net ionic equation (thing)

In the interests of node your homework, I've decided to enlighten everything2 on this obscure bit of high-school chemistry class nonsense. I learned this in the context of acid-base reactions (neutralization, titration, etc.), so that's how I'll explain it.

Acids and bases are never wholly concentrated- they must be placed in water for the chemicals to ionize (split up into their respective ionic parts). For example:

H₂SO₄ (sulfuric acid) ionizes in several stages. First, one H⁺ ion will separate to yield this:

This is called the first ionization potential. Actually, the equation isn't quite correct since H₂O should be over the arrow to show that that's the catalyst for the ionization, but hey- you try doing that in html. After this, another H⁺ will part company in the same way:

This is the second ionization potential. Now the acid is broken all the way down into a sulfate ion and a hydrogen ion. In an ionic equation of any kind, this process is already assumed to have occurred, so the chemicals are already broken down into their ionic forms, like so:

Again, there's really supposed to be a little H₂O over the arrow. All those little things that look like this _(aq) or this _(s) signify the state of the chemical, which is important for finding out whether they ionize in water or not. _(s) means the chemical is in solid state and _(aq) means that it's in an aqueous state. When all these ionic parts react, we get a double replacement reaction that looks like this:

This is a nice little ionic equation. As you can see, Ba⁺² _(aq) and SO₄^-2_(aq), both soluble in water, react to form to form BaSO_{4 (s)}, which is insoluble in water. To find out how a compound acts in solution (whether it's water, acid, or anything else) you have to look at a solubility chart, which can usually be found in the index of any chemistry textbook or on the internet.

In contrast to a run-of-the-mill ionic equation, the net ionic equation lists only those chemicals that actively participate in a chemical reaction. The chemicals you don't include in a net ionic equation are those that don't change during the reaction, for example:

The parts of the equation in bold are the ones you would not include in a net ionic equation, resulting in:

This equation means that one sulfate ion and one barium ion in a solution would combine to result in solid barium sulfate, probably as a precipitate (solid stuff at the bottom of the liquid, like dirt seperating from water).

There you are- one more simple thing unnecessarily complicated.