# Determining the Empirical Formula

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Determining the Empirical Formula of Magnesium Oxide Lab

Purpose The purpose of this lab was to determine the percent composition and empirical formula of magnesium oxide.

Hypothesis
If a strip of pure magnesium metal reacts with oxygen in the air to create magnesium oxide, then the molecular formula will be MgO. The percent composition for magnesium oxide would be 60.31% magnesium and 39.69% oxygen.

Apparatus Refer to attached sheet

Procedure
Refer to McGraw-Hill Ryerson Chemistry 11, page 212-213.

4. The mass of the empty crucible and lid was recorded. The strip of cleaned magnesium was added to the crucible. The mass of the crucible, lid and magnesium was recorded.
10. The substance remained in the crucible, above the flame for an extra five minutes on high heat, after the water had evaporated completely.

Results

Mass of clean, empty crucible and lid | 26.73g | Mass of crucible, lid, and magnesium | 26.87g | Mass of crucible and magnesium oxide | 26.95g |

Analysis
1.
a) We used 0.14 g of magnesium in the reaction.
b) 0.22 g of magnesium oxide was produced.
c) 0.08 g of oxygen reacted with the magnesium (0.22 g – 0.14 g = 0.08 g).
d) Refer to “Determining the Empirical Formula of Magnesium Oxide Lab Solutions” sheet
e)
Element | % | m (g) | M (g/mol) | n (m÷M) | ÷ by | Ratio | Magnesium | 63.63 | 63.63 | 24.31 | 2.617441382 | 2.273125 | 1 | Oxygen | 36.37 | 36.37 | 16.00 | 2.273125 | 2.273125 | 1 |
Since the ratio is 1:1, the empirical formula is MgO.

2. Refer to “Determining the Empirical Formula of Magnesium Oxide Lab Solutions” sheet

3. You need to round the empirical formula to a whole number ratio because you cannot have decimals in the subscripts, which means that you cannot have a fractional amount of molecules in a substance.

Conclusion

My hypothesis that the empirical formula for magnesium...

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