EXPERIMENT 5: Properties of Gases Read the entire experiment and organize time, materials, and work space before beginning. Remember to review the safety sections and

EXPERIMENT 5: Properties of Gases Read the entire experiment and organize time, materials, and work space before beginning. Remember to review the safety sections and wear goggles when appropriate Objectives: To investigate some physical and chemical properties of gases, and To use these properties to identify these gases whenever they are encountered. Materials: Student Provides: Matches Toothpicks (or wooden splints) Pie tin or similar Drinking straw Household white vinegar 3% Hydrogen peroxide (H2O2) Measuring spoons Baking soda (sodium bicarbonate) From LabPaq: Goggles 24-well Plate 2 Test tubes Marker pencil From Aux. Chemical Bag: 6 M Hydrochloric acid (HCI) (To be diluted according to instructions) From Experiment Bag: 3 Wide-neck pipet bulbs 1 Pipet, Empty Short Stem Stopper w/copper & gas delivery tube Stopper w/plastic delivery tube Alka SeltzerR Mossy Zn pieces Manganese (Mn) pieces Bromthymol blue Limewater (saturated calcium hydroxide) Discussion and Review: Several gases are produced frequently in the laboratory and it is important to be able to identify them by their physical and chemical properties. The gases under investigation are hydrogen (H2), oxygen (O2), and carbon dioxide (CO2). These gases will be generated using small-scale techniques and carrying out the following reactions: Hands-On Labs SM-1 Lab Manual 56 Hydrogen (H2) Mg + 2HCl ¨ MgCl2 + H2 or Zn + 2HCl ¨ ZnCl2 + H2 Oxygen (O2) 2 H202 MnO2¨ 2 H2O + O2 Carbon Dioxide (CO2) NaHC03 + 2 HCl ¨ NaCl + H2O + CO2 PROCEDURES: 1. Hydrogen: A. Squeeze all of the HCl into a test tube. B. Place a small piece of Zn (mossy zinc) metal into the test tube containing the diluted HCI. C. Take the test tube and cap it with the rubber stopper with the short, straight, plastic gas delivery tubing through its center. Place the test tube into one of the wells of the 24-well plate. The test tube must stand up straight, so wrap a little tissue paper around the bottom of the test tube to wedge it upright into a well opening. Observe the reaction. D. Fill one wide-neck pipet bulb completely with water, invert and quickly place it on top of the test tube’s gas delivery tube as shown in the picture at right. E. Place the well plate with test tube assembly in a pie tin as some water will overflow when the water in the pipet bulb is displaced by gas. F. When the water in the collection pipet has been completely displaced with hydrogen remove the collection pipet, keeping it inverted, and quickly place a thumb over the opening to keep any gas from escaping. G. Light a match. While holding the hydrogen filled pipet bulb horizontally with its mouth about 1 cm from the flame, gently squeeze a small portion of the contents of the pipet into the flame and observe. H. Record your observations. I. With the marker pencil, mark the wide-neck pipet bulb on the outside into approximately three equal parts. Hands-On Labs SM-1 Lab Manual 57 J. Fill the marked pipet bulb with water, invert it, and set it onto the gas generation tube as before. K. When the bulb is filled 2/3 with gas remove it, still keeping it inverted, and set it with the opening facing down into one of the wells of the 24-well plate to be used later. K. Disassemble the test tube, pour the weak acid down the drain, and flush well with water. Dispose of the zinc fragment and paper towels in your trash can. L. Thoroughly rinse the test tube and rubber stopper assembly with water for use in the next section. 2. Oxygen: A. Place a few pieces of Mn (manganese) metal into the second test tube. B. Add enough 3% H2O2 (hydrogen peroxide) to fill the test tube to within 1 cm of the top. Place the rubber stopper with plastic gas delivery tube through its center into the test tube, and place the test tube into a well of the 24-well plate. Again, use some tissue to wedge it into a straight position. Observe the reaction and record your observation. How do the two reactions compare? C. Fill another wide-neck pipet bulb completely with water, invert and place it on top of the test tube’s gas delivery tube. D. When the water has been completely displaced with oxygen in the collection pipet remove the pipet and place your thumb over the opening to keep gas from escaping. E. Light a wooden toothpick, extinguish it and quickly, while it is still glowing, insert the toothpick into the oxygen-filled pipet. F. Record your observations. G. Give two reasons why we fill the gas generator test tubes almost to the top with chemicals. 3. Hydrogen and Oxygen Mixture: A. Take the collection pipet bulb saved from Part 1, which is partially filled with hydrogen, and place it on the oxygen generation test tube created in Part 2. B. Collect enough oxygen until all the water has been displaced. The bulb should now be filled with 2/3 hydrogen and 1/3 oxygen. Hands-On Labs SM-1 Lab Manual 58 C. Remove the bulb and place a thumb over the end to keep the gas mixture from escaping. D. Light a match. While holding the gas filled pipet horizontally with its mouth about 1 cm from the flame, gently squeeze the contents of the pipet into the flame and observe. E. Disassemble the test tube, pour the weak H2O2 solution down the drain and flush with water. Dispose of the manganese fragment and used paper towel in the trash. F. Thoroughly rinse the test tube and rubber stopper assembly for future use. G. Write a balanced equation for the reaction between O2 and H2. 4. Carbon Dioxide: Part 1: A. Put .5 to 1.0 mL of limewater into a well of the 24-well plate. B. Place half a teaspoon sodium bicarbonate (baking soda) in the bottom of the generation test tube. Hold the test tube over a pie tin or a sink and add half a pipet full of white vinegar to the sodium bicarbonate. As soon as the sodium bicarbonate and the vinegar are combined, they will react vigorously and some may overflow. That is all right. As soon as the overflow has stopped, insert the stopper with copper and plastic (c&p) gas dleivery tube into the test tube. C. Place the open end of the c&p gas delivery tube into the limewater previously placed in the well. D. What is happening to the limewater? Part 2: A. Put .5 to 1 mL of bromthymol blue into another well of the 24-well plate. B. Thoroughly rinse the gas generation test tube under running water in the sink and set up another test with sodium bicarbonate and vinegar as in Part 1 above. C. When the stopper assembly is in the test tube place the open end of the c&p gas delivery tube into the bromthymol blue. Observe and record the reaction. D. Remove the stopper and c&p gas delivery tube from the generation tube. Hands-On Labs SM-1 Lab Manual 59 E. Light a toothpick or match and insert the flame into the upper part of the gas generation test tube. F. Record your observation. Part 3: A. Pour the chemicals from the above experiments into a sink and flush with water. Then thoroughly rinse the test tubes, stopper, and c&p gas delivery tube for reuse. B. Put .5 to 1 mL of limewater into another well of the 24-well plate. C. Crumble the small piece of Alka SeltzerR tablet into the generation test tube. D. Add 1 pipet full of water to the Alka SeltzerR and then immediately insert the stopper with c&p gas delivery tubing into the generation tube. E. Place the open end of the c&p gas delivery tube into the limewater in the well. F. Observe and record the reaction. What does it mean? G. Thoroughly rinse the gas generation test tube under running water in the sink. Part 4: A. Place .5 to 1 mL limewater into a small test tube. B. Insert a straw and blow gently into it for a few seconds. C. What do you observe? Explain. D. Pour the limewater into a sink and flush with water. Part 5: Other: Make a table of the gases studied. Tabulate their colors, the effect on lighted or glowing splints, and other properties one might use to identify them. Cleanup: Flush remaining liquid chemicals down the sink and throw solid metals in the trash. Rinse and dry all equipment and store it for future experiments.

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