 Ionic equations can also help us to better understand or represent what's going on in some reactions, such as single and double displacement reactions. Let's take an example. Imagine copper reacting with silver nitrate to give copper nitrate and silver metal. Now, the first thing is to write the ordinary chemical equation, like this, with subscripts showing the states. Copper nitrate is soluble, so when it's produced it dissolves straight into aqueous solution. Alright, now let's think about it in terms of aqueous ions. Which of these compounds or elements physically exists as separate aqueous ions? Well, it's the ones that are marked with the aqueous subscript and which are ionic. The others are solid. So let's rewrite the equation showing those compounds as separate ions. There are two silver nitrates, so that gives us two separate silver 1 plus ions and two separate nitrate ions. On the other side, the aqueous copper nitrate will become one copper 2 plus ion and two nitrate ions. The metals, copper and silver, are not ions. They are metal elements made of neutral atoms, shiny and malleable and with other metallic properties. They are also solids and not dissolved. Okay, what we have now is called a full ionic equation. All the ionic aqueous species are shown as separate ions, and everything else is shown as normal. Can you see anything that doesn't change during this process? That is something that is the same on the left and the right of the equation. Well, it's the two nitrate ions. They're there at the beginning and they're still there unchanged at the end. This means that although they're present, they aren't actually changed by this reaction. We call this type of ion a spectator ion. It's there, present, watching, if you like, but it doesn't actually take part in the reaction. The other species do take part. The copper goes from neutral copper atoms, the metal, to copper ions, and the silver ions from the silver nitrate turn into neutral silver metal. So in order to get to the bottom of this reaction, we can cross out the nitrates since they aren't changed, and we just show the essence of what's going on. And what we have now is called a net ionic equation. Visually, if you were doing that reaction, this is what you'd see. The aqueous silver nitrate is a colorless solution, and here you can see the reddish copper wire sitting in it. Now copper 2 plus ions, which are one of the products, have a blue color. So as the reaction proceeds and the copper metal gets turned into copper nitrate, the solution becomes blue. Simultaneously, the silver ions in solution that you started off with are precipitating out as silver metal. So the copper wire gets covered in a fur of metallic silver. OK, here's one for you to try. This is a double displacement reaction. A solution of lead 2 nitrate is poured into a solution of potassium iodide, resulting in aqueous potassium nitrate and a yellow precipitate, that's a solid, of lead 2 iodide. First, write out the full ordinary balanced equation with complete formulae and subscripts. Then rewrite it to show the aqueous ionic compounds as separate ions. That'll be your full ionic equation. And finally, cross out any spectator ions to give the final net ionic equation.