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Experiment: To Determine the Empirical Formula of Magnesium Oxide.

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September 12, 2003 Experiment: To Determine the Empirical Formula of Magnesium Oxide INTRODUCTION: The empirical formula is the simplest and lowest whole number ratio of the different atoms in a sample of compound. To work out the empirical formula, the value of moles of the different atoms in a compound is needed. Mole is just simply a unit used to measure the amount of atoms, just like how the unit "dozen" is used to measure things such as eggs. One mole is 6�10^23 atoms and this number is called the Avogadro number. The mole can be also defined as the number of atoms in exactly 12g of Carbon. In this experiment, the magnesium will be heated and this magnesium will react with the oxygen in the air to form magnesium Oxide. DIAGRAM: METHOD: 1. An empty crucible and its lid were weighed on an electrical balance. The mass of the crucible and its lid were recorded. 2. The surface of the magnesium ribbon was scraped with emery paper to remove any magnesium oxide on the surface. ...read more.


Mass of crucible and lid with magnesium (g) Mass of crucible and lid with magnesium oxide (g) 35.40 35.74 35.94 OUALATATIVE RESULTS: - White fume was coming out of the crucible, when the lid was lifted. - When the magnesium was first heated, the magnesium was glowing slightly orange, but it turned into a strong glow later. - Short after the magnesium had started to be heated, the magnesium turned black. However, as the reaction was beginning to finish, the magnesium became an ashy white color. CALCULATIONS: Mass of magnesium: Mass of crucible and lid with magnesium - Mass of empty crucible and lid 35.74g - 35.40g = 0.34g Mass of oxygen: Mass of crucible and lid with magnesium oxide - Mass of crucible and lid with magnesium 35.94g - 35.74g = 0.2g Moles of magnesium: Mass of magnesium Ar of magnesium 0.34g 24 = 0.014167 (6 D.P) Moles of oxygen: Mass of oxygen Ar of oxygen 0.2g 16 =0.0125 Mole ratio of magnesium : oxygen: Magnesium : oxygen 0.0141... ...read more.


Another way to prevent this error is to make sure that all the surface of the magnesium is touching the air. Unless all the magnesium is able to contact with the air that contains oxygen, not all of the magnesium will react. An additional possible source of error is that some white fume magnesium oxide escaped from the crucible. This error can be prevented by performing the experiment in a fume cupboard. The most significant source of error is that some magnesium possibly reacted with Nitrogen in the air to form Magnesium Nitride. Since 78% of air is made up of Nitrogen, it is highly possible that some Magnesium reacted with the Nitrogen. This made the mass of oxygen that reacted with the magnesium low, which made the mole of magnesium higher than the accepted value. This error can be prevented by burning the magnesium in pure oxygen, not air; although, this is very difficult to do in reality. One way the experiment can be improved is to perform the experiment several times and record the average result so that a more accurate result can be obtained. ...read more.

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