Verification of the Molecular Formula and Percent Composition of the Compound, Magnesium Oxide

Topics: Magnesium, Oxide, Magnesium oxide Pages: 6 (1886 words) Published: September 3, 2012
The Verification of the Molecular Formula and Percent Composition of the Compound Magnesium Oxide (MgO) Nice sounding title Date Performed Lab: 8/31/06

The purpose of this lab was to confirm the chemical formula of magnesium oxide by comparing the masses of pure magnesium solid prior to any reaction and magnesium oxide solid after a reaction between all of the magnesium and oxygen from the air when heated from a Bunsen burner in a crucible. Using molar masses of both magnesium and oxygen, an expected percent composition, by mass, was found and compared to our experimental results.

Find the mass of a clean crucible and cover. Add 8 inches of coiled magnesium ribbon to the crucible and mass again. Heat the crucible with cover slightly ajar and remove from heat when there is no more glow or shiny metallic pieces. Break up the remaining solid and add water. Heat the crucible to remove all water. Find the mass. good


Add magnesium in a clean crucible and heat the crucible with a small flame. Check the magnesium periodically and wait until the shiny appearances of the magnesium turn to grayish-white powdered oxide. Add water to the crucible and heat until the water is driven off; the expelled steam should make the pH paper bluish. Good and concise.

1. Initial weight of magnesium-

2. Weight of magnesium oxide present after reaction-

3. Percentage of magnesium in the magnesium oxide from experimental data- [pic]

4. Theoretical percentage of magnesium (by mass) in magnesium oxide- [pic][pic]

5. Percentage Error-
Nice looking calculations

In conclusion, we were able to confirm that the formula for magnesium oxide is MgO. Using the masses of Mg and MgO that we calculated from our experiment, we determined that the percent composition of Mg in MgO is 57.5937%. The actual percent composition is 60.304%. We had 4.4947% error.

By carefully applying heat and oxygen to a strip of pure magnesium, it was demonstrated that magnesium oxide was formed with magnesium and oxygen combining in a ratio of 1:1. The actual percentage composition of magnesium in magnesium oxide is 60.301% and experimentally we calculated a percentage composition of 64.1%. This supports the idea that elements in compounds combine in whole-number ratios. Good conclusion

Discussion of Theory:

One thing I want in discussion is for people to include the chemical equations within the discussion of theory as you talk about them.

Through this experiment we were able to confirm the formula of magnesium oxide. By using the data we gathered we were able to calculate the percentage of magnesium within our magnesium oxide. Upon comparing this to the theoretical percentage we found in the pre-lab, we proved that the formula of magnesium oxide is MgO.

We began our experiment by thoroughly cleaning and heat drying our crucible so as to remove any stray particles or trapped moisture. This was done to ensure that the weight of the crucible would remain constant to facilitate more accurate data collection. Throughout our experiment we were always sure to allow the crucible to return to room temperature before weighing it. Since the crucible is made of porcelain, a ceramic, it is a natural conductor. Thermal currents become insulated within the porcelain producing a slight lifting force on the crucible. This net upward force causes a reduction in the weight of the crucible that could affect the accuracy of our data. NICE! We then placed the magnesium in the crucible, covered it and proceeded to heat it carefully. Magnesium will generally oxidize at a very slow rate, however when it is heated this process occurs far more rapidly. We covered the crucible in order to limit the oxygen supply to magnesium and therefore control the reaction. In an uncovered crucible the reaction could occur too quickly and MgO would be...
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