Empirical Formula Determination Su18 151.pdf - Experimental...

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Chapter 10 / Exercise 105
Chemistry & Chemical Reactivity
Kotz/Treichel
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6-1 Experimental Determination of an Empirical Formula Name Date Lab Partner Because many elements have only one possible charge as an ion, it is easy to use theory to predict the molecular formula for an ionic compound. It is always good to be able to experimentally confirm the same results predicted by theory. Reproducible results are a hallmark of good science. The following experiment fits into the reproducible results category if you perform the experimental procedure carefully without large errors in data. Metals frequently react with atmospheric gases that are nonmetals. The main components of air are nitrogen and oxygen gas. It happens that both gases will react with the magnesium under the conditions of this experiment. To prevent the presence of the magnesium nitride and the difference in mass from causing an error in the final calculations, water is added to the mixed magnesium oxide/magnesium nitride product to drive off the nitrogen contaminant. The magnesium nitride is first converted to ammonia gas and solid magnesium hydroxide which, upon further heating, is converted into the desired magnesium oxide product. There are lots of detailed directions below. Follow them exactly or you may end up with horrible results or worse: a broken crucible or lid. If, at any point, you break the crucible or the lid or if you happen to spill any contents from the crucible, you would need to start over to get acceptable results. Be careful because each mass measurement can impact your final result. Record data in Tables and answer questions from pages 6-5 to 6 8. I. CONSTANT MASS DETERMINATION OF THE EMPTY CRUCIBLE Prior to using a crucible, you need to clean it and heat it to drive off any water or fingerprints. The technique of constant mass is utilized to ensure that this required initial condition has been met. Obtain a crucible and lid. Wash it with soapy tap water and gently use a brush. Rinse with tap water and then distilled water. Dry off any surface water with a Kim-wipe. Examine the crucible and lid for chips or cracks. If either is present, return it to the instructor and let them know about the damage. Practice picking up the crucible and lid (separately!) with the crucible tongs. After the first heating, you will not touch the crucible with your fingers again until the experiment is over and you are washing the crucible out. [Q1] Attach a ring clamp to a ring stand. Place the (unlit) Bunsen burner on the ring stand and adjust the ring clamp so that it is about 2 inches above the top of the Bunsen burner. Place a clay triangle on the ring clamp. Gently lower the crucible into the clay triangle. Do not let go of the crucible until you know the clay triangle supports it. (See Figure 1 on next page.)
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Chemistry & Chemical Reactivity
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Chapter 10 / Exercise 105
Chemistry & Chemical Reactivity
Kotz/Treichel
Expert Verified
6-2 Set the lid of the crucible onto the crucible slightly ajar. (Water vapor will need to escape via this opening.) You have the lowest risk of the crucible lid falling off if the non-supported part of the lid is centered over one of the clay triangle’s corners. Bring the Bunsen burner back

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