# Determine chemical reaction stoichiometry?

Unfortunately my background on chemistry is very weak but I have to do some experiments in that field as a part of my project.

Here is my problem: I am doing some leaching experiments on realgar (one of arsenic bearing minerals: $\ce{As4S4}$) I wanted to see how this mineral can be oxidized in water and arsenic can be leached out in different leaching conditions. However, I got confused about how I should write the chemical reactions related to my mineral oxidation and after that how I can derive stoichiometry coefficients related to my real conditions. Let say I have $\ce{AsS}$ ($\ce{As4S4}$) and based on my leaching conditions and Eh-pH diagram, I guess I have the following reaction: $$\ce{4 AsS + 9 O2 + 8 H2O -> 4 H3AsO3 + 4 SO4^2- + 8 H+}$$

After getting some samples I did ICP analysis and found that I have $2\ \mathrm{ppm}\ \ce{As}$ in my solution (which I think should be present in the form of $\ce{H3AsO3}$ based on the reaction). and saw that after a while this $2\ \mathrm{ppm}$ did not change significantly and we can say the reaction reached the equilibrium (roughly speaking) So, now can I derive stoichiometry coefficients based on these data or I should do something else?

• First of all welcome! Writing a chemical equation is definitely a good place to start when calculating stoichiometry. Have you tried that? Showing what you have tried, successfully or not, will help people to help you and they will be more motivated to do so when they see you have already made efforts to solve the problem yourself. – airhuff Jan 25 '17 at 21:17
• Thanks for the comment. I have edited my question :) Hopefully, it is now more clear :) – Elsa Jan 25 '17 at 22:27

## 1 Answer

This is really a long comment....

You're mingling several concepts in such a way that it is impossible to help you.

Stoichiometry is about balancing a chemical equation.

[Chemical] kinetics is about how fast a reaction occurs. There is scant correlation with stoichiometry. Kinetics is in general measuring how fast a reaction is moving towards equilibrium.

[Chemical] "Recovery," or extraction deals with what fraction of a particular element (or perhaps mineral) is recovered using a particular process. This again depends somewhat on kinetics but kinetics has a large number of factors. (So for Cu this would be what % of the Cu was extracted...)

Chemical equilibrium does depend on stoichiometry, but for an extration reaction a true equilibrium is rarely reached.