Copper and copper (I) oxide can be determined visually, based on color.
Copper (II) oxide and copper sulfide, both of which are black, cannot be easily determined visually. Copper sulfide should be insoluble in most common liquids. On the other hand, copper (II) oxide is soluble in many acids and some bases.
Try scraping the black material from a copper test rod onto weighing paper. Then
Transfer that into a test tube. Add some dilute hydrochloric acid and shake (you might be able to get by with distilled white vinegar...Don't know). Take a look at the residue on the bottom of the test tube. I don't know how long it will take for copper (II) oxide to dissolve, but it should. If you are using white vinegar, it could take along time ( maybe weeks). Copper sulfide should stay black and not dissolve.
This is an educated guess only, based on published data. I haven't tried it. And Murphy's law seems to be as strong as many others.
That is such a good idea, @Ag8n!! We should definitely try this. @sara, what would you think about trying this with copper strips that are colocated with Purafil coupons, and we could look at the dissolution rate and extent alongside Purafil's reported oxide/sulfide ratios.
@Ag8n -- would you like one of our prototyping kits? We're almost ready to start shipping them out, and @asnow and @bronwen can get one over to you if you're interested. Thanks!
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