I need help finding the empirical formula. Here is the data I collected during l

Question

I need help finding the empirical formula. Here is the data I collected during lab:

Mass of crucible and lid (g) - 31.408 g

Mass of crucible, lid, and sample of Mg (g) - 31.616 g

Mass of sample of Mg (g) - 0.208 g

I measured the sample after heating it and it turned to ash. It measured 31.763 g. A second measurement was required to find find out how much oxygen was in the sample afterwards. Water was added and heated and the was sample was weighed again. It measured 31.764 g. Because the measurements were within +/- 1%, 31.764 g was used. The new mass of the project was 0.356 g. This meant 0.148 g of oxygen was added during the experiment.

I know that the grams need to be changed to moles but I'm not sure how to do that and find the empirical formula.

Explanation / Answer

Mass of crucible and lid (g) - 31.408 g

Mass of crucible, lid, and sample of Mg (g) - 31.616 g

Mass of sample of Mg (g) - 0.208 g

So, mass of the sample of Mg (g) is =31.616- 31.408 =0.208 g

So, no of millimoles of Mg = 0.208/24 =8.66

As you have mentioned 0.148 g of oxygen was added during the experiment.
Millimoles of O =(0.148/16)*1000 =9.25

So, the ratio of Mg :O is =8.66/9.25 =0.936

Thus, the empirical formula is =(Mg)0.936O

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