Australia's Science Forum

Hi guys, I have to make cakes of synthetic copper mineral ie copper carbonate, sand, plaster and water but the recipe doesnt give any amounts Has anyone out there done this? and if so could you give me a rough guide to ratios otherwise I can see myself spending all day trying different combinations Ive tried googling to no avail! cheers in anticipation MariaC

Oh heck, made that a long time ago. There is probably no recipe, just put some of each in the plaster of paris and add enough water to set the plaster. I used to put the wet mixture into old 50ml syringes with the top cut off, and then push the stuff out, so they looked like a core sample. They were quite obviously bluish when made.

Do a search here for copper ore and you'll probably come up with something. I usually do it in ice cube trays. I make up the plaster in a container then pour it into the ice cube tray and add I think 1-2 g of copper carbonate and stir with an applicator stick (like a giant tooth pick - a tooth pick would probably work) making sure no powder is left clinging to the sides or bottom. I don't remember using sand but that probably explains why last time I made them they were so solid the kids couldn't even smash them with hammers!! At a guess I'd say about 3/4 teaspoon of sand per ice cube but like I said, that's just a guess. Someone else can probably give you a better idea!

Oh yeah, and ask your teacher if the kids are just extracting the copper or if they are meant to be calculating the percentage. If they are calculating it then you need to be a little more accurate and probably use a higher amount so they can have decent numbers to work with.

I just do it fairly roughly - a couple of teaspoons each of Copper Carbonate, Plaster of Paris, and Sand. I make it in a takeaway tray, and then crack it into pieces. The kids have to weigh out their own piece before they begin, and that calculation becomes part of the process. Obviously, they should all get a similar final percentage yield, even if their quantities differ.

Thanks for the answers, it only had to be done "rough" for Yr 7, but wasnt sure of ratios so as it would set. All done now, will let you know how it goes on Mon! MariaC