Definition of Normality

[JReiss]

So I know the molarity of 1 M sulfuric acid is equal to 2, b/c there are 2 protons released (diprotic acid). However I recently heard that 1M MgCl2 has a normality equal to three. Also Fe(OH)3 has a normality equal to 4. Can anyone explain how that could be?

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[MT Headed]

The definition of normality is "moles of crap that I care about, per liter of solution", in units of (mol crap / L soln).

With one molar sulfuric acid, the crap that you care about is probably the acidic protons. You have two moles of protons for every one mole of H2SO4.

With MgCl2, the crap you are probably more concered with is the total number of ions running around in solution. In this case there are three moles of ions for every one mole of MgCl2.

Normality really depends on context.