Normality

[MedPR]

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Quantitatively, is normality just molarity*van't Hoff factor?

 

[SaintJude]

Not necessarily...

1 M sulfuric acid (H2SO4) is 2 N for acid-base reactions because each mole of sulfuric acid provides 2 moles of H+ ions. (where you're getting that conclusion from I suppose). So you could make that generalizations for strong acids in acid-base reactions, where they completely dissociate into their ions.

1 M sulfuric acid is 1 N for sulfate precipitation, since 1 mole of sulfuric acid provides 1 mole of sulfate ions.

 

[MedPR]

Not necessarily...

1 M sulfuric acid (H2SO4) is 2 N for acid-base reactions because each mole of sulfuric acid provides 2 moles of H+ ions. (where you're getting that conclusion from I suppose). So you could make that generalizations for strong acids in acid-base reactions, where they completely dissociate into their ions.

1 M sulfuric acid is 1 N for sulfate precipitation, since 1 mole of sulfuric acid provides 1 mole of sulfate ions.

So if I asked you what is the normality of a solution by mixing 50mL of 1.5M H3PO4 with 50mL H2O.

Would your answer be 2.25N H3PO4 (3N for 3H+) or 0.75N (1N for 1PO43-)?

 

[SaintJude]

Okay, so you are right, but only in solutions...

Normality = Molarity 👎 . Where n is the number of protons, hydroxide ions, electrons or monovalent ions (so PO43- doesn't apply) "produced" or "consumed" per molecule of the compound in any reaction. So I would say 2.25 N.

van't Hoff factor is related only to solutions. Definition by Kaplan is: van't Hoff facotr is "the moles of particles dissolved in a solution per mole of solute molecules". So that's why you can indeed say that Normality = molarity (i) for acid-base reactions for example, b/c they are conducted in aqueous solution.

At least that's how I understand. If I'm wrong...then I don't want to be right! Jk! correct me.😛

 

[MedPR]

Okay, so you are right, but only in solutions...

Normality = Molarity 👎 . Where n is the number of protons, hydroxide ions, electrons or monovalent ions (so PO43- doesn't apply) "produced" or "consumed" per molecule of the compound in any reaction. So I would say 2.25 N.

van't Hoff factor is related only to solutions. Definition by Kaplan is: van't Hoff facotr is "the moles of particles dissolved in a solution per mole of solute molecules". So that's why you can indeed say that Normality = molarity (i) for acid-base reactions for example, b/c they are conducted in aqueous solution.

At least that's how I understand. If I'm wrong...then I don't want to be right! Jk! correct me.😛

I wasn't trying to say you're wrong, I was hoping you could tell me how to know if I should use 3 because of 3H+ ions, or 1 because of 1PO43- ion..

 

[SaintJude]

Oh, but did the below makes sense?

Normality = Molarity 👎 . Where n is the number of protons, hydroxide ions, electrons or monovalent ions (so PO43- doesn't apply) "produced" or "consumed" per molecule of the compound in any reaction.

 

[MedPR]

Oh, but did the below makes sense?

Normality = Molarity 👎 . Where n is the number of protons, hydroxide ions, electrons or monovalent ions (so PO43- doesn't apply) "produced" or "consumed" per molecule of the compound in any reaction.

Yes and no. I know what you are saying, but I don't know if you are right for all situations.

mcat-review says

Normality = N = Molarity of the species that matter.
1 M HCl = 1 N HCl
1 M H2SO4 = 2 N H2SO4
1 M H3PO4 = 3 N H3PO4

So what you are saying about monovalent ions works for H2SO4 and H3PO4, but not for HCl. HCl makes 1 proton and 1 monovalent anion (Cl-) so you are saying it should have a normality of 2M, but mcat-review says 1M.

 

[SaintJude]

I think the convention is to only count either the number of protons or the monovalent ions. So that's why the definition still applies

"n is the number of protons, hydroxide ions, electrons or monovalent ions (so PO43- doesn't apply) "produced"

 

[MedPR]

I think the convention to only count either the number of protons or the monovalent ions. So that's why the definition still applies

"n is the number of protons, hydroxide ions, electrons or monovalent ions (so PO43- doesn't apply) "produced"

Oh, I missed the "or" 🙂 Ok thanks!