Percentage composition by mass of Magnesium oxide

Essay by pragi4ever May 2005

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The purpose of this lab was to test the law of definite proportions for the synthesis reaction of combusting magnesium. In this lab, the polished magnesium ribbon was placed in covered crucible and was heated in order for it to react with Oxygen presented in air and in water provided. The result showed that Magnesium oxide formed through chemical reaction was made up of 60.19% magnesium and 39.81% oxygen, which is approximate proportion of both particles in every Magnesium oxide compound. From this lab it can be concluded that the law of definite proportion stating that the elements in a pure compound combine in definite proportion to each other is factual.


The law of definite proportion states that every chemical compound contains definite and constant proportion (by weight) of its constituent elements. The purpose of this lab was to test for law of definite proportion through determining percentage composition of each element in Magnesium oxide.

I hypothesized that the composition mass of magnesium will be more than oxygen and this would be the result for other groups as well. My null hypothesis was that if the experiment is done accurately, the percentage composition of magnesium shouldn't exceed 65%.


-Refer to lab manual on page 180 in Nelson Chemistry 11.

-The following revisions were made:

-Nickel crucible and lid was used instead of porcelain crucible and lid

-Tripod was used instead of retort stand, ring stand and clamp


1. The nickel crucible and lid were cleaned and dried.

2. The observations about appearance of magnesium ribbon were made.

3. The magnesium ribbon was polished and rolled using pen in order to fit it in crucible.

4. As directed the mass of the crucible, magnesium ribbon and lid was measured. The total mass of all tree components...