Cross-disciplinary group of students and faculty explore basic chemistry principle as they make ice cream with liquid nitrogen
I scream, you scream, we all scream for … a chemistry experiment?
Yes. Chemistry and biochemistry lecturer and chemistry laboratory coordinator Marie Agan created a sweet start to the fall semester by creating liquid nitrogen ice cream. The exercise, presented by Norwich University’s American Chemical Society chapter, drew students and faculty from across disciplines and across campus on Aug. 26, when the outdoor temperature topped 90 degrees Fahrenheit.
Some kitchen scientists might have made ice cream with bags, combining heavy cream, vanilla extract and sugar (or other flavor) in a large resealable bag, combining ice and rock salt in a smaller resealable bag, then putting the smaller bag in the bigger one and shaking vigorously. As Scientific American reports, this works because the rock salt lowers the cream’s freezing point, creating a freezing-point depression.
Liquid nitrogen is typically made from air, which is about 78% nitrogen. At room temperature, nitrogen is a gas, but at very low temperatures, nitrogen changes phases, going from gas to liquid.
Agan’s experiment used liquid nitrogen, which is nitrogen gas at extremely low temperature, to provide the cold. (Liquid nitrogen’s boiling point is -312 degrees Fahrenheit.) Students poured the liquid nitrogen over a base of heavy cream, corn syrup and vanilla extract and stirred with a big wooden paddle.
Liquid nitrogen is typically made from air, which is about 78% nitrogen. At room temperature, nitrogen is a gas, but at very low temperatures, nitrogen changes phases, going from gas to liquid.
As Discover magazine reports, pouring liquid nitrogen over an ice cream base like the one Norwich’s students made reduces the base’s temperature quickly. The mixture’s molecules move less and water molecules form small seed crystals, Discover reports; and stirring the mixture (adding mechanical energy) breaks the crystals into tiny pieces to create a smoother-than-supermarket-varieties ice cream. (The ice cream shop chain Creamistry, which operates in six states in the southern and western United States, creates its products using liquid nitrogen.)
Fun and friendly
Agan, who joined Norwich’s faculty in 2018 and advises Norwich’s American Chemical Society chapter, said the experiment demonstrated a basic scientific idea — the nitrogen’s phase change. And, she said, it was fun. Students, who wore safety goggles, oven mitts and protective laboratory coats, took turns stirring the mixture in the 15-gallon pot and watching the ice cream’s creation.
Agan said the ice cream experiment introduced students to the American Chemical Society, which was founded in 1876, chartered by Congress, and includes 155,000 members in 150 countries. On its website, the group said it aims to improve people’s lives through chemistry’s transforming power.
She said the exercise also drew students and faculty from across campus. The faculty group included Dr. Sarah Gallant and Emma Ste. Marie, both assistant professors of chemistry and Chemistry and Biochemistry Department Chairman and associate professor of chemistry and biochemistry Dr. Ethan Guth.
Meanwhile, engineering and physics students mixed with chemistry students. (Agan was also involved in the 2020-21 academic year’s cross-disciplinary Wastewater-Based Epidemiology Initiative, which combined engineering, chemistry and communications students to collaborate on an early detection system for COVID-19.)
“It got to be this really nice mix of students who will see each other in class,
Agan said of the ice cream making. “It was a way to use a fun bonding experience as a scientific lesson.”
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