see above, something stupid I´ve always wondering about,
I know molar masses now, bur for confusion sake there´s a N *lol*. How do you calculate it?
thanks,
nightflightDarkblade48 - 13-6-2006 at 03:51
N represents normality; from Wikipedia:
Quote:
Normality is a measure of concentration: it is equal to the number of gram equivalents of a solute per liter of solution.
I've rarely seen concentrations using the N though, most often it's M or m (small M)
[Edited on 6-13-2006 by Darkblade48]garage chemist - 13-6-2006 at 07:35
Hmm, that definition is strange. I've always seen "N" as the number of moles of a substance in a Liter of solution. For example, a 4N NaOH solution
would then contain 4 mol NaOH per Liter.
But for molecules with two acidic or basic groups, it is the concentration of acidic or basic groups which is expressed.
For example, a 4N H2SO4 solution would contain only 2 mol H2SO4 per Liter since one mol of H2SO4 can neutralize 2 mol of OH ions.
Is that correct?Magpie - 13-6-2006 at 10:24
To reiterate:
N = normality = g-equivalents/liter
M = molarity = g-moles/liter
I've most often seen normality used when doing volumetric calculations in analytical chemistry. It simplifies the calculation, as then "normality
times volume equals normality times volume." Easy to remember.
(Na)(Va) = (Nb)(Vb)
where "a" = an acid and "b" = a base,
and V = the volumes used in the titration.
With this formula you don't have to worry about the acid being dibasic, tribasic, or whatever. I.e., you can titrate H2SO4 with NaOH and as long as
you have the right normalities the formula holds true.
Textbooks will often list the strength of common acids and bases in normality.Darkblade48 - 13-6-2006 at 12:26
Quote:
Originally posted by Magpie
Textbooks will often list the strength of common acids and bases in normality.
Really? All my textbooks seem to list the strength of common acids and bases in molarity How interesting.unionised - 13-6-2006 at 12:34
It's a real pig when you come to look at redox reactions.
A 1 M solution of KMnO4 can be N, 3N or 5N depending on the conditions and the reducing agent.
Even for an acid/ base reaction it can be complicated. If you titrate phosphoric acid with NaOH the volume you get depends on the indicator (IIRC
Methyl orange changes when the NaH2PO4 is converted to NaH2PO4. Thymolphthalein doesn't change untill you get Na3PO4) so the normality changes even
though the concentration is the same.
Generally, people seem to have stopped using normality.
(As an aside, Only in theworld of chemistry does it make perfect sense to stop dealing with normality)
How interesting.