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# Percentage composition by mass of magnesium oxide

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Introduction

Lab report: Percentage composition by mass of magnesium oxide Introduction: Law of Definite Proportions is the law stating that a specific compound always contains the same elements in definite proportions by mass. We will experimentally determine the composition by mass of a substance and then convert he mass amounts to percentages, to give us the percentage composition. Magnesium is a silvery metal that burns with such a bright flame that it was once used in flashbulbs for photography. Magnesium oxide, a white powder, is produced as a result of the synthesis reaction of combustion magnesium. Hypothesis: The percentage composition by mass of magnesium oxide will be 60% magnesium and 40% oxygen. Purpose: To find the percentage composition by mass of magnesium oxide. Safety: * Wear eye protection. * Use crucible tongs to transfer hot crucible. * Care is required in using a lab burner and handling hot apparatus. * Magnesium ribbon burns with a hot flame and extremely bright light. Materials: Lab apron, eye protection, centigram or analytical balance, 7-8cm magnesium ribbon, steel wool, porcelain crucible and lid, lab burner, retort stand, ring stand and clamp, clay triangle, crucible tongs, glass stirring rod, distilled water. ...read more.

Middle

9. The crucible and its contents, with the lid slightly ajar, were heated gently for 3 minutes and then strongly for 7 minutes. 10. The crucible and contents were allowed to cool. 11. Using the balance, the mass of the cooled crucible, lid and contents were determined. Observations: Mass of crucible and cover Mass of crucible, cover, and magnesium Mass of crucible, cover and MgO Mass of Magnesium Mass of Oxygen 30.57g 30.70g 30.78g 0.13g 0.08g Calculations: 1. No. of moles of Mg = Mass of Mg = 0.13g = 0.00534mol of Mg Molar mass of Mg 24.3g No. of moles of O = Mass of O = 0.08g = 0.005mol of O Molar mass of O 16g Ratio of magnesium atoms to oxygen atoms is Mg : O :: 1.06 : 1 2. Total mass of Mg + O = Mass of Mg + Mass of O = 0.13g + 0.08g = 0.21g % of Mg in MgO = Mass of Mg x 100 = 0.13g x 100 = 62% Mass of MgO 0.21g % of O in MgO = Mass of O x 100 = 0.08g x 100 = 38% Mass of MgO 0.21g Discussion:: d) ...read more.

Conclusion

h) The magnesium ribbon was polished to remove any white film on its surface before beginning the experiment, explain why this is necessary. The magnesium ribbon was polished to expose the shiny part because this is the part of the magnesium that is reactive. Sources of Error:: * We only got to do the lab once because our magnesium ribbon took long to turn into white powder, so therefore, our results are not as accurate as possible. * The crucible may not have been thoroughly cleaned. * The flame was turning yellow on the Bunsen burner. Conclusion:: The percentage composition calculation for the magnesium in magnesium oxide, when calculated, worked out to 62% and the percentage composition calculation for the oxygen in magnesium oxide, when calculated, worked out to 38%. My hypothesis was that the magnesium would be 60% and the oxygen would be 40%. Therefore, my hypothesis was very close. In this lab, I learned how to calculate the percentage composition calculations and I can know relate the calculations to a real experience, which would make the concept of percentage composition more straight-forward and easier to understand. ...read more.

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