In this lab, you will be making hydrogen gas and oxygen gas and making bubbles from various mixtures of the two to try to find the ideal mixture. The two gases will be mixed in a syringe and injected into bubble solution to make bubbles filled with the mixture. The bubbles will then be lit with a lighter.
Safety-
Hydrochloric acid is very dangerous to the skin and eyes. Wear goggles at all times and rinse skin thoroughly if contact is made. Hold the syringe facing up at all times so that if pressure is released, HCl will not be sprayed out. The small explosion can be loud and you should protect your ears. It also may splash the bubble solution around, so keep your papers away. Hydrogen produces very little flame, so as long as directions are followed exactly, there is no danger from the flame.
Procedure-
For this lab, you will need to produce a syringe full of oxygen as we have done before and a syringe full of hydrogen as explained next. Produce 50-60 mL of hydrogen gas by reacting .07 mg of magnesium with 8 mL of 1.0 M HCl. When the reaction is complete, point the syringe upward and remove the cap. Point the syringe downward into a neutralization tank and release the excess liquid.
Press the syringe plunger down until it is at the 50 mL mark. For the data to work out properly, you must start with 50 mL. Get a plastic weighing boat and fill it half way with bubble solution. Inject 10 mL of the hydrogen gas through the bubble solution to make a small mound of bubbles. Protect your ears, move all of the papers away, and ignite the bubbles. In your data table, note the relative loudness of the bang. The loudness is directly related to the completeness of the reaction.
For each time that you release 10 mL of the gas, you will replace it with 10 mL of oxygen and repeat the bubbling and igniting. In doing this, you will be decreasing the percentage of hydrogen and increasing the percentage of oxygen each time. You are attempting to find the stoichiometrically correct ratio of hydrogen to oxygen. Repeat this procedure until your oxygen is gone.
Pre-Lab Questions-
1. Write the balanced equation for the combustion of hydrogen. (Hint: the only product is water)
2. From your balanced equation, in 10 mL of gas, how many mL would be hydrogen and how many would be oxygen in a perfect stoichiometric mixture?
3. Calculate what percent each of the mixtures that you will be making are hydrogen. (For example, trial #1 is 100% H2, trial #2 has 40 mL H2 and 10 mL of O2 = 80% H2. Trial number 3 is .80(40)= 32 mL of H2 (64%) and 18 mL of O2 (36%))
Have these percentages in your data table before you come to lab.
Post-Lab Questions-
1. Prepare a chart with a column for the percent H2 and the relative loudness of the explosion.
2. With which mixture did you get the loudest bang?
3. How did your actual answer compare to the theoretical answer (pre-lab #2)?
4. How do you explain your answer to #3?
Questions? Comments??
Mike Horton