Important annoucement - Chemistry

Dear 3E2,

See you guys for extra lesson on 5 May (Wed) 2.30pm.

Jia you in your exam preparation!

Eat well and sleep well too!

Cheers,
Mrs. Yeoh

Thursday, April 22, 2010

Chemistry(onions)

Question:

Why do onions make you cry? What is 'happening' in your eyes? What is/ are the chemical compound(s) that cause you to tear? How can you make onion-dicing less problematic?

when you cut an onion, you break cells, releasing their contents. Amino acid sulfoxides form sulfenic acids. Enzymes that were kept separate now are free to mix with the sulfenic acids to produce propanethiol S-oxide, a volatile sulfur compound that wafts upward toward your eyes. This gas reacts with the water in your tears to form sulfuric acid. The sulfuric acid burns, stimulating your eyes to release more tears to wash the irritant away

Here are ways to make onion-dicing less problematic. Keeping the onion wet, or cutting under water is very effective, as the gas immediately reacts with the water around the onion and never reaches the eyes.Glasses and goggles also prevent the gas to penetrate the eyes to some degree, goggles being the most effective (although not practical).Cooling the onion may also help, as the enzyme activity is much slower at low temperatures.Here are some videos url which show how onion dicing can be less problematichttp://www.youtube.com/watch?v=lnTysxxIomU andhttp://www.youtube.com/watch?v=QxzO71UvPEANo more tears? Try chilling your onion before cutting it.

Done by adrian(23)3e2

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