October 13, 2024, 12:20:17 PM
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Topic: Why does the Ion Equivalent vary between individual ions and ions in a salt?  (Read 7279 times)

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Offline dougjohnson

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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! :)

Offline fledarmus

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Not sure exactly what you're asking - the sulfate ion is SO42-, 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?

Offline dougjohnson

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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!!

Offline fledarmus

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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+ + SO42-

For every equivalent of MgSO4 dissolved, you get one equivalent of Mg2+ ions and one of SO42- ions.

For sodium sulfate,

Na2SO4 --> 2Na+ + SO42-

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

Offline vmelkon

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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.

Offline AWK

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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
AWK

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