Learn about Junior Chemistry, Solutions 7, in this comprehensive video by bannanaiscool.
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If dissociation equations are true, and they are you'll have to trust us on that one, then all those equations that we were doing before in the balancing of chemical equations section they're not necessarily all right. Because if they have compounds that are aq in them, aq’s is ionic compounds they don’t actually exist they dissociate into their ions. So we can’t write non-ionic equations like this and think that they're accurate, although they do work kind of well for most intents and purposes. So look we've got Zn and HCl and we need two of them in the balanced equation to react to produce ZnCl and hydrogen gas. So let’s say that’s the equation, that’s the non-ionic equation how do we get a net ionic equation out of that, what’s really happening? Is this happening? No not really. So we need to take anything that’s aq and break it down into ions but only aq’s. Don’t breakdown the solids, don’t breakdown the gasses only breakdown the aq’s ones like this. So here is a total ionic equation which is anything that’s aqueous broken down into ions—look, we’ve got the zinc solid and we’ve got two HCl which can actually dissociate into H positive and Cl negative. And since we have two of those we have two of these and two of these—two H positive and two Cl negatives. That’s really what constitutes all the reactants here. Now the products are well there is the ZnCl compound which you can break down into ions. Zinc ions – Zn two positive aq and then two Cl negative aq, and then the hydrogen gas we leave it alone because it’s a gas. This is the total ionic equation. Now take a look, from one side to another certain things change, but certain things remain the same. The Zn becomes an ion, the H positive ion becomes gas, but Cl stays the same. So really in that reaction Cl doesn’t do anything but just watch. It’s called spectator species. Chemicals can be species. And so we take the spectators out nicely balanced two and two and then we get our net ionic equation. How do we do that? Well you probably have to write it again I just have to use my eraser and look at that. Zinc solid and two hydrogen ions makes zinc ion plus hydrogen gas. It’s all balanced and look at the charges, two positive and zero here makes two positive total in the reactant side. Two positive and zero there makes a total of two positive on the product side. So not only are we balance with atoms but we’re balance with charge. That’s important later on Chemistry II.