Wednesday, April 28, 2010

Liquid Nitrogen Facts

Being a Chemistry teacher, we get to experience different experiments, those conventional titration ones and even the more dangerous one like using liquid nitrogen.

In this post, I'm going to share with you videos which I took at a distance, during one of my laboratory lessons in NIE. It's one of those practical work lessons whereby only the professor can demonstrate but student-teachers can only watch and experience.

First and foremost....I will definitely give you a background on what is liquid nitrogen...

Facts about Liquid Nitrogen

Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid. 

At atmospheric pressure, liquid nitrogen boils at 77 K (−196 °C) and is a cryogenic fluid which can cause rapid freezing on contact with living tissue, which may lead to frostbite. When appropriately insulated from ambient heat, liquid nitrogen can be stored and transported, for example in vacuum flasks. Here, the very low temperature is held constant at 77 K by slow boiling of the liquid, resulting in the evolution of nitrogen gas. Depending on the size and design, the holding time of vacuum flasks ranges from a few hours to a few weeks.

Liquid nitrogen can easily be converted to the solid by placing it in a vacuum chamber pumped by a rotary vacuum pump. Liquid nitrogen freezes at 63 K (−210 °C;). Despite its reputation, liquid nitrogen's efficiency as a coolant is limited by the fact that it boils immediately on contact with a warmer object, enveloping the object in insulating nitrogen gas. This effect, known as the Leidenfrost effect, applies to any liquid in contact with an object significantly hotter than its boiling point. More rapid cooling may be obtained by plunging an object into a slush of liquid and solid nitrogen than into liquid nitrogen alone.
So why is it sooo dangerous??

Because of its extremely low temperature, careless handling of liquid nitrogen may result in cold burns.

As liquid nitrogen evaporates it will reduce the oxygen concentration in the air and might act as an asphyxiant, especially in confined spaces. Nitrogen is odourless, colourless and tasteless, and may produce asphyxia without any sensation or prior warning. A laboratory assistant died in Scotland in 1999, apparently from asphyxiation, after liquid nitrogen spilled in a basement storage room.

Vessels containing liquid nitrogen can condense oxygen from air. The liquid in such a vessel becomes increasingly enriched in oxygen (boiling point = 90 K) as the nitrogen evaporates, and can cause violent oxidation of organic material.
Here are the videos!! (P.S. It may not be so clear because of where I'm seated but it serves it's purpose - to convey the danger of liquid nitrogen!!)

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