Do not touch these items without first trying to feel for heat being radiated off them without touching them. DO NOT look directly into the crucible while it is being heated! DO NOT place anything hot directly onto the lab bench, always place hot objects on a heat resistant mat. DO NOT place anything hot on a balance!
Clean a 35 mm strip of magnesium about 0. Wind the magnesium strip around a clean glass stirring rod to obtain a loose coil and place this inside the crucible and place the lid on the crucible.
Weigh the crucible, lid and magnesium remember not to handle the crucible with your hands, use tongs. Using tongs, place the crucible on the pipe clay triangle and position the lid so that it is slightly off-center to allow air to enter but prevent the magnesium oxide from escaping. Light the Bunsen Burner, and obtain a blue flame, and use this flame to brush the bottom of the crucible for about 1 minute until the magnesium starts to burn as evidenced by a bright glow within the crucible, then place the Bunsen Burner under the crucible and heat strongly until all the magnesium turns into a grey-white powder about 10 minutes.
Use tongs to re-position the lid so that it covers the crucible. This is done to prevent contaminants from the air, especially water, from entering the crucible while it is cooling.
While still on a blue flame, slide the Bunsen Burner out from under the crucible before turning it off to prevent soot attaching to the crucible. Allow the crucible to cool to room temperature while still on the pipe clay triangle.
Use tongs to re-position the crucible back into the pipe clay triangle with the lid slightly off-center as before, and heat strongly for a few more minutes. Remove the Bunsen Burner, and allow the crucible to cool back to room temperature, then weigh the crucible and lid again.
Continue this heating, cooling and weighing process until you achieve a constant mass. Take the test now! Calculate the mass of magnesium used in the experiment: Calculate the mass of magnesium oxide produced: Calculate the mass of oxygen present in the magnesium oxide: Calculate the moles of magnesium present in the magnesium oxide compound: Calculate the moles of oxygen present in the magnesium oxide compound: Calculate the mole ratio magnesium: Write the empirical formula for the magnesium oxide: We have calculated that the ratio of moles and hence the ratio of number of atoms of Mg to O in magnesium oxide is 1: If the mass of magnesium oxide is too high Contamination is the most likely problem.
Water may have entered your crucible while it was cooling especially if your lid was not completely covering your crucible , or soot or other particulate matter may have adhered to the top, sides, or lid of your crucible. If the mass of magnesium oxide is too low. Magnesium oxide product is a very fine powder which can easily escape whenever the lid on the crucible is raised.
Consider, if you lost just 0. The mass of magnesium oxide will also be too low if some of the magnesium metal does not combust. Consider an experiment in which 0. Competing Reactions 6 Air contains not only oxygen gas but also a large proportion of nitrogen gas. Although nitrogen gas is not particularly reactive, magnesium is a very reactive metal, and, at the temperatures achieved during the combustion of magnesium some magnesium will also react with nitrogen gas, that is:.
If about half of the original 0. Our final "magnesium oxide" product would contain 0. We can calculate how much MgO would be included in the product:. The apparent mass of "magnesium oxide" product would therefore be 0. O would be 0. Magnesium oxide is best thought of as an ionic compound containing magnesium ions and oxide ions.
So, strictly speaking we should not talk of magnesium atoms and oxygen atoms in this compound, nor should we talk of a molecule of magnesium oxide because a molecule refers to a compound in which atoms are covalently bonded to each other. However, in order to keep the explanation as clear as possible, we shall refer to "atoms" and "molecules".
In order to save time in class, it is quite likely that your crucible has already been prepared for you. You should still be aware of how this is done and why.
Alternatively you can place a pipe clay triangle over a tripod in a "star of David" formation. You may need to use a heat resistant mat or tiles under the Bunsen Burner to maintain the correct position. It is better to cool the crucible in a dessicator to remove any moisture, however, in a school laboratory it is not advisable for students to be walking around with hot crucibles, so either keep the crucible in the pipe clay triangle, or, remove the hot crucible using tongs and place it on a nearby heat resistant mat to cool.
If time is limited, it is possible to light the magnesium strip inside the crucible and quickly position the lid using tongs before heating the crucible. However, it should be noted that some magnesium oxide will probably be lost as the fine powder quickly escapes from the crucible before the lid is positioned. It is possible to heat the crucible containing the magnesium without the lid in order to start the combustion of the magnesium, then replace the lid very quickly, repeating this several times until all the magnesium has been converted to magnesium oxide.
This method works well to convert the magnesium to magnesium oxide, but once again, while the lid is off the crucible some of the fine-powdery magnesium oxide tends be lost. The magnesium nitride can be converted to magnesium oxide to remove this source of error.
Here is a video that illustrates how to determine an empirical formula. Related questions How do empirical formulas and molecular formulas differ? How do you find molecular formula of a compound? What is the chemical formula of a diamond? What is the chemical formula of a carbohydrate? What is the empirical formula for valproic acid? Why is the empirical formula not double that of the monosaccharides? What molecular formula represents a carbohydrate? What is the molecular formula of vinegar?
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Assume that you heated g of magnesium and obtained g of the oxide. What is the empirical formula of magnesium oxide? Solution. The empirical formula is the simplest whole-number ratio of atoms in a compound. The ratio of atoms is the same as the ratio of moles. So our job is to calculate the molar ratio of #"Mg"# to #"O"#.
Magnesium is reacted with oxygen from the air in a crucible, and the masses before and after the oxidation are measured. The resulting masses are used to calculate the experimental empirical formula of magnesium oxide, which is then compared to the theoretical empirical formula.
Empirical Formula of Magnesium Oxide by Experiment Chemistry Tutorial Key Concepts. Empirical formula of a compound gives the lowest whole number ratio of atoms of each element present in the compound. Empirical formula of magnesium oxide is determined by reacting magnesium metal with oxygen from the air to produce the magnesium oxide. magnesium nitride to magnesium oxide. Thus, the final product of the synthesis will be pure magnesium oxide. Using calculations similar to those presented in Example 2, you will determine the empirical formula of the magnesium oxide product.
Theoretical empirical formula of magnesium oxide = MgO Trial 1 To obtain the empirical formula MgO, the mole ratio of magnesium to oxygen should be 1 to 1, hence the theoretical mole of oxygen should be equal as the mole of magnesium = mol. Determining the Empirical Formula of Magnesium. Oxide Intro The empirical formula of a substance is the simplest whole number ratio of the number of atoms of each element in the compound.3/5(2).