Handling Dry ice in a Grade School Setting The authors have twice been invited to present chemistry demonstrations a t a career fair forfifth graders a t a local elementary school. Among the substances demonstrated were dry ice and liquid nitrogen. Students of this age group have a n irresistible urge to touch the dry ice against good safety practice. The following procedure was developed to illustrate suhlimation, temperature effects on gas volume and condensation, all in a n environment of good safety. All the students and the demonstrators wore safety goggles. The program was held in the grade-school cafeteria with several other simultaneous presentations (map making, Greek cooking, archaeology, ete.). Students came to us in groups of 15 a t 20-min. intervals. Students were allowed to chose a party balloon (available in supermarkets) in their favorite colors. A piece of dry ice about one half centimeter cubed was placed by one of the authors in the balloon and the opening was tied off. The advantage of using a balloon is that the student is not likely to be burned by directly handling the cold dry ice. Thus, the student is able to hold the balloon and examine the dry ice within. The balloons were returned to the students who were able to make a number of observations on their own, such as "'It's cold!", "There is white stuff on the outside of the balloon!", "The ballaan is getting bigger!", *The piece of dry ice is getting smaller." etc. They then wanted to know what (or why something) was happening. Rather than directly answering their questions, we asked them to make deductions. For example, we asked them to touch the "white stuff', and when they did and the ice melted on their fingers, they discovered it was water, which led to a discussion of the mesence of water vaDor in the air around us. rhc students ubserved how quickly the balloon collapsed. When WL. plnrcd the bottom ofthe balloon in liquid'n~rrn~rn By rhnkmg the collnpird bnlloons, t h r s u d c n t s ubsen.rd the presence nfsol:d dry ire in the balloon. This proress was repeated n number of t m e s hy popular demand This appmach i n w h n g a handwm exercise u,as n 1 N C discovery pruresh on the p a n o f t h e students. The students were cxei~rd,which led t o n Ii\cly discussiun among them.+plveson rhr cNcrta they were uhderwng a i ehnngcs occurred tu thew halloonr. As an nddcd h n n m . the scudrnts were alluwed t o keep t h r hnllonna, rrinforcmg the learning procesa, and generating later discussion with other students not present Handling and Safety Precautions Since dry ice and liquid nitrogen exist a t very low temperatures under atmospheric pressure, burns can occur if these substances are not handled appropriately. While dry ice can be stored in a cardboard box prior to use, liquid nitrogen must he stored in a Dewar. I t must not be stored in a thermos or any container in which the cover fits tightly because of pressure build up. In addition, oxygen condenses in liquid nitrogen, creating another potential hazard. Although 78% of the atmosphere is nitrogen, suffocation may occur if these demonstrations are performed in small, airtight rooms; proper ventilation is required. Acknowledgment This paper is based upon work sponsored by the U.S. National Science Foundation under Grant Number: MR 87-51183. T o m a s G. Berger B., Edward K. Mellon, a n d William D. Bare The Florida State University Tallahassee. FL 32306
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Journal of Chemical Education
