How to calculate of the number of monocationic millimoles? If I have concentrations of: $SiO_2$, $TiO_2$, $K_2O$, $MgO$, $MnO$, $Na_2O$, etc.

How can I get $Na^+$, $Mg^{2+}$, $Mn^{2+}$ ..?

This is part of an intent to calculate the weathering intensity scale suggested by Meunier et al. (2013), but it is a doubt suitable to any kind of use of oxides, so post it apart from it. See a related WIS question.

Reference: Meunier, A.; Caner, L.; Hubert, F.; El Albani, A. and Prêt, D. (2013). The weathering intensity scale (WIS): An alternative approach of the Chemical Index of Alteration (CIA). American Journal of Science, 313(2), p.113-143. doi: 10.2475/02.2013.03

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    $\begingroup$ Since you posed the question here, do you have a background for the question that more directly relates it to earth science? As it stands, it seems it might fit better in the chemistry site better. Not saying for sure it doesn't belong here, but would be good to get some background of where your values are coming from, what you're trying to do, what course it's for, etc $\endgroup$ Nov 3 '17 at 18:08
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    $\begingroup$ @JeopardyTempest I edited the question, but if you can improve it in order to get it answered I will be very grateful. $\endgroup$ Nov 6 '17 at 14:02
  • $\begingroup$ Start here: encrypted.google.com/… $\endgroup$
    – Gimelist
    Nov 8 '17 at 10:14
  • $\begingroup$ @Michael : sorry but no, it is not what I'm looking for. Here I want to know about monocationic elements of oxides (i.e. how many $X^+$,$X^{2+}$,etc. are in $X_nO_m$). $\endgroup$ Nov 8 '17 at 12:39
  • $\begingroup$ Please specify where exactly your problem is. You have some masses or moles of the compounds stated above ($SiO_2$, $TiO_2$, ...). (a) First, calculate the moles of Si, O, Ti, ... per compound. (b) Then, sum the cations with + and 2+ individually. Do I miss a step (c)? Seems to be straight forward. $\endgroup$ Nov 9 '17 at 9:09

Oxygen is always divalent negative. An oxide has to be charge balanced, meaning the total has to be zero.

  • Therefore, some like CaO means you have Ca2+O2-.
  • Something like SiO2 is going to be Si4+2O2-.
  • Something like Na2O is going to be 2Na+O2-.

As you can see, the charges all sum to zero, given that oxygen is negative two.

Let's work out an example:

You have 1 moles of each: K2O, MgO, and ZrO2. You will have one mole of Mg2+, one mole of Zr4+, and two moles of K+.


Rock chemical analysis can be expressed as oxides, and I think this is what you are asking about. Since there are two moles of monoatomic cation per mole of oxide, multiply the molar oxide concentration by 2.


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