 All right, your identification of reaction type always starts with just the basic five, the synthesis, the decomposition, the single replacement, the double replacement and the combustion. Once you're done, you go back and check your double replacement reactions to see if they are precipitation reactions. And to do that, you need to be able to read a solubility table. A solubility table lists common ions, positive and negative, and it tells you if the combination of those ions would produce a soluble compound, something that dissolves in water, or an insoluble compound, something that does not dissolve in water. What you do is you find your ion across the top, so we're working with potassium. This would be potassium's column. And then you find your negative ion down the side. So let's say we were doing the combination of potassium and iodine, K-I, potassium iodide. Again, we would find potassium across the top. We would come down to the iodine row, and we see in here it says SOL. That means soluble. What that means is if we were dealing with this in a chemical reaction, this substance would dissolve in the water that's around. And when we abbreviate it state, we would abbreviate it as A-Q for aqueous, because it's soluble. It does dissolve. Now let's take a look at a different combination. Let's do magnesium and hydroxide, M-G-O-H2. Again, we find magnesium right there. We come down to the hydroxide row, and it says insoluble. Now what insoluble means is it won't dissolve in water, so if this were a chemical reaction, this would stay in a solid state, and so we would abbreviate it as S. We use these states to identify a double displacement or double replacement reaction as being either just a plain old double replacement or being a precipitation reaction. And in the precipitation reaction, we're looking for a very specific pattern. We want two aqueous to combine together and give us a solid. We got to have that solid being produced by the two aqueous solutions that are reacting with one another. So let's go through this reaction here and figure out if it is a precipitation reaction or not. So our first substance is the lithium sulfide, LI2S. So we go to our table here. We find lithium right there. We come down to the sulfur row, and it's got soluble written in it. So that means in our equation here, we're going to call this an A-Q. That dissolves in water. Now we're going to go to the silver nitrate. So again, we come back to this. We find the silver. Silver's right there. We go all the way down to the nitrate row, which is right here. And it says soluble in the box. So we mark this one A-Q. Now back to lithium, lithium, and nitrate this time. So again, we go back to our table. Here's lithium, come down to the nitrate, soluble A-Q, and then the silver sulfide. So again, back to the silver column over here, down to the sulfur, insoluble. That means this is an S. So we look at our pattern here, aqueous plus aqueous, producing solid and aqueous, aqueous plus aqueous, producing solid and aqueous. It doesn't matter what order those are in on the product side, as long as you have a solid there being produced by your two aqueous solutions. This is precipitation. Again, if I come up with any other pattern, like an aqueous plus a solid producing two aqueous, that's not a precipitation reaction. If it had been two solids making two aqueous, that's not a precipitation reaction, whatever. Two aqueous making a solid, that's what you need.