Determination of an Empirical Formula Lab, Lab Reports of Chemistry

Download Determination of an Empirical Formula Lab and more Lab Reports Chemistry in PDF only on Docsity! Determination of an Empirical Formula PRELAB Use your textbook to answer the following questions about empirical formulas: 1.) What is an empirical formula? 2.) How can you use the percent composition of a compound to determine its empirical formula? 3.) If the empirical formula is different than the molecular formula, how are the two related? 4.) If you know the empirical formula of a compound, what other information do you need to determine the molecular formula of the compound? 5.) Make a flow chart of how to calculate an empirical formula from mass data. I. PURPOSE In this experiment, you will use mass relationships to determine the ratio in which 2 elements combine. II. MATERIALS crucible and cover ring stand iron ring clay triangle crucible tongs scissors burner balance dropper pipet stirring rod magnesium ribbon III. PROCEDURE 1. Carefully inspect a crucible and cover for cracks and chips. If your crucible has any, bring it to your teacher for inspection and possible replacement. Wash and dry your crucible and cover. Now, heat the assembly over the burner for 2 to 3 minutes to remove any excess water in the porcelain. 2. Let the assembly cool and weigh the crucible only. 3. Cut about 30cm of magnesium ribbon into about 1cm pieces. Put the magnesium into the crucible and weigh the crucible and magnesium. 4. Cover the crucible and place the assembly in the clay triangle. Heat for 2 minutes with a low flame. Using the crucible tongs, tilt the cover to let air into the crucible and heat strongly for 10 minutes (bottom of crucible should be red). 5. Remove the crucible cover and let the crucible and contents cool. 6. Weigh the crucible and contents. 7. With a dropper pipet add 3 or 4 drops of water and mix with the stirring rod and note the odor with care. CAUTION: Gently waft fumes to nose and inhale slowly. Do not inhale deeply. IV. DATA Record your data in a chart of your own design. V. CALCULATIONS 1. Calculate the mass of magnesium. 2. Calculate the mass of oxygen that reacted with the magnesium. 3. Calculate the number of moles of magnesium. 4. Calculate the number of moles of oxygen. 5. Calculate the mole ratio of magnesium to oxygen. (#3/ #4) VI. QUESTIONS 1. What is the formula for magnesium oxide based on your calculations? Is this the same formula you would expect given the charge on magnesium and oxygen ions predicted by the periodic table? 2. What is the ratio of mass of magnesium to oxygen? Why is this ratio different than the ratio in calculation #5? 3. What do subscripts in a formula tell us about atoms? Moles? 4. How can you explain the odor of ammonia when you added water to the material in the crucible? 5. Does the ammonia odor have any bearing on the results of this experiment? 6. Suggest a change in procedure that would help this problem with ammonia? VII. DISCUSSION OF ERROR Clearly state a possible explanation of why your calculated mole ratio is different than what you would predict using the periodic table.