Half equation question

[dekoyl]

Thanks again Wizard and Coblin =]

However, are you sure the question didn't ask for an "ionic equation"?

Yep :O "Balance the following redox reactions by first writing the reduction and oxidation half equations.[/size]

[NE2000]

From my understanding, I think that reaction can occur, and I've seen it come up a few times where something will simply have no ionic equation. Like in the above case, this seems to happen when everything's aqueous, and you basically just have a displacement of ions occurring. I'm not too great at chem overall, so I'm actually quite lost as to how both sides of that equation differ if they can equally be written as the sum of the individual ions anyway. I'm pretty sure it's something to do with the bonding between the particles, but yeh I'm not too sure about the net effect.

Just a guess. Perhaps the difference is in regards to the reassociation of ions. Eg. if you were to cool this solution down to decrease the solubility of the sodium sulfate then you will find sodium sulfate crystals forming rather than sodium chloride. Or alternatively, perhaps if you evaporated the water the crystals post-reaction would be sodium sulfate.

Anyways, it doesn't seem to be particularly important...

[Collin Li]

Oh, yeh that's what I was trying to say. The basis of this is that and are totally different. That's what I meant by a change. What isn't change is when say i.e. react to become other ions (e.g. and or something), but in their new aqueous form, still technically remain as

OK all good then

But the reaction you picked was interesting. If you had a reaction:


Then what of the ionic equation? Would such a reaction even occur (or would the acid rather react with water or something)? Do the spectator ions actually react at all or are they just there 'spectating' as the reaction occurs, because in the above case (if a reaction were to ever occur like that) then the solution before and after the reaction would not be different at all I would guess. I once got this type of equation in a test this semester and I got marked right for saying 'all are spectator ions' but it still bugs me.

Hm... didn't notice this discussion beforehand.

Sulfuric acid and hydrochloric acid are covalent molecules. It's not a mere rearrangement of ions, because you cannot think of these species as ionic compounds. Hence, the ionic equation exists (you would include sulfuric acid and hydrochloric acid in whole) - sodium ions would disappear.

[NE2000]

Oh...

So if you had:


Then would be ionic equation be:


or would it be


?

I'm just confused coz I learn't this year that with acids you would just have the H+ in the ionic equation

[Collin Li]

Yeah, the first one is right. Don't worry too much about why you only have sometimes, but it's got to do with the fact that strong acids will do this to nearly 100% completion:



This means that you can think of the acid as two ionic species, because the covalent molecule isn't even there anymore.

Reactions that ignore the conjugate base, do this because they just want to show the interaction of the acidic proton with the other species.

But in a general chemical equation, we want to show this change in chemical state (from covalent to ions), so we technically should include the chlorine atom as part of the hydrochloric acid molecule on the left-hand side (because it was originally that). So we do include this in the ionic equation.