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

Science Chemistry Networking Project - Onion [Vincent]

Question:Why Do Onions makes us cry?What is happening in our eyes?What is/are the chemical compound(s) that cause you to tear?How Can you make onion-dicing less problematic?

Actually when onion make us cry , it is not the strong odor that makes us to cry but the gas that releases from the onion when we cut it.

The onion itself already contain oil in it which contain sulfur which irritant our eye and nose.
When we cut the onion, it will actually produce a gas called Propanethiol S-Oxide.

This gas which will combine with the enzymes contains inside the onion and emit a passive sulfur compound. The passive sulfur will then travel upwards to your eye and when it encountered the water in our eyelid produced by our tear ducts , it will then produce sulfuric acid.

These caustic acid makes our eye blink automatically, to protect from these caustic acid , your brain will tells your eye duct to produce more water so that it will dilute the irritating acid and the sulfuric acid will be flush out.

We can make onion-dicing be less problematic.There are actually 2 ways you can do it, the first way is that you chop the onion under cold water so that when the passive sulfur compound is produced out , it will react with the cold water first instead of reaching your eye.

Another way is that before you cut the onion, you freeze the onion for 10 minutes. By doing this, it will coolder the temperature of the onion and it will slow down the chemical reaction which form the passive sulfuric compound.This will also slows down all the activities of the enzymes.

By Vincent.

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