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Net Ionic Equation - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

A net ionic equation is an equation for a double replacement reaction which shows only the reacting ions and omits the spectator ions.

Alright so we're going to talk about net ionic equations which actually an extension of double replacement reaction. So let's go into detail what exactly is happening when you have double replacement reaction. Okay so double replacement reaction is when 2 ionic compounds come together and switch partners right. So typically we do have is, it's an aqueous solution, meaning that these compounds are in water and making solutions. So let's take for example we have sodium hydroxide when you put it in water it actually breaks up into its ions. We have a sodium ion and a hydroxide ion, the same thing happens with all ionic compounds so let's reiterate that with copper 2 chloride put that in a solution or in water to make a solution and we have 1 copper ion, 1 copper plus 2 and 2 chloride ions in the beaker.

Okay great but what does that mean now? Alright so let's say we put the, add it to these 2 beakers together to see what would happen. Well most of the time, you're going to have a precipitate and a precipitate is solid form or solid pieces within in that solution. Since - solid will actually happen. You probably have solubility chart that your teacher might have given you, that tells you what actually makes a precipitate. Simpler way of writing precipitate instead of having to write the whole word is PPT so you might see that actually in the future too. So this actually means precipitate, these words are pretty important also, within this reaction this is going to still be aqueous and this is going to be our actual precipitate. This is going to be our solid, that's actually going to be formed. So we're going to say NaCl the product is soluble meaning it is dissolvable in the solution, it will break up into its ions it'll still be in solution.

This is going to be insoluble meaning that it's going to be the precipitate meaning it's going to be the solid of this reaction. This is actually going to stay together. So let's write this out more accurately to describe exactly what is happening. So we look at the complete ionic reaction, we're going to break this up, we don't like it together because we know that they separate in solution as we've mentioned earlier so instead of writing NaOH I'm going to write Na+NOH- okay then I'm going to break this up into it's ions also because it's broken up it's an aqueous solution. So we're going to say Cu plus 2, plus chloride ions, this 2 comes out. We have 2 of these guys, 2 chloride ions, it's going to produce salt which we said is soluble it's in an aqueous solution.

It's going to be broken up to its ions Na plus, plus Cl minus and this is a solid so it stays together. We're going to say CuOH2 now actually I actually forgot to balance the original equation. We're going to have to go back and make sure this is balanced, so we can do it properly. Okay so there's, let's go back up here, there's 2 chlorines, there needs to be 2 chlorines here which means I have 2 sodium, 2 sodium there, 2 hydroxides, 2 hydroxides this is balanced. This will also change our complete ionic equation let's put a 2 here, we have 2 of these guys both of them, this 2 will tell me I have 2 of these and 2 of these. Okay so it's balanced this is helpful. Okay so now we have this long equation, this is actually much more accurate description of what is actually happening in the reaction.

Let me go into something called spectator ions. When you think of the word spectator you might think of like a basketball game, when you watch a basketball game you're a spectator of that basketball game right. If you go to like a wizards game you would be a spectator at that wizards game. You wouldn't actually be involved in that with this game, you're not affecting the outcome of that with this game, you're actually just there watching the event happen. That these spectator ions is the exact same way, okay they're just watching the reaction take place, there're just spectators. They don't really do anything, they don't affect the outcome of the actual reaction. So what do I mean by that, what's a spectator ion? Okay well there're ions on both sides of the reaction, they haven't changed. So for example we have a sodium ion here, and a sodium ion here, that's a spectator we can actually cross that guy out he is not doing anything in this reaction.

Then we have hydroxide ion we don't have one over here so we can't that's not a spectator. We have copper over here, we don't have copper over here so that's not a spectator, we have 2 chloride ions and yet we have 2 chloride ions here that guy is the same on both sides, he is a spectator he's just watching the event happen, he is not important. So then we have our leftovers and this is how we get to our net ionic equation, our net ionic reaction. So I'm just going to bring those down and I'm going to say 2OH minus plus Cu plus 2 gives me CuOH2 and I'm going to make sure this is our solid. This is our net ionic reaction, this is what actually is happening within this reaction. So let's take this and go up and do this one more time just to make sure that we understand.

Okay an aqueous solution of aluminum chloride and sodium hydroxide react to form solid aluminum hydroxide. Alright let's break this up into its overall reaction. So aluminum chloride we know this is Al+3 and Cl and this is a minus so, when they actually make their compound it's going to be AlCl3 and we know it's an aqueous solution so we're going to write aq okay reacts with sodium hydroxide, we have sodium which we know it's Na this is plus, hydroxide OH it's a minus so together they're just going to be NaOH and this is an aqueous solution also reactive from a solid and this tells us what precipitate is aluminum hydroxide. So we know aluminum hydroxide is going to come together, this is Al+3 OH and a minus, so it's going to be AlOH3 and then we have another product so we did the outsides ones, we're going to do the inside ones Na and Cl as left over so you can just say NaCl and this is our aqueous, this is our soluble.

Okay so let's balance this equation make sure it's balanced correctly, we have 1 aluminum, 1 aluminum, 3 chlorines, let's make 3 chlorines here that makes 3 sodium, so let's do 3 sodium on this side making it 3 hydroxides, 3 hydroxides good great it's balanced. Alright so let's do a complete ionic reaction we have to break it down don't forget aqueous solution will be broken down into its ions. Let's do that, we have Al plus 3, plus 3Cl minus ions plus 3Na plus ions plus 3OH minus ions yields this is our solid, we're going to keep this together AlOH3 and then this is aqueous so we're going to break that up. Okay so now we have to find our spectators again, so which ones are our spectators? Meaning they're the same on both sides, well I have 3 Na's over here and 3Na's over here I cross those out. 3 chlorides here, 3 chlorides here I cross those guys out.

Now our left over this is our net ionic equation, we're done Al plus 3, plus 3 OH minus yields AlOH3 this is our solid for precipitate. It's completely balanced so we're looking good awesome. One type of double replacement reaction that you might see or that you can put into non-ionic equation is what we call a neutralization reaction. This is also double replacement reaction. The reason we call it neutralization because we have a hydro bromic acid then we have sodium hydroxide which is our base. So together an acid and a base is going to be neutral meaning it has a PH of 7. So this is what we call a neutralization reaction. So let's do that when they trade places or actually have the reaction occur the H is going to be now the OH so HOH is another way, a funny way of writing water so I'm just going to write water they had me say HOH is water.

And then we have sodium and bromide come together okay so whenever we have water this is actually a liquid. Water is not aqueous water is with aqueous it's a liquid solution. Okay so not a solution it's just a liquid, it's in liquid state, so this guy, anything that's not aqueous, is going to stay together, only thing that breaks apart is aqueous it is gas, that stays together, if in liquid stays together okay so water is going to stay together, this actually is aqueous, it's going to break up so let's do it. H+, plus Br- did we make, make sure it's balanced? Yeah it's balanced Br-, plus Na+, plus OH- yields H2O we're keeping it together because it's a liquid and NaBr, Na+ and Br- we break up, we cross out our spectators Br is a spectator Na is a spectator. So we're left with H+ OH- yields H2O as our final reaction. And this is common also this can totally be an equation and be just fine don't forget to include that's liquid. And now that's pretty much how you do an ionic equation.