Recently I have started in a new microbiology lab, and with a new lab come new habits. When I was working with my bacterial (liquid) culture next to the flame (Bunsen burner) wearing nitrile gloves, my colleague warned me to not wear gloves close to the flame. Personally, I never experienced any problems with them and I think that wearing them provides better sterility.
Is it more dangerous to work with gloves close to the Bunsen burner than without?
new microbiology lab
What're the entry requirements for your lab? If you're working in BSL-2 or greater, the appropriate PPE ensemble is listed and required at all times while you're in there. Likewise, gloves are required whenever you're in contact with potentially infectious materials (OSHA 29CFR1910.1030). There shouldn't be leeway to decide when and when not to wear your PPE ensemble.
As bunsen burners do present a burn hazard, your work with a bunsen burner should be preceded by general lab safety training, and subject to work practice controls. It's safe to wear nitrile gloves working with an open flame, and your gloves are not readily combustible. Burns will typically result from a failure to exercise universal precaution and/or use the burner properly.
If you're working dangerously close to an open flame or with heated materials, consider controlling for injury with thermal gloves, tongs, or engineer out the burner with a biosafety cabinet.
Wearing gloves increases the risk of injury when working next to an open flame since they can melt onto your hand.
Not wearing gloves increases the risk of infection when working with pathogens.
As for sterility, standard examination gloves may be helpful but are not necessary. The gloves aren't packaged sterile, you don't use sterile technique when putting them on, and nothing you touch with them is sterile.
So, whether or not you wear gloves near a flame really depends on what you're doing and the safety requirements of your laboratory.
The Science of Popcorn
Popcorn is one of the world’s favorite snack foods. In the US, Americans consume as much as 18 billion quarts of popcorn each year, which equates to 56 quarts per person. Some nutritionists call it a perfect snack food because it is a whole grain, a good source of fiber, and low in fat. One study even claims there are more antioxidants in popcorn than in some fruits and vegetables. 1
The most intriguing part of popcorn is the science behind how it pops. Popcorn is the only grain in the corn family that pops open when exposed to temperatures above 180° C. A popcorn kernel is composed of 3 parts: the pericarp, germ, and endosperm. See Fig. 1.
The pericarp is the tough outer shell surrounding a popcorn kernel, and the key to what makes it pop. Inside the pericarp is the germ, or seed embryo. Adjacent to the germ is the endosperm, which contains some trapped water plus soft and hard starch granules that serve as food for the germ when it sprouts.
When a popcorn kernel is heated, the trapped water in the endosperm turns into steam, building up pressure inside the pericarp. This pressurized, super-heated steam transforms the soft starch in the endosperm into a gelatinous material. Popcorn pericarp is much stronger than that of all other corn kernels and is able to retain this pressurized steam up to 9.2 atm (135 psi).
Above that pressure, the pericarp ruptures, releasing the steam and gelatinous starch that solidifies upon cooling. The resulting popped kernel is 40 to 50 times its original size. To see popcorn pop in slow motion, select from the Pop Videos menu, “Popcorn in Slow Motion” 2 .
|Figure 1 Corn kernel.|
People often wonder what is the ideal percentage of water in popcorn kernels for best popping. Popcorn is harvested in the fall when the kernels’ moisture content is between 16 and 20%. The kernels are then stored in bins where they are dried by forced air until reaching an optimum moisture level of 14%. If the moisture content drops below that value, the size of the popped kernels is smaller and the number of kernels that pop decreases.
- Determine the % of water by weight for 20 kernels of each brand.
- Determine the internal pressure in atmospheres (atm) needed for each of the 20 kernels to pop. Hint: Use the ideal gas law, PV = nRT. Solve for P, which will be pressure in atm.
- n = Moles of water lost (g water lost after popping ÷ 18.0 g/mol)
- R = Ideal gas law constant (0.0821 L-atm/mol•K)
- T = Boiling temperature of cooking oil in Kelvin (225° C + 273) = 498 K
- V = Volume of 20 kernels (determined by displacement of 5 mL water in a 10- or 25-mL graduated cylinder.)
Materials (for 30 students working in pairs)
- 15 Beakers (250 mL)
- 15 Graduated Cylinders (10 or 25 mL)
- 15 Wire Gauzes
- 15 Ring Stands (with iron rings)
- 15 Bunsen Burners or Hot Plates
- 15 Weighing Boats
Students should wear goggles and aprons or lab coats during the activity and exercise due caution around Bunsen burners or hot plates. Inform students that cooking oil boils at a higher temperature than water (225° C) and have them cover their beakers with aluminum foil to contain the popping corn and boiling oil. Note: Remind students not to eat any of the popcorn produced in the lab.
- Students should add just enough oil to cover the bottom of their beaker before adding the 20 kernels of popcorn.
- Mass 20 kernels in a weighing boat and subtract out the weighing boat’s mass.
- Mass the beaker, oil, and 20 kernels before heating and without the foil covering.
- Mass the room temperature beaker, oil, and popcorn after heating and without the foil.
Mass of 20 kernels + weighing boat
Volume of popcorn (5.0 mL water displaced to 6.5 mL)
Mass of beaker, oil, and kernels
Mass of beaker, oil, and popped popcorn at room temperature
Moles of water lost = 0.20 g ÷ 18.0 g/mol
- % of water in kernels = water lost ÷ mass of kernels × 100
Conclusion/discussion of errors
Most literature cites popping pressure as 9.2 atm (135 psi). If you choose to give your students that value, have them look at their measurements and see where some weaknesses may lie. An obvious weakness is the number of popcorn kernels. The more kernels used, the more accurate the measurements for volume and loss of water will be due to more significant digits. The temperature of the boiling oil is assumed to be 225° C, and the kernels are assumed to all pop at the same temperature.
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Popcorn is a great real-world example and science phenomenon to use when discussing the kinetic molecular theory of gases, the phase change of water from a liquid to a gas, Gay-Lussac’s gas law (pressure directly related to temperature), Charles’ law (volume and temperature directly related), or the ideal gas law (PV = nRT). After covering the KMT and gas laws in class, complement the lesson with a student-designed inquiry activity using several brands of popcorn, both bag and microwave varieties to examine and explain the phenomenon of popping corn.
When a popcorn kernel is heated, the trapped water in the endosperm turns into steam, building up pressure inside the pericarp to more than 9.0 atm. This pressurized, super-heated steam transforms the soft starch in the endosperm into a gelatinous material. The pericarp ruptures, releasing the steam and gelatinous starch that solidifies upon cooling. The resulting popped kernel is 40 to 50 times its original size. The optimum moisture level for popcorn is 14%, below that value, the size of the popped kernels is smaller and the number of kernels that pop decreases.
A clear workspace prevents accidental ignition of objects such as books, papers and science experiment materials. Set up the Bunsen burner on a solid, flat surface to avoid tipping. Keep the flame away from any combustible materials. Gather all of the necessary materials for the experiment before lighting the flame so you don't have to leave it unsupervised. Have your lighter or striker ready so you can light the flame as soon as you turn on the gas to the Bunsen burner. If others are in the lab with you, let them know you are lighting a flame.
A Bunsen burner allows you to control the flame by adjusting the collar that controls air flow. The flame needed varies by experiment, so find out that information before you put anything over the lit burner. Tongs allow you to safely hold items over the flames. Follow the experiment steps exactly, using the flame only as indicated to avoid injury or explosion. When you are finished with the flame, shut it off completely, ensuring that the gas valve is completely shut off. Allow the Bunsen burner and any items held over the flame to cool before touching them.