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 magnesium, crucible and cover together.

5.Partially covered the crucible with the cover and heated it using a Bunsen burner until the magnesium ignited.

6.Turned off Bunsen burner.

7.waited for combustion to proceed8.when the reaction appeared completed, heated the crucible again for another five minutes9.allowed crucible to cool for ten minutes10.measured the mass of the crucible, cover and magnesium oxideObservations:When ignited, the magnesium strip gave off a bright light.

There was a colour change on the magnesium.

It started out as silver and turned into a white colour.

The combustion gave off a distinct odour.

The end result was a white powder but some magnesium had been left in its original shape.

Individual Group ResultsTrial No.Mass of Crucible and CoverMass of Crucible, cover and MgMass of Crucible, Cover and MgO133.8834.7735.12233.8834.7735.12333.9134.8035.15Class ResultsTrial No.Mass of Crucible and CoverMass of Crucible, cover and MgMass of Crucible, Cover and MgO436.6137.3934.83533.9134.6634.92633.5734.3434.28733.7934.5235.12832.8034.6134.83935.6136.3936.631032.8033.5734.37Analysis and Interpretation:Calculations1.Calculate the mass of the magnesium used.

Mass = Mass of Crucible, cover and Mg Mass of Crucible and CoverTrial No. 1 Mass = 34.77 33.88= 0.89Trial No. 2 Mass = 34.77 33.88= 0.89Trial No. 3 Mass = 34.80 33.91= 0.89Trial No. 4 Mass = 37.39 36.61= 0.78Trial No. 5 Mass = 34.66 33.91= 0.75Trial No. 6 Mass = 34.34 33.57= 0.77Trial No. 7 Mass = 34.52 33.79= 0.73Trial No. 8 Mass = 34.61 32.80= 1.81Trial No. 9 Mass = 36.39 35.61= 0.78Trial No. 10 Mass = 33.57 32.80= 0.772.Calculate the mass of the magnesium oxide.

Mass = Mass of Crucible, cover and MgO mass of Crucible and CoverTrial No. 1 Mass = 35.12 33.88= 1.24Trial No. 2 Mass = 35.12 33.88= 1.24Trial No. 3 Mass = 35.15 33.91= 1.24Trial No. 4 Mass = 34.83 36.61= -1.78Trial No. 5 Mass = 34.92 33.91= 1.01Trial No. 6 Mass = 34.28 33.57= 0.71Trial No. 7 Mass = 35.12 33.79= 1.33Trial No. 8 Mass = 34.83 32.80= 2.03Trial No. 9 Mass = 36.63 35.61= 1.02Trial No. 10 Mass = 34.37 32.80= 1.573.calculate the percentage by mass of Mg in MgO% Mg = mass of Mg / mass of MgO x 100Trial No. 1 %Mg = 0.89 / 1.24 x 100= 72%Trial No. 2 %Mg = 0.89 / 1.24 x 100= 72%Trial No. 3 %Mg = 0.89 / 1.24 x 100= 72%Trial No. 4 %Mg = 0.78 / -1.78 x 100= -44%Trial No. 5 %Mg = 0.75 / 1.01 x 100= 74%Trial No. 6 %Mg = 0.77 / 0.71 x 100= 108%Trial No. 7 %Mg = 0.73 / 1.33 x 100= 55%Trial No. 8 %Mg = 1.81 / 2.03 x 100= 89%Trial No. 9 %Mg = 0.78 / 1.02 x 100=76%Trial No. 10 %Mg = 0.77 / 1.57 x 100= 49%The following table shows the mass of Magnesium alone, magnesium oxide alone and the percentage by mass of magnesium in the compound for each trial.

Trial No.Mass of MgMass of MgO% mass of Mg in MgOIndividual Group Results10.891.2472%20.891.2472%30.891.2472%Class Results40.78-1.78-44%50.751.0174%60.770.71108%70.731.3355%81.812.0389%90.781.0276%100.771.5749%Discussion1.What conclusion can you make about the composition of magnesium oxide based on your data?The conclusions I can draw from our own groups results are that Magnesium makes up 72% of the magnesium oxide compound and therefore, oxygen must make up the...
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