My 1/2 Q thread

[WhoTookMyUsername]

XD


How can i tell what state compounds are naturally found in?
Are there any rules to help?
My teacher said all acids are (aq) but acetic acid etc. isn't?

thanks (yes i am noob at chem, been focusing on the bio )

[Tashi]

Well you can use your solubility table. Don't worry too much, once you use them over and over again you become familiar with all the different compounds so you just need to practice.

[REBORN]

Pretty sure acetate acid is aq

[pi]

Pretty sure acetate acid is aq

It's acetic acid.

And in fact you are both correct, and incorrect. It can be either a liquid (normally called glacial acetic acid, i think) or diluted as an aqueous solution

[WhoTookMyUsername]

Thanks for the help:)


How can you determine the extent to which an acid / base dissociates in water? ( strength of acid ) without specific figures ( e.g. When it says, list following according to electrical conductivity)?


2) why is nano3 neutral when na3po4 is not?

I know na 3 po4 dissociates, then po4 accepts hydrogen atoms like bases do, but why is it not the same with nano3?



3) in the acid base reacitn between ammonia and hydrogen chloride, do you leave ammonium and chloride ions separate or do they become ammonium choride and why?

Tanks

[Mao]

1) The best way is to use acidic constants, but that's unit 4 knowledge. As far as 1/2 goes, you have a rule of thumb, which is:
Strong acids = complete dissociation = HCl, H2SO4, HNO3
Moderately strong polyprotic acid = H3PO4
Weak acids = CH3COOH, almost everything else

2) The conjugate of NO3- is HNO3, a strong acid. When a strong acid reacts, it is because it is extremely favourable for it to dissociate, like going downhill with a sharp slope. For it to go backwards, you need to go against the original reaction (i.e. going uphills with a sharp slope), which is very hard. Therefore it doesn't happen (or only does so at a negligible rate). This is why NaNO3 is neutral.

3) In solution, they are dissolved ions, and thus are separated from each other. Though for simplicity, you could write , the (aq) implies they are dissolved/separate. is a more explicit, but nonetheless equivalent, way of saying the same thing.

[WhoTookMyUsername]

Thanks Mao Nice answers helped clear it up really well

just as an extension on question (2)
is another way of looking at it to say Nitrate (compounds of) is highly soluble but phosphate not?
So HNO3 would dissociate removing its 'basic' effect, whereas H3PO4 would not?
Does this apply for all the ions in the solubility chart

?

Thanks

[Mao]

just as an extension on question (2)
is another way of looking at it to say Nitrate (compounds of) is highly soluble but phosphate not?

(this response is mostly speculations, and most of it will be above the VCE level, but here it is anyways)

I don't think acidity can be solely explained with solubility. I am not sure what the relative solubilities of HNO3 and NO3- are, and so I cannot make a good judgement of if solubility play a role in deprotonation (acid donating a proton). I do know that this process can be highly exothermic, and the chemical energy released far outweighs any free energy change from dissolution, so it is unlikely solubility plays an important role. This does not mean it can be completely neglected though, it is plausible that for some molecules this contribution is relatively important. Another point to consider is that water has a harder time dissolving ions with higher charge density, so a multiply-charged ion such as the phosphate ion would have a strong ionizing effect on neighbouring water molecules, essentially ripping H+ from nearby waters due to its large negative charge.

The science of dissolution is not well understood yet. For now, probably best to treat ionization of acids/bases and dissolution separately. Maybe one day a theory will be developed to relate solubility with other phenomena in water chemistry.

[WhoTookMyUsername]

okay thanks mao -
yeah in this case compounds of No3 are highly soluble, whereas compounds of Phosphate are not (excluding a few, but INcluding H3PO4)

[Mao]

okay thanks mao -
yeah in this case compounds of No3 are highly soluble, whereas compounds of Phosphate are not (excluding a few, but INcluding H3PO4)

In my opinion, solubility is not a good way to look at relative basicity.