how would you calculate the EDTA normality, from weight and assay?

Molar mass = 292.24, normality = molarity, but EDTA must be properly dried which is not a trivial task (but perfectly doable given enough time and good lab dryer).

no!no!no!

Normality = molarity only for monoacids or monobase : NaOH or HCl can exchange only one proton

Normality is two time the molarity for diacids : sulfuric or malonic acids have two protons per molecules

So Normality of EDTA (ethylenediamineTETRAacetic acid have 4 protons) is four time higher than molarity (1 mol edta = 4 mol proton)

Molar mass = 292.24, normality = molarity, but EDTA must be properly dried which is not a trivial task (but perfectly doable given enough time and good lab dryer).

If you require it on assay, then divide weight by factor. For ex. If EDTA is 99% u require to weigh 292.24/0.99 g EDTA to prepare 1M -1000 ml solution.

Dear all,

EDTA always forms a 1:1 complex with metal ions. for this reason, its normality is equal to its molarity

I think we need to return to the definition of normality. I checked "Modern Analytical Chemistry; Harvey 2000":

The number of equivalents, n, is based on a reaction unit, which is that part of a chemical species involved in a reaction.

(Then, the book starts mentioning different types of reactions)

For a complexation reaction, the reaction unit is the number of electron pairs that can be accepted by the metal or donated by the ligand.

So, we can't just say that normality is molarity, as in our case EDTA might donate up to six pairs (and so the ligand binding to it would receive that much)...

Thanks all, correct me if I am mistaken

It seems I failed to explain the argument 

Even if it acts on one ion; we don't count by ions.

Where n is the number of reacting units.

The reference says we count by the number of reacting units --> in complexation reactions by the number of electron pairs...

let me give you a nice argument.

Consider the reaction of sulphuric acid with calcium hydroxide.

they react 1:1, but I don't think you can claim that normality of sulphuric acid is the same as molarity
Of course, normality will be DOUBLE that of molarity. (just multiply the molarity by the reacting units; here it's acid-base --> count the protons)

Normality of reactants depends on the reaction they take place in

I know; I was giving you an example from other type of reaction.

Can you cite me a reference saying how we count the reacting units in complexation reactions?

thanks a lot

determining Normality depends on the type of reaction

To determine normality, we have to count the number of reacting units (which MIGHT differ according to the reactions).

I went through more than 5 references and no one states what you say!

You just need to find a system to define normality... If you have a referenced one, then it's ok for me... but according to the definition I found in all the references I have, we count in complexation reactions the number of electron pairs...

I also think the discussion is going nowhere except if we:
1- succeed to find a definition for calculating normality in complexation reactions
2- apply that definition

I got the definition from my reference! You might have a different definition, for sure and then I would agree

and in the second phrase you state it doesn't (complexing agent normality doesn't depend on the reaction, depends only on the number of electron pairs)

According to reaction, you choose the way of counting reacting units... In acid-base --> protons; in complexation --> electron pairs; in redox --> electrons ... etc...

I don't think this takes us anywhere as well... Only because you can't reply in a better way respecting your opponent...

You may use this number in calculations but the results will be off.

I would suggest six for the other partner in the reaction as well. Notice that our difference is only VERBAL... I say 1 mol EDTA reacts with 1 mol calcium; corresponds to 6 N EDTA react with 6 N calicium (In that reaction; it's also 1:1). I am following a definition which won't affect the calculation cause in the very end they give the same result.

If we agree to call the Kg a "half-k" it won't be a problem at all with any calculation, as we generalize it...

For a complexation reaction, the reaction unit is the number of electron pairs that can be accepted by the metal or donated by the ligand.

That's the definition I got... Which goes for BOTH the EDTA and the one reacting with it. Of course, I don't mean that 6 N EDTA react with 2 N calcium (and I apologize if that what I managed to tell with my poor language). It goes for the donator AND the acceptor...

I asked the head of analytical chemistry department about this; how to calculate the normality of EDTA? she first told me that we don't need to calculate normality for EDTA as it reacts 1:1 then she said exactly what I stated

In this particular case it is molecule that is reacting unit

My friend, I don't mind this at all but it needs to be a convention known somewhere (that's why I asked for a definition or reference). If there is a reference saying so, or a convention following so, I really don't mind

You know, it's like 7 years ago when I argued about the definition of a "meter" in a physics class. The instructor laughed and said: "Define any meter you like, but others use another definition "

I am just afraid that conventionally the definition is different

Please understand that you can't use your references blindly, especially when they give simplified rules that contradict general definition.

Thanks for the advice. You might help me by giving me the general definition; may be I am mistaken. Please help me with this definition and mention the reference

This general definition, of course, should apply to all examples. It will really be helpful for me

Thanks a lot