering it out. Added Hcl and it immediately went into suspension again.

What do you mean by "went into suspension"? Do you mean it dissolved? That would mean it went into solution.

Added a couple of drops of Nitric and received a very small amount of white precipitate. The white precipitate was about 1/20th of the sample size. Sulphuric Acid or water put this back into suspension.

You added a couple of drops of nitric acid to some of the brown precipitate and got a white precipitate? And then you added sulfuric acid? To what? The brown precipitate, the white precipitate? And it went back into suspension or solution?

Should I use the reactivity chart to determine what it is? I have pure samples of lead, tin, copper, nickel, and aluminum. Also some steel laying around.

The reactivity series is useful when you're cementing metals. One metal goes into solution and replaces another metal that's already in the solution. But you're dealing with salts of metals, and what precipitates is controlled by solubility of those salts, not the reactivity of the various metals in solution.

Dave

 

[HowlingMad]

Dave,
Thanks for replying, and I'll try and get the terminology right.
Yes, the brown sludge went back into solution once the Hcl was added.

You added a couple of drops of nitric acid to some of the brown precipitate and got a white precipitate? And then you added sulfuric acid? To what? The brown precipitate, the white precipitate? And it went back into suspension or solution?

The Sulfuric was added to the existing sample and the white precipitate went into solution.

The reactivity series is useful when you're cementing metals. One metal goes into solution and replaces another metal that's already in the solution. But you're dealing with salts of metals, and what precipitates is controlled by solubility of those salts, not the reactivity of the various metals in solution.

Right, got it now. Never have really dealt with any salts so...

 

[HowlingMad]

Dave,
I created another sample without a lot of screwing around.

The picture below is 7ml Hcl, with 15 drops of Nitric added. I have not added any Sulfuric at this point. I tested with Stannous just for laughs and it came up negative.

 

[glorycloud]

The brown "sluge" in the filter looks like copper to me.
When I reuse my AP a lot, that seems to happen. When
I add some HCL like you did, the copper goes back into solution.