COMPLETE THIS LABORATORY REPORT IS IN THIS DOCUMENT HIGHLIGHTED IN YELLOW ENTER YOUR ANSWERS AND INFORMATION IN THE LIGH

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COMPLETE THIS LABORATORY REPORT IS IN THIS DOCUMENT HIGHLIGHTED IN YELLOW ENTER YOUR ANSWERS AND INFORMATION IN THE LIGHT BLUE FIELDS Purpose The purpose of this experiment is to determine the empirical formula for magnesium oxide. Theory Many elements, when heated, will react with the oxygen gas (O2) that is present in air. The compounds that form contain the element and oxygen. These compounds are called oxides. As with all compounds the oxides that form have a definite composition. In other words, the mass ratio of oxygen to the other element in a compound is constant. For example water (H2O), which is obtained when hydrogen is burned in air, contains 88.8% oxygen and 11.2% hydrogen by mass. This ratio never varies. All samples of water have this percentage. In this experiment, you will heat a sample of magnesium in air to obtain magnesium oxide. The oxygen gas in the air will react with the magnesium in a specific ratio to give an oxide of definite composition. Mg(s) + O₂(g) magnesium oxide (s) You will determine the mass of your magnesium sample before heating and the mass of the magnesium oxide after the reaction is complete. The Law of Conservation of Mass states that the total mass of reactants and products must equal in a chemical reaction. mass of magnesium (Mg) + mass of oxygen gas (O₂) = mass of magnesium oxide Therefore, you can determine the mass of oxygen that reacted as follows.
You can calculate the empirical formula for the magnesium oxide with this information. An empirical formula is the smallest whole-number mole ratio of the elements in the compound. The empirical formula for the oxide can be determined by calculating the amount in moles of magnesium and atomic oxygen that combined in the reaction. The smallest whole-number mole ratio can be calculated from these numbers. The number of moles of magnesium and oxygen are calculated from the gram amounts as shown below. 1mole of Mg 24.3 grams of mass of Mg x- mass of O, x- 1mole of O₂ 2.0 grams of O, 32.0 Mg Materials Needed Magnesium ribbon (10 cm per student) X moles of Mg 2 moles of O 1mole of O, moles of O The ratio of moles of Mg to moles of O can be converted into the smallest whole- number ratio and used to determine the empirical formula of the compound. Procedure A. Preparation of a crucible I 1. Put on your chemical-splash safety goggles. Your goggles must be worn at all times while in the laboratory. Don't take off your goggles until you leave the laboratory. 2. Place a clean crucible and lid on a clay triangle supported by an iron ring. Adjust the height of the ring so that the bottom of the crucible will be in the hottest part of the Bunsen burner flame once the flame is lit. The hottest part of the flame is the tip of the inner cone. 3. Heat the empty crucible for 2 minutes. The bottom of the crucible should turn a dull- red color if you are heating the crucible properly. Allow the crucible and lid to cool after the 2-minute heating period. Cooling will take five to ten minutes. The top part of the Bunsen burner, the crucible, ring stand, iron ring and clay triangle will be very hot after heating. Do not touch these items with your hands until they have cooled
4. Determine the mass of the crucible and lid after it has cooled. Do not to place a hot crucible on the balance. Be sure to use the same balance for your other mass determinations in this experiment. B. Heating the magnesium 1. Obtain a strip of magnesium about 10 cm long. Fold the ribbon into a loose coll and place it into the crucible. Don't coil the magnesium ribbon too tightly. 2. Place the lid on the crucible and determine the mass of the crucible, lid and magnesium. Place the crucible on the clay triangle. Heat the crucible gently for two to three minutes. After two to three minutes of gentle heating, heat the bottom of the crucible in the hottest part of the flame. The bottom of the crucible should turn a dull- red color if you are heating the crucible properly. 3. Lift the lid of the crucible by a small amount using your crucible tongs to allow air into the crucible as you heat. Do this very carefully. The crucible lid is fragile and will probably break if you drop it. The lid will also be very hot. Do not open the lid too far, because doing so will cause the metal to catch on fire. The metal should glow brightly without producing flames. The metal will glow very brightly during this process. Do not look directly at the burning metal. Repeat the process of opening and closing the lid every two to three minutes until there is no more shiny, unreacted magnesium inside the crucible. At the end of the reaction the contents of the crucible should be a white or grey powder. 4. Allow the crucible to cool. Cooling will take five to ten minutes. Add 10 drops of distilled water to the oxide inside the crucible. Don't add water to a hot crucible. Place the crucible on the clay triangle and heat it in the hottest part of the flame for ten minutes. Determine the mass of the crucible once it has cooled. Don't place a hot crucible on the balance. 5. Clean all glassware and equipment that you used during this experiment and return it to its proper location. Clean your workstation and wash your hands with soap and water before you leave the laboratory.
DETERMINATION OF A CHEMICAL FORMULA Prelaboratory Assignment 1. You should not touch a hot crucible with your fingers or put a hot crucible on a balance. Approximately, how long does it take a hot crucible to cool down? Name Date 2. A sample of copper metal weighing 2.50 grams is heated in the presence of oxygen gas to form a copper oxide. After the reaction is complete, the final mass of the copper oxide is 3.13 grams. Complete the table below by answering the following questions. How many grams of copper reacted? • How many moles of copper reacted? How many grams of oxygen reacted? What is the empirical formula of the copper oxide based on the moles of copper (Cu) and the moles of oxygen (O) that reacted? . How many moles of oxygen reacted? (Calculate the moles of O not moles of Oz. See the Theory section.)
DETERMINATION OF A CHEMICAL FORMULA Data Sheet A. Preparation of a crucible Length of heating time for empty crucible and lid Mass of empty crucible and lid after heating Name Date B. Heating the magnesium Mass of crucible, lid, and unreacted magnesium Mass of empty crucible and lid (from Part A.) Mass of unreacted magnesium Length of heating time before addition of water Number of drops of distilled water added to magnesium oxide Length of heating time after addition of water Mass of crucible, lid, and magnesium oxide Mass of magnesium oxide 10.0 min 15.05 g 17.68 g 8.0 min 10 drops 10.0 min 19.41 g
DETERMINATION OF A CHEMICAL FORMULA Questions 1. Complete the table below by answering the following questions based on the data you collected during this experiment. How many grams of magnesium reacted? How many grams of oxygen reacted? Name Date What is the empirical formula of the magnesium oxide based on the moles of magnesium (Mg) and the moles of oxygen (O) that reacted? . How many moles of magnesium reacted? How many moles of oxygen reacted? (Calculate the moles of O not moles of Oz See the Theory section.)