Law of Constant Composition Lab: Magnesium and Oxygen

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Purpose: To determine the percent magnesium by mass in magnesium oxide and to observe if the percentage composition is constant by comparing class results.

Hypothesis/Prediction: The percent composition by mass of magnesium in magnesium oxide will not change significantly with each group that conducted the experiment. The composition of each substance should stay the same and any differences must be due to some error.

Materials:Magnesium stripCrucibleCrucible coverClay triangleIron ringRetort standTongsBalanceBunsen burnerProcedure:1.obtained a strip of magnesium between 30-40 cm long2.coiled magnesium strip into a tight roll3.measured the mass of the crucible and cover4.Added the magnesium strip to the crucible and measured the
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For all three of our own individual groups trials, we obtained the same percentage composition and this satisfies Prousts theory.

This is also accurate with what we have read in the textbook Chemistry 11 on the Law of Definite Proportions on pages 147 150.

2.What conclusion can you make upon the class results?The conclusions I can make based upon the class results are that the composition of a compound must vary because everyone had a different answer. In most cases, the percent composition of magnesium in the compound was very different from what my group achieved. However, sometimes, the classes results were quite similar to my own.

The theory that C.M. Berthollet introduced about the composition of a compound was that a compound has an infinite number of compositions depending on the proportions of the components that were used in its preparation. His theory satisfies the results obtained from the whole class. Since every group had a different amount of magnesium they must also have had a different composition of magnesium in the compound formed, magnesium oxide.

However, this is inconsistent with what we have been taught and with what is written in the textbook. Since the textbook is a more reliable source of information, I must conclude that the reason for this difference in results may be attributed to error on the part of the students conducting the experiment.

3.Which French Scientist would you tend to support? Explain.

The French scientist that I

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