Little_Ghost_again
National Hazard
Posts: 985
Registered: 16-9-2014
Member Is Offline
Mood: Baffled
|
|
Normality and molarity
Hi
While reading a procedure I came across something thats got me wondering.
It spoke of a synth with Nitric acid and described a 1M 1N solution of nitric acid.
I thought a 1N solution of Nitric acid would be 0.5 Mols as it has 2H+ or does it?
Ifa solution is described as 1N then surely you would need 0.5M of 70% solution.
BTW the conc was given as 70% Nitric Acid
Anyone throw some light on this, I dont have a link as it was a stumble page and I only thought about it after
Dont ask me, I only know enough to be dangerous
|
|
|
Chemosynthesis
International Hazard
Posts: 1071
Registered: 26-9-2013
Member Is Offline
Mood: No Mood
|
|
Monoprotic.
HNO3.
|
|
|
Little_Ghost_again
National Hazard
Posts: 985
Registered: 16-9-2014
Member Is Offline
Mood: Baffled
|
|
I messed up I meant H2SO4, but was doing something this morning with Nitric acid, so replace all reference to Nitric with sulphuric! sorry about that
Dont ask me, I only know enough to be dangerous
|
|
|
Chemosynthesis
International Hazard
Posts: 1071
Registered: 26-9-2013
Member Is Offline
Mood: No Mood
|
|
Generally speaking, 1M would then by 2N, yes... but that is only when assuming titration of hydroxide or similar. I suppose it may be able to refer to
1M sulfuric acid as 1N if only the first protonation were of a low enough pKa to dissociate under specific conditions, but I haven't seen this.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
The concept of normality ('equivalents per litre') is also used in redox titrations. For instance 1 mol of dichromate reduced to 1 mol of Cr(III) in
acid conditions absorbs 6 mol electrons. A 1 M solution would thus be 6 N. In reality you would normally titrate with a 0.1 N solution or 0.1/6 M. Or
a 0.05 N, i.e. 0.05/6 M solution.
They don't seem to teach normality all that much nowadays, which is a shame because in many reactive situations it is easier than molarity: 1
equivalent of whatever always reacts with 1 equivalent of whatever else.
[Edited on 17-11-2014 by blogfast25]
|
|
|
Little_Ghost_again
National Hazard
Posts: 985
Registered: 16-9-2014
Member Is Offline
Mood: Baffled
|
|
Hi
actually yes I didnt mention the context!! Sorry having one of those days! It was to do with titration which is why I was confused.
Thanks again
LG
Dont ask me, I only know enough to be dangerous
|
|
|
Brain&Force
Hazard to Lanthanides
Posts: 1302
Registered: 13-11-2013
Location: UW-Madison
Member Is Offline
Mood: Incommensurately modulated
|
|
Quote: Originally posted by blogfast25  | The concept of normality ('equivalents per litre') is also used in redox titrations. For instance 1 mol of dichromate reduced to 1 mol of Cr(III) in
acid conditions absorbs 6 mol electrons. A 1 M solution would thus be 6 N. In reality you would normally titrate with a 0.1 N solution or 0.1/6 M. Or
a 0.05 N, i.e. 0.05/6 M solution.
They don't seem to teach normality all that much nowadays, which is a shame because in many reactive situations it is easier than molarity: 1
equivalent of whatever always reacts with 1 equivalent of whatever else.
[Edited on 17-11-2014 by blogfast25] |
I am so glad I read this thread for this very reason...
At the end of the day, simulating atoms doesn't beat working with the real things...
|
|
|
DraconicAcid
International Hazard
Posts: 4334
Registered: 1-2-2013
Location: The tiniest college campus ever....
Member Is Offline
Mood: Semi-victorious.
|
|
Meh. I see "normality" as an extra layer of confusion added for the benefit of people who don't understand stoichiometry.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
No, no: you can't work normalities if you don't understand stoichiometry but in that case you can't do it with molarities either!
Where I see it as useful for instance is where a 'chain' of redox reactions is used for titration: e.g. oxidise ethanol with excess dichromate,
oxidise iodide to iodine with left over dichromate, titrate iodine with thiosulphate.
Determine valences for each species (half reactions) and prepare equinormal solutions of all, e.g. 0.1 N for all solutions. Now you know 1 ml of one
always corresponds to 1 ml of the others.
I know some find it confusing but they remind me of those Brits who still can't convert pounds to kilogram!
|
|
|
Little_Ghost_again
National Hazard
Posts: 985
Registered: 16-9-2014
Member Is Offline
Mood: Baffled
|
|
| Quote: Originally posted by blogfast25 |
No, no: you can't work normalities if you don't understand stoichiometry but in that case you can't do it with molarities either!
Where I see it as useful for instance is where a 'chain' of redox reactions is used for titration: e.g. oxidise ethanol with excess dichromate,
oxidise iodide to iodine with left over dichromate, titrate iodine with thiosulphate.
Determine valences for each species (half reactions) and prepare equinormal solutions of all, e.g. 0.1 N for all solutions. Now you know 1 ml of one
always corresponds to 1 ml of the others.
I know some find it confusing but they remind me of those Brits who still can't convert pounds to kilogram! |
Mols I get...................I am also a Brit so maybe thats why?
Dont ask me, I only know enough to be dangerous
|
|
|
DraconicAcid
International Hazard
Posts: 4334
Registered: 1-2-2013
Location: The tiniest college campus ever....
Member Is Offline
Mood: Semi-victorious.
|
|
I've met Brits who couldn't even convert stones to pounds. (They were selling tickets to use these human-sized hamster-ball things, but had a sign up
saying that you had to be under a certain number of stone to use one. They couldn't tell me how many kg that was, or how many pounds. It took me
five minutes to get them to decide if I was light enough to go in one.)
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
|
|
|
unionised
International Hazard
Posts: 5126
Registered: 1-11-2003
Location: UK
Member Is Online
Mood: No Mood
|
|
| Quote: Originally posted by blogfast25 |
They don't seem to teach normality all that much nowadays, which is a shame because in many reactive situations it is easier than molarity: 1
equivalent of whatever always reacts with 1 equivalent of whatever else.
[Edited on 17-11-2014 by blogfast25] |
Except when it doesn't.
For example, a solution of KMnO4 that is 1M is 5N if you are doing the titration in acid and 3N if you are doing it in base.
Good luck with things like peroxyacetic acid and formic acid.
They can be titrated as acids or as an oxidant and reductant respectively.
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
| Quote: Originally posted by blogfast25 |
No, no: you can't work normalities if you don't understand stoichiometry but in that case you can't do it with molarities either!...
|
I agree. I always use normality when doing titration calculations.
Yes, in practical every day usage 454g = 1 lb.
But technically, one unit is mass and the other is force! 
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
unionised
International Hazard
Posts: 5126
Registered: 1-11-2003
Location: UK
Member Is Online
Mood: No Mood
|
|
Well, in the foot pound second system the unit of force is the poundal so I guess you think that the kilogram is a unit of force.
Or is this the unit of force you meant
http://en.wikipedia.org/wiki/Slug_(mass)
|
|
|
aga
Forum Drunkard
Posts: 7030
Registered: 25-3-2014
Member Is Offline
|
|
Aside from the mathematical utility of Normality, it does make you think about the specific reaction more carefully.
Personally i found the use of Normality in a recent series of titrations a refreshing change, as there was no Normality around here before.
|
|
|
Etaoin Shrdlu
National Hazard
Posts: 724
Registered: 25-12-2013
Location: Wisconsin
Member Is Offline
Mood: Insufferable
|
|
| Quote: Originally posted by Magpie | | Quote: Originally posted by blogfast25 |
No, no: you can't work normalities if you don't understand stoichiometry but in that case you can't do it with molarities either!...
|
I agree. I always use normality when doing titration calculations.
Yes, in practical every day usage 454g = 1 lb.
But technically, one unit is mass and the other is force!
|
Except, in the US at least, the pound is also a legal unit of mass!
I got into a lighthearted argument with a lawyer over weight vs mass and was flabbergasted to learn this. Not that it doesn't make sense on some
level, it's just in the sciences I've always seen the pound as a unit of force and I've had it drilled into my head forever (with him it was the exact
opposite).
I think this is true in some international standard as well.
| Quote: Originally posted by unionised | Well, in the foot pound second system the unit of force is the poundal so I guess you think that the kilogram is a unit of force.
Or is this the unit of force you meant
http://en.wikipedia.org/wiki/Slug_(mass)
|
This one. http://en.wikipedia.org/wiki/Pound_(force)
[Edited on 11-17-2014 by Etaoin Shrdlu]
|
|
|
Little_Ghost_again
National Hazard
Posts: 985
Registered: 16-9-2014
Member Is Offline
Mood: Baffled
|
|
I am sorry I asked now
Dont ask me, I only know enough to be dangerous
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by unionised | Except when it doesn't.
For example, a solution of KMnO4 that is 1M is 5N if you are doing the titration in acid and 3N if you are doing it in base.
Good luck with things like peroxyacetic acid and formic acid.
They can be titrated as acids or as an oxidant and reductant respectively.
|
That's an old objection that's not exclusive to normality.
The specific reaction determines the valence used to calculate the equivalent mass of the species. When using molarities you need to take that into
account too. Someone who doesn't understand the reductions of permanganate in acid or alkaline conditions is likely to get it wrong, molarities or
normalities no matter. It's not a problem inherent to the idea of using equivalents instead of mol.
If you titrate H3PO4 with NaOH, which end point will you choose? Same problem, same easy solution: think before you begin, lest you end up getting it
wrong by a factor two or three.
The same is true for oxalic acid (as acid or reducing agent) and the other examples you bring up: If you don't even know what reaction you're using
them in you shouldn't be in a laboratory but in an embroidery course.
It's always been of these useless points of debate ('N v. M'): you gave some here something to bitch about, so don't worry! 
[Edited on 17-11-2014 by blogfast25]
|
|
|
aga
Forum Drunkard
Posts: 7030
Registered: 25-3-2014
Member Is Offline
|
|
Surely Molarity and Normality are both useful Tools to have in one's toolbox, so any argument about which is the Better Tool is utterly pointless ?
Just use the one that suits your situation best.
('situation' including which one you like best).
|
|
|
Little_Ghost_again
National Hazard
Posts: 985
Registered: 16-9-2014
Member Is Offline
Mood: Baffled
|
|
I confess when I first saw 1N on here I thought is was a typo  at least slowly I am
gaining knowledge. Every day I learn something new is a happy day
Dont ask me, I only know enough to be dangerous
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
