In the Classroom edited by
JCE DigiDemos: Tested Demonstrations
Ed Vitz
Kutztown University Kutztown, PA 19530
Using Hydrogen Balloons To Display Metal Ion Spectra submitted by:
checked by:
James H. Maynard Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706;
[email protected] Wayne Wolsey Department of Chemistry, Macalester College, St. Paul, MN 55105
In a previously published demonstration (1), balloons containing metal salts are inflated with hydrogen and ignited to dramatically exhibit metal ion flame colors. We have optimized the procedure to yield the brightest possible flash while minimizing the quantity of airborne combustion products and made air quality measurements in a lecture hall immediately after the demonstration. While we recommend that this demonstration be done outdoors or in a hood, the results show that contaminants do not exceed maximum allowable concentrations in a well-ventilated, large lecture hall. Materials Hydrogen gas (cylinder or chemical generator) Matches or lighter Flame wand with tubing and source of methane, natural gas, propane, or candle and meter stick Cotton string or twine Metal nuts or other weights to tie to the balloons 2 g each of LiCl, SrCl2, CaCl2, CuCl2, KCl, NaCl Mortar and pestle, one for each metal ion salt Several balloons Droppers for each metal ion salt Several spatulas Ear plugs or noise muffs Safety gloves (nitrile or latex) Labels and marker Methanol, 1–2 mL per balloon Deionized water 1–2 mL per balloon Natural gas supply or propane supply, if using flame wand Candle, optional to re-light wand if blown out
Preparation Balloons should be prepared just before use. Place about 2 g of metal salt in mortar and powder with the pestle. Add approximately 1 mL of deionized water and 1 mL of methanol to the mortar.1 Mix the slurry with the spatula or draw liquid into a dropper and discharge back into the mortar several times to facilitate mixing. Draw approximately 1 mL of the slurry into a dropper and squeeze it into an uninflated balloon. Inflate the balloon with hydrogen and agitate the balloon for not more than a few seconds to spread the slurry thinly throughout the interior surface. The unused slurry can be stored in small polyethylene screw-top bottle.
from the audience. Use a flame wand (burner or candle on a meter stick) to ignite balloon near the bottom. A colored fire ball with a diameter of about 1 m will result (Table 1). This demonstration is best performed in the dark. Hazards Methanol and some metal chlorides are toxic so protective clothing, gloves, and eye protection should be worn at all times. A fire extinguisher must be on hand. Students should be warned about the noise associated with the explosion, and the demonstrator should wear ear protection. Toxic salts (for example, those of nickel, arsenic, and barium) should not be used, nor should salts other than chlorides be used, especially in the presence of methanol. Flush waste solution down the sink, with plenty of water, or in the case of heavy metals, precipitate the metal cation, filter, and dispose of in solid metal waste container. Air Quality Measurements The air quality data2,3 were obtained when the demonstration was presented at this university (2). Detectors were placed at two different locations in the lecture hall.4 Conditions were adjusted to minimize air flow, that is, closing the doors and turning the lectern vent fan off. The data indicate that particulate matter airborne after the demonstration is below personal exposure limits for said species, where data exist. The federal levels for particulate matter under 10 μm in diameter (PM10) is 150 μg∙m3 and PM2.5 is 65 μg∙m3 (3–5).5 The detectors were placed in a position where they should receive the greatest exposure. Data were simultaneously collected for one hour at each detector. The first set of samples was taken at a distance of about 3 m from the balloon explosion; 2 m from the demonstration point. Each detector was placed in the first-row, center seat of the lecture hall, where the person closest to the balloons besides the demonstrator could be found. Table 1. Flame Colors from the Metal Salts Metal Salt
Flame Color
LiCl
Red
SrCl2
Orange–red
CaCl2
Orange
Exploding Balloons
CuCl2
Green
Use a string and weights to anchor the balloon so that it floats halfway between the floor and ceiling at a safe distance
KCl
Purple (violet)
NaCl
Yellow
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 4 April 2008 • Journal of Chemical Education
519
In the Classroom Table 2. Detected Concentrations of Metal Solids in the Front of the Lecture Hall Sample Mass/ μg
Metal Iona
Li+ Ca2+ Cu2+ Sr2+ K+
1.5 ND
