[Fenrir]

Hi guys,

It might be a somewhat dumb question, but I was wondering how you convert a weight % of an oxide compound to the element weight %, for example:

MgO (30%) --> Mg (?)

I have several measurements containg only MgO, or only Mg, but I need both to put them in a statistical database for deriving a model. I thought it could be as easy as just looking at the molar masses of both Mg and O, and look for the relative weight of each of these in the whole compound, but I'm not entirely sure.

Thanks in advance and greetings from the Netherlands.

E.

[Borek]

Mg has 100% of Mg.

[Fenrir]

Mg has 100% of Mg.

That I do understand 
Maybe I was not entirely clear, but my question is how to convert a MgO weight % in a melt to Mg weight % in a melt, and other way around, if you know the value of one (for example 30 weight % of MgO in a melt, how much Mg weight % would be in the melt? ).

In the dataset, during some experiments only Mg weight % was; some only measured MgO weight %, so I would like to make both columns complete in order to make a certain statistical analysis.

[Arkcon]

OK, you know how much Mg weighs, but in MgO, its "adulterated" if you will, with a fixed ratio of oxygen.  Can you determine oxygen's weight, and the compute?

[Fenrir]

That sounds logical, but then some weird things occur in a certain (un)published dataset on olivine-melt trace element partitioning;
in a certain synthesized melt a MgO wt% measurement of 30,85% was measured, and a Mg wt% of 6,71%.. In another experiment a MgO wt% of 24,37 and Mg wt% of 5,30 was measured.

I don't get how these differences can be that large. I would expect a ratio of these wt% values of MgO and Mg respectively of  40,31/24,305 = 1,658.. But that does not seems to be the case.

[Borek]

[tex]\frac{5.30}{24.37} = \frac{6.71}{30.85} = 0.2175[/tex]

These numbers are identical within 0.01% accuracy.

What is interesting is the fact that they are quite different from the Mg% in MgO.

[MarkHolland]

Molecular weights of some oxides and factors to convert them to elements by weight.
---------------------------------------------------------------------------------

Oxide    Mol. Wt.    Factor
Al2O3    101.96128    0.529251
As2O3    197.89    0.7574
Au2O    409.93    0.9610
B2O3            69.6182      0.310551
BaO           153.3394    0.895660
BeO           25.01158     0.360320
CO2           44.0098      0.272916
CaO          56.0794      0.714701
CeO2    172.1188    0.814089
Ce2O3    328.2382    0.853770
CoO            74.9326    0.786483