When do you use normality?

[MTD52]

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How do you know when you have to use normality and not just molarity? I know how to convert from molarity to N, but I'm not sure when you have to.

I got a problem dealing with a titration of NaOH and HCl. I forgot to use N, but in this case it didn't matter because both are the same as their respective molarities.

Anyway, how do I know when to apply it?

 

[Kneecoal]

if it were Ba(OH)2 instead, there you would multiply the molarity by 2, because you have 2 OH's

 

[nze82]

Whenever the reactive species (i.e. H+, OH-) has a coefficient other than 1.

 

[UCB05]

Normality is a pretty facetious term to differentiate solute molarity and reaction-specific equivalency, and can be completely ignored if you factor label correctly.

How do you know when you have to use normality and not just molarity? It completely depends on the question. Take Ba(OH)2. Its normality is 2x in an acid-base reaction (2 -OH per molecule), 3x in a colligative property question (3 ions per molecule), 1x in a simple displacement reaction involving the Ba+2 ion (1 Ba+2 per molecule), 2x in a redox reaction with Ba+2 (2 e- per Ba+2)

I wouldn't bother with sweating the details on normality unless the question explicitly asks using that term. Just use some common sense and figure it out based on the reaction in the question.

 

[MTD52]

Thanks guys. Normality is just (M)*(#dissociated OH or H), right?

 

[BiomajorPreDent]

Yes

Also, its common to use normality in titration problems, whereas most dilution problems you just use molarity, what everyone else said is dead on

 

[UCB05]

Thanks guys. Normality is just (M)*(#dissociated OH or H), right?

For an acid/base titration, yes.

 

[MTD52]

Thanks guys.