Tracking of oxygen molecules in glucose oxidation
I think this experiment (PDF file) will help you understand the basic concept about the fate of oxygen in aerobic respiration. Basically the result is:


The oxygen of respiratory carbon dioxide is in exchange equilibrium with body water.
Utilized molecular oxygen is converted to body water. 


In respect to calculation of electrons donated to oxygen, just calculating how many NADH2 and how many FADH2 is reduced in how many steps during ETC will be able to answer your question.