Chemistry Precipitate Help?

Question

Ok, well the other day in chemistry we were doing precipitation reactions, and now that i'm going through the theory I'm really confused. Our teacher told us that not all of the reactions should have formed precipitates but all of them did, well at least i think they did. The teacher also said that a precipitate was a solid that falls to the bottom, so i wasn't sure if all of them actually formed precipitates.

When i combined barium chloride and sodium carbonate, the solution turned white but no solids were formed, is this counted as a precipitate? The theory says that a precipitate should have formed.

And with copper(ii) sulfate and sodium carbonate the substance formed settled on the bottom and floated on the top, is this called a precipitate? The theory says that copper carbonate should have formed.

If you have any idea about all of this it would be really helpful!! thanks.

Alan F · Accepted Answer

A precipitate is simply something which is not soluble in the solvent present. It doesn't have to float or sink, but should be visible.
In the first case the barium carbonate has precipitated as fine particles. These appear as a white opaque solution. As the particles were very fine they would be slow to settle. If you just left the mixture the barium carbonate would eventually settle out, leaving a clear solution.

Copper carbonate, does form as a precipitate. It should in theory settle out to the bottom, which most of it did. However some fine particles get attached to fine air bubbles when you were stirring the mixture some air bubbles were formed. 

Hope that helps

Anonymous · Answer

Simply, if the solution tuend white, then a white persipitat was suspended in solution. Just needs time (somtimes alot of) to settle. sodium chloride was precipitated aswell as i presume the barium carbonate both of which are white.

Again yes, copper carbonate was formed along with sodium sulphate, copper carbonate being green and sodium sulphate being white, (ALLTHOUGH BECAUSE OF COMPLEX BONDING WITHIN THE WATER MOLECULES COLOURS MAY BE SLIGHTLY DIFFERENT FOR EXAMPLE HYDRATED COPPER SULPHATE IS A DEEP BLUE, WHEREAS COPPER SULPHATE UNHYDRATE IS LIGHT BLUE)

tl;dr? Both wore percipitates =]

Chemistry Precipitate Help?

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