 The other kind of displacement is a double displacement. In this reaction, two ionic compounds, usually both dissolved in water, but not necessarily. Swap ions to produce two new compounds. If one of these new compounds is insoluble in water, it'll precipitate out as a solid. An example of this reaction is the reaction of sulfate salts with barium nitrate. Barium nitrate is soluble in water, but barium sulfate is not. It's a white powder. So if barium nitrate is mixed with any other sulfate salt, then the barium and the sulfate get together and form a white precipitate. And this can be used as a test for sulfates. The reaction that I've written out here is of sodium sulfate with the barium nitrate. The photo shows the reaction happening in a test tube. The sodium sulfate and the barium nitrate are both dissolved in water, and because they're colorless, the solutions look exactly like water. However, when one is added to the other, the ion swap and barium sulfate forms as an insoluble white precipitate. Sodium nitrate is the other product. When it's in its pure solid form, it's also a white powder. But because it is soluble in water, you don't actually see it form here. Here's a quick task for you. Using what you know about separations, the way that you could recover the two products of this reaction, barium sulfate and sodium nitrate, in their pure solid form.