Determination of the Chemical Formula of Magnesium Oxide

Abstract: The purpose of this lab was to determine the empirical formula of magnesium oxide by experimental means. In this lab magnesium ribbon was cooked in a cleaned crucible with a cleaned lid (that was weighed). After it was cooked distilled water was then added to it to remove all of the nitrogen that was created. After all of the water was cooked out of the magnesium, magnesium oxide was left behind. After all of the proper weighing and calculations were completed the empirical formula was determined. As a result it was found that the empirical formula was MgO.

Results and Discussion: After the experiment was finished, moles were calculated for the magnesium and the oxygen to find that the formula was MgO. Compared with the standard values the calculations were correct and matched what the formula should be. One source of error could have been that the magnesium was not fully cleaned which would have left oxidation on it and caused false results. Another source of error could have been sitting the crucible out over night until the experiment could have been finished the next day. By doing this the magnesium ashes could have absorbed more water or air born particles.

Answers to Questions:

Suppose a student transferred the crucible containing the magnesium oxide and the lid to the scale with his/her hands after it had cooled. What effect could this have on the calculated ratio of moles of magnesium to moles of oxygen, Mg:O? Justify your answer.

1.This could have made the weight rise a little because of the oils/dirt on your hands wasn't calculated so that would be added to the total weight of the magnesium and then when it was time to find the oxygen later it wouldn't be the right amount because you accounted for more magnesium than you really had.

Suppose a student allowed a significant amount of white smoke to escape while heating the ribbon. What effect would this have had on the calculated moles of oxygen? Explain.

2. Lots of the oxygen would have escaped and the weight would have changed.

A

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