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CHEM 121: The Ideal Gas Law Lab Name: Partner(s): The Ideal Gas Law (PV = nRT) relates all four of the bulk properties of gases (pressure, volume, temperature and amount). In order for these relationships to be formalized into a law, a constant (R) must be included to reconcile the units of the four variables. The numerical value for R, then depends on the units for pressure and volume. In this lab we will use mm Hg and liters (L) for our units, and hence the value for R is: R=62.4 mm Hg L/mol K In this experiment, you will measure the volume of gas produced from a chemical reaction at room temperature and ambient atmospheric pressure. You will then relate this experimental volume to the theoretical volume using the balanced chemical equation. Magnesium metal reacts with hydrochloric acid to produce hydrogen gas according to: Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) Since we will run the reaction with excess acid, the amount (mols) of hydrogen gas produced should be equal to the amount (mols) of magnesium used. We can compare this theoretical volume with the actual (experimental) volume of gas to evaluate the success of our experiment. 1. Cut a piece of magnesium ribbon about 3.5 cm long. Record the exact mass of the magnesium in your data table. 2. Fill a large beaker about 3/4 full with tap water at room temperature. 3. Add deionized water to the gas collection tube until it is completely filled. 4. Hold your finger over the open end of the gas collection tube. Invert it and put the open end into the beaker of water so that it is about 3 cm submerged. Remove your finger from the open end of the tube. Use a ring stand and buret clamp to hold the collection tube in place. 5. Insert a piece of soft rubber tubing into the open end of the gas collection tube. Connect the other end to the port of a small side-arm Erlenmeyer flask. 6. Use a graduated cylinder to measure 8.0 mL of 6 M HCl. Add the HCl to the side- arm flask. Find a stopper that fits securely in the side-arm flask.
7. Quickly add the magnesium strip to the acid in the side-arm flask and immediately stopper the flask. 8. While the reaction is taking place, fill a large graduated cylinder with tap water. 9. When the reaction is complete, carefully remove the soft rubber tubing from the gas collection tube and hold your finger over the open end. Submerge the open end of the gas collection tube into the graduated cylinder. Once it is underwater, it is safe to remove your finger. 10.Keeping it under water, adjust the gas collection tube so that the water inside the gas collection tube is lined up with the water inside the graduated cylinder. (This ensures the pressure of gas inside the collection tube is equal to the atmospheric pressure.) 11. When the water levels are lined up, read the volume of gas in the collection tube and record it in your post lab. 12.Record the atmospheric pressure in your post lab. 13.Measure the temperature of the water in the graduated cylinder and record it in your post lab. 14.Empty the water into the sink. Empty the acid in the side-arm flask into a waste beaker. Rinse the side-arm flask several times into the waste beaker. 15.Repeat the entire procedure a second time. To get the best results, you must re- record the temperature and pressure. Waste treatment: Test the pH of your waste beaker. 1. Use a tiny square (no more than 1 cm long) of pH paper. If the pH is between 5 and 7, the solution can be poured directly down the drain. 2. If the solution has a pH less than 5, add sodium bicarbonate in small amounts until it stops fizzing. After it stops fizzing, the entire solution can be poured down the drain. 3. If the solution has a pH greater than 7, add vinegar in small amounts and swirl or stir after each addition. Continue testing the pH until it can be poured down the train. Table 1: Gas Constant Lab Data, Trial #1 Trial #2 Mass of magnesium used Volume of gas produced 0.0699 bbb mL 0.0719 65.9mL
Temperature of water 23.4°C 23.5°C Atmospheric Pressure (from 1014 mh 1016 mb barometer) Results 1 in Hg RI. Convert atmospheric pressure into mm Hg. 1013 mb= 760 mm Hg = 25.4 mm Hg Trial #1 Trial #2 R2. Convert the volume of hydrogen gas in the test tube into liters (L). IL-1000 mL Trial #1 Trial #2 R3. Convert the temperature of the water in K. K= °C+273 Trial #1 Trial #2 R4. Calculate the amount of magnesium in mols. (molar mass of Mg = 24.3 g) Trial #1 Trail #2 R5. Using the mol amount of Mg (above), calculate the theoretical volume of hydrogen gas using the Ideal Gas Law (V = nRT/P) Trial #1 Trial #2
R6. Using the formula below, calculate a % difference for each volume measurement. (experimental volume-theoretical volume) theoretical volume % difference = x 100 Trial #1 Trial #2 R7. Average the two % difference values and record this value here R8. How well did your experiment work? Explain. Reflection Questions: 1. What was the purpose of the lab? 2. What two pieces of equipment were used and what were they used for? 3. What did you learn by completing the lab?