science ace- thematic studies by: ng aik yang(20) 1a1
TRANSCRIPT
What is dry ice?
• Basically, dry ice is the solid form of carbon dioxide, which comprises of two oxygen atoms bonded to a single carbon atom.
Properties of dry ice• At temperatures above −56.4 °C , Carbon dioxide changes from a solid to
a gas with no intervening liquid form, through a process called sublimation.
• The opposite process is called deposition, where dry ice changes from the gas to solid phase.
• At atmospheric pressure, sublimation or deposition occurs at −78.5 °C .• The density of dry ice varies, but usually ranges between
about 1.4 and 1.6 g/cm3.
• The low temperature and direct sublimation to a gas makes dry ice an effective coolant, since it is colder than water or ice and leaves no residue as it changes state.
History of Dry ice
• The properties of solid carbon dioxide were discovered in the early twentieth century.
• It was first produced commercially in the 1920s in the United States.
• Until fairly recently, dry ice was often referred to as hot ice, a reference to the fact that when one touched the cold surface the hand felt burned.
How is dry ice produced?• First, gases containing a high concentration of carbon dioxide are
produced. • Such gases can be a byproduct of some other process, such as producing
ammonia from nitrogen and natural gas, or large-scale fermentation.• Second, carbon dioxide-rich gas is pressurized and refrigerated until it
changes into its liquid form. • Furthermore, the pressure is reduced. When this occurs some liquid
carbon dioxide vaporizes, and this causes a rapid lowering of temperature of the remaining liquid carbon dioxide.
• The extreme cold causes the liquid to solidify into a snow-like consistency.
• Finally, the snow-like solid carbon dioxide is compressed into either small pellets or larger blocks of dry ice.
Uses of dry ice
• Keeping food cold for a period of time• Some recent developments for its use include:
-using the pellets in blasting or cleaning-transporting medical specimens such as hearts, limbs and tissues for reattachment and trasplantation.
Fast facts about dry ice
• No significant chemicals are created in the production of dry ice.
• Dry ice can be used to loosen asphalt floor tiles or car sound deadening making it easy to pry off.
• Dry Ice Bombs! Check this out – Dry Ice Bomb
What is 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 with density at its boiling point of 0.807 g/mL and a dielectric constant of 1.4.
Properties of liquid nitrogen
• At atmospheric pressure, liquid nitrogen boils at 77 K (−196 °C; −321 °F) and is a cryogenic fluid which can cause rapid freezing on contact with living tissue, which may lead to frostbite.
• Liquid nitrogen freezes at 63 K (−210 °C; −346 °F).• 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.
Uses of liquid nitrogen
• store cells at low temperature for laboratory work• immersion freezing and transportation of food
products• coolant for overclocking a central processing unit, a
graphics processing unit, or another type of computer hardware
• freezing water pipes in order to work on them in situations where a valve is not available to block water flow to the work area.
• making ultra-smooth ice cream.
Liquid Nitrogen is FUN!
• Check these out:http://www.youtube.com/watch?v=DzNIJ7d3KR0
http://www.youtube.com/watch?v=MaxZwsqstFs&feature=related
Now, what happens if you mix dry ice and liquid nitrogen?
http://www.youtube.com/watch?v=ctPbhKldOgA
Bibliography
• http://www.madehow.com/Volume-7/Dry-Ice.html
• http://inventors.about.com/od/dstartinventions/a/dry_ice.htm
• http://en.wikipedia.org/wiki/Dry_ice• http://
www.britannica.com/EBchecked/topic/172281/Dry-Ice
• http://en.wikipedia.org/wiki/Liquid_nitrogen