Magnesium Oxide Laboratory Report

Abstract

The purpose of this experiment was to determine the percent composition by mass of magnesium in magnesium oxide and to compare the results with those of other groups to observe if the percentage composition is constant. The hypothesis was that the percent composition of magnesium in magnesium oxide would not change significantly among different groups, and any differences would be due to experimental errors. The experiment involved heating magnesium strips to form magnesium oxide, and the results were analyzed to draw conclusions about the law of constant composition.

Introduction

The law of constant composition, proposed by J.L. Proust, states that a compound always has the same percentage composition by mass, regardless of how it is prepared. In this experiment, we aimed to test this law by determining the percentage of magnesium in magnesium oxide and comparing our results with those of other groups. The class results were expected to validate or challenge Proust's theory.

Materials and Methods

The following materials were used in the experiment:

• Magnesium strip
• Crucible
• Crucible cover
• Clay triangle
• Iron ring
• Retort stand
• Tongs
• Balance
• Bunsen burner

The procedure consisted of the following steps:

1. Obtain a magnesium strip between 30-40 cm long.
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2. Coil the magnesium strip into a tight roll.
3. Measure the mass of the crucible and cover.
4. Add the magnesium strip to the crucible and measure the combined mass of magnesium, crucible, and cover.
5. Partially cover the crucible with the cover and heat it using a Bunsen burner until the magnesium ignites.
6. Turn off the Bunsen burner.
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7. Wait for the combustion to proceed.
8. When the reaction appears to be completed, heat the crucible again for another five minutes.
9. Allow the crucible to cool for ten minutes.
10. Measure the mass of the crucible, cover, and magnesium oxide.

Observations

During the experiment, several observations were made:

• When ignited, the magnesium strip emitted a bright light.
• There was a color change in the magnesium, starting as silver and turning into a white color.
• The combustion produced a distinct odor.
• The end result was a white powder, but some magnesium remained in its original shape.

The class obtained varying results for the percentage composition of magnesium in magnesium oxide. Some groups had similar values, while others had significantly different results. These differences raised questions about the law of constant composition.

Results

The experimental results for the percentage composition of magnesium in magnesium oxide varied among different groups. While some groups obtained values close to the expected theoretical value of 60.3%, others had results that deviated significantly from this value. The following table summarizes the results obtained by various groups:

Discussion

The class results revealed significant variation in the percentage composition of magnesium in magnesium oxide, with values ranging from 55.9% to 70.1%. These discrepancies raised questions about the validity of the law of constant composition, which asserts that a compound's composition remains constant regardless of its preparation.

One possible explanation for the observed variations is the presence of errors during the experiment. Several sources of error were identified. Mass loss during the experiment due to factors such as delayed ignition of magnesium, breaking of the magnesium strip, and incomplete combustion could have led to inaccurate results.

Another potential source of error is the incomplete combustion of magnesium, resulting in unreacted magnesium remaining in the crucible. This would lead to a lower total mass and, consequently, a lower percentage of magnesium in the compound.

Supporting French Scientist

The French scientist whose theory aligns with the experimental results is C.M. Berthollet. Berthollet proposed that a compound can have an infinite number of compositions depending on the proportions of the components used in its preparation. This theory supports the class results, which showed varying compositions of magnesium in magnesium oxide among different groups.

While J.L. Proust's theory, the law of constant composition, is widely accepted in chemistry, the experimental data suggests that the composition of magnesium oxide can vary depending on experimental conditions and errors. Therefore, in this case, Berthollet's theory seems to provide a better explanation for the observed results.

Sources of Error

Several sources of error were identified in the experiment:

• Mass loss during the experiment due to delayed ignition of magnesium, breaking of the magnesium strip, and incomplete combustion.
• Incomplete combustion of magnesium, resulting in unreacted magnesium remaining in the crucible.

Calculation of Actual Percentage

The actual percentage of magnesium in magnesium oxide was calculated using the molar mass of MgO:

Molar mass of MgO = 24.3 (Mg) + 16.0 (O) = 40.3 g/mol

For 1.00 mol of MgO:

%Mg = (24.3 / 40.3) x 100 = 60.3%

Therefore, the actual percentage of magnesium in MgO is 60.3%.

The percentage error for the group's result was calculated as follows:

% error = [(experimental - actual) / actual] x 100 = [(72 - 60.3) / 60.3] x 100 = 19.42%

Therefore, the percentage error for the group's result was 19.42%.

Conclusion

The experimental results obtained by different groups in the class suggested that the composition of magnesium oxide can vary depending on experimental conditions and errors. While the law of constant composition proposed by J.L. Proust asserts that a compound's composition remains constant, the class results did not fully support this theory. Instead, C.M. Berthollet's theory, which allows for varying compositions based on proportions, seemed to align better with the observed data.

It is important to acknowledge that sources of error, such as mass loss during the experiment and incomplete combustion, likely contributed to the variations in results. Therefore, the experimental data should not be used to challenge the well-established law of constant composition, but rather as a reminder of the importance of careful experimental technique to obtain accurate results in chemistry experiments.

Recommendations

Based on the sources of error identified in this experiment, the following recommendations are made to improve the accuracy of future experiments:

1. Ensure proper ignition of magnesium to minimize mass loss.
2. Take measures to prevent the breaking of the magnesium strip during handling.
3. Monitor the combustion process closely to achieve complete combustion of magnesium.