Science Ace- Thematic StudiesBy: Ng Aik Yang(20) 1A1

Dry Ice

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.

How is dry ice produced?

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

Liquid Nitrogen

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

THE END

Can someone turn on the heat?