the water drains from it into the leveling bulb, stopping when the water level reaches the lowest point visible in the pipette (point C). Attach and close screw clamp (D) tightly on the rubber tubing. Lower the pipette and reattach it to the ring stand. Check to see that no water comes into the pipette, which would indicate a leak. Nearly fill the leveling bulb with water. Make sure there are NO air bubbles in the rubber hose. Obtain a solid rubber stopper that fits the top of the pipette snugly, and place it next to your apparatus.
Mole Percent Oxygen in Air 2090 – © Cornell University (2019) 3 Figure 1 – Experimental apparatus. The main source of error in this experiment is not sealing the apparatus before the reaction starts. Be sure you have everything ready so you can move quickly in the next step! Using your funnel, pour 3 mL of 1M CoCl 2 (aq) solution into the pipette. Then, pour in 3 mL of 6M NH 3 (aq) (often labeled "NH 4 OH") solution, and immediately stopper the pipette firmly. Wait a few seconds for the solution on the walls to drain down, and then read and record the initial position of the upper level of the solution in the pipette. Carefully remove the pipette from the clamp on the ring stand and mix the reactants thoroughly by tipping the pipette back and forth. Then reclamp it to the ring stand. Allow the solution to react with the oxygen in the pipette for about 10 minutes (at least). Once every 2 minutes, loosen the pipette from the clamp on the ring stand and hold it nearly horizontally. Tip the pipette back and forth to allow oxygen to come into good contact with the solution. Do not vigorously shake the pipette. Reattach the pipette to the ring stand in a vertical position. Be sure to repeat the above step of thoroughly mixing the reactants every two (2) minutes! Slowly loosen the screw clamp, allowing the water to move from the leveling bulb through the rubber tubing into the pipette. Then remove the screw clamp from the rubber tubing. Adjust the level of water in the leveling bulb to match the level of the solution in the pipette by unclamping it from the ring stand and moving it up or down. When the water level in both the pipette and leveling bulb are the same, clamp the leveling bulb to the ring stand at that height. Under these conditions, the total gas pressure in the pipette will equal the barometric A B C D
Mole Percent Oxygen in Air 2090 – © Cornell University (2019) 4 pressure in the laboratory. Record the upper level of the solution in the pipette in your
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