[dougjohnson]

Hey,
I was wondering if anyone could explain why the ion equivalent would vary from an individual ion, for example sulphate has a 2 mole equivalent as an individual ion, whereas, as an ion in magnesium sulphate it has an ion equivalence of 1 mole...
Any help would be really appreciated!

[fledarmus]

Not sure exactly what you're asking - the sulfate ion is SO₄^2-, and the magnesium ion is Mg²⁺ - hence, the neutral salt would be MgSO₄. The sodium ion, on the other hand, is Na⁺, so the neutral sodium sulfate would be Na₂SO₄. Magnesium sulfate would give you one equivalent of magnesium ions and one equivalent of sulfate ions, while sodium sulfate would give you two equivalents of sodium ions and one of sulfate ions.

Is this anywhere close to what you were asking?

[dougjohnson]

Thanks, somewhat, however I found information in a chemistry textbook stating that as an individual electrolyte Sulphate has an ionic equivalent of 2 moles of charge and the same applies to Magnesium, however in magnesium sulphate both ions have an ionic equivalence of 1 mole respectively...
Could this simply be due to the ionic bonding or am i missing the point?
Thanks again!!

[fledarmus]

Ah - I think you are confused about the concept of equivalents. Not surprising, it doesn't get used very consistently and most sub-specialties of chemistry have their own unique definitions depending on the type of chemistry they are doing. In general, however, the equivalents are referring to the numbers in front of the components of a balanced reaction.

Some examples - in your case, the number of equivalents of a sulfate or magnesium ion is how many of those are formed when your magnesium sulfate is dissolved:

MgSO₄ ---> Mg²⁺ + SO₄^2-

For every equivalent of MgSO₄ dissolved, you get one equivalent of Mg²⁺ ions and one of SO₄^2- ions.

For sodium sulfate,

Na₂SO₄ --> 2Na⁺ + SO₄^2-

One equivalent of Na₂SO₄ dissolved will give you two equivalents of sodium ions, but only one of sulfate ions.

[vmelkon]

Thanks, somewhat, however I found information in a chemistry textbook stating that as an individual electrolyte Sulphate has an ionic equivalent of 2 moles of charge and the same applies to Magnesium, however in magnesium sulphate both ions have an ionic equivalence of 1 mole respectively...
Could this simply be due to the ionic bonding or am i missing the point?
Thanks again!!

For sulfate, they probably mean that if you have 1 mole of SO4, then the charge is "2 moles of charge".

I haven't seen it expressed that way. Normally, textbooks say that the charge of a single SO4 is 2-.

A magnesium ion is 2+. How many Mg per SO4? I think that is obvious.

[AWK]

Equivalents are used to simplify and minimization of number of operations in stoichiometry calculation. They are used for reducing all equation coefficients of the chemical reaction to unity. In most cases equivalent corresponds to one mole of  molecules, unitary charges of ions or exchanged electrons. But in some cases there is no need to use this definition, eg in the reaction
MgSO4 + BaCl2 = = BaSO4(s) + MgCl2 we have unit coefficients without using above definition (we just use moles).

Hence when dougjohnson think about general definition equivalent then he should use
  one mole of sulfate ions = two equivalent of sulfate ions
but for above reaction
 one mole of sulfate ions = one equivalent of sulfate ions

Note these exclusions from general definition are used only for actual reaction