What is this yellow precipitant

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Bluebloomer

Well-known member
Joined
Jul 7, 2014
Messages
140
Location
Netherlands
I was cleaning the copper pipes, I used in cementing processess. All the copper had a white / grey coating, so I used some clean water and a scuffing pad to clean the copper and take the white / grey coating off.

After the copper was cleaned, I put it in a fresh bucket of water, and the copper turned bright red right away. Okay, whatever.. ? Then I poured the water from cleaning the copper in a big glass jar, and the white / grey coating turned bright yellow after settling.

Could this be iron oxide from some iron that was stored with the copper in an alkaline solution, or could it be some other metal, like the white / grey coating ?

I was asuming the coating on the copper was tin.
 
Does it dissolve in hydrochloric acid? If so, what is the color of the solution immediately after dissolving and then later on after standing for a couple of hours?

Göran
 
The liquid was a nice yellow color, I acidified it, and the yellow precipitant turned into a grey/white cloud on the bottom, it is still setteling. PH is now around 5, might have to bring it down lower. Solution is now a funny green / yellow color.
 
Greenish yellow could be some copper or iron chlorides staining the precipitate.

I was expecting the precipitate to dissolve as I suspected copper(I) chloride. Apparently I was wrong.

Göran
 
What exactly had you been cementing?
Knowing this will hopefully get you the answer your after.
 
I agree. A white/gray coating includes a lot of different things. Pictures help in identifying stuff like this.
 
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