PROCEDURES

1.Obtain a 100 mL graduated cylinder, a 600 mL beaker, a 18 mm x 150 mm test tube, an adjustable barrel clamp, a thermometer, and a tubing stopper combination. Set up the hydrogen generator shown in Figure 10.1 as follows. Stop up the sink with a #8 rubber stopper, and fill the sink ~3/4 full with water. Immerse the 600 mL beaker and 100 mL graduated cylinder in the sink, filling each completely with water.

2. Invert the filled 100 mL graduated cylinder, and insert it into the 600 mL beaker. .

3. Remove the 600 mL beaker and 100 mL graduated cylinder together, and carefully pour enough water out of the beaker until there is only ~350 mL of water in the beaker. Be careful when pouring the water that you do not allow air to enter the inverted graduated cylinder. Place the beaker and graduated cylinder arrangement on several paper towels next to the ring stand. Place the curved open glass end of the tubing assembly into the beaker filling the open end of the tubing with water. Carefully pick up the inverted, filled, graduated cylinder, and set it over the open end of the glass tubing. Do not allow air to enter the graduated cylinder during movement.

4. Attach an adjustable barrel clamp to the ring stand, and adjust it to a 45 degree angle relative to the ring stand pole. Tighten the barrel so the clamp will stay at the 45 degree angle. Adjust the height of the clamp to approximately 12 cm above the bench top. Obtain 8 mL of 6 M HCl(aq) in a clean 25 mL graduated cylinder. Carefully pour the HCl(aq) into the test tube. Securely clamp the test tube in the prepared clamp.

5. Obtain a clean pre-cut piece of Zn metal, which should have a mass between 0.180 and 0.230 g. Weigh the Zn in a weighing boat or weighing paper, and record the appropriate mass on the data sheet.

6. Obtain a 1/4 pie shaped piece of 5.5 cm filter paper. Wrap the weighed Zn metal in the filter paper. Thoroughly wet the wrapped Zn, and then squeeze out any excess water.

7. Carefully insert the wet, wrapped Zn approximately 1 inch into the test tube so that it clings to the side of the test tube. Do not allow the Zn to fall into the HCl(aq) during insertion! Securely insert the stoppered end of the tubing arrangement into the test tube.

8. Tap the test tube clamp with an ink pen or pencil until the vibration causes the wrapped Zn to fall into the HCl(aq). Do not hit the test tube directly with the pen or pencil, since the test tube may break!

9. After the Zn falls into the HCl(aq), it should react according to Equation 5 producing H2 gas. The gas will bubble into the inverted graduated cylinder displacing the water. Hydrogen evolution should last 10 - 20 minutes.

10. After H2 gas evolution has ceased, carefully lift the inverted graduated cylinder and remove the glass tubing from the beaker. Do not allow air to enter the graduated cylinder during movement.

11. Carefully transfer the beaker and graduated cylinder together into the sink filling only the beaker with water. Again be careful not to allow air to enter the graduated cylinder during movement. While holding the graduated cylinder, lower the beaker to the bottom of the sink. Carefully adjust the inverted graduated cylinder in the sink until the water level in the cylinder is the same as the water level in the sink. This adjustment makes the pressure of the trapped gas mixture equal to atmospheric pressure.

12. When the two water levels are the same, read the volume of the trapped gas mixture to one decimal place using the scale on the graduated cylinder. (Remember that since the cylinder is inverted, the scale will be upside down.) Record the three significant figure volume of H2 gas generated on your data sheet.

13. Remove the graduated cylinder from the sink, and vent the H2 gas into the hood. The vapor pressure of water may be obtained from Appendix B (by interpolation). Obtain the atmospheric pressure from the barometer and record it on the data sheet.

14. Measure the temperature of the water in the sink to one decimal place, not ending in zero, and record it on the data sheet.