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!

Mrs. Yeoh

Wednesday, May 5, 2010

Why Do Onions Make Us Cry???

Why do onions make us cry?
Most of us think that the reason why our eyes sting when we cut onions is due to the very strong odour of the onion. However, this is not really true. What is the answer then? Well, our eyes cry because of the gas that the onion releases when we severe it, propanethiol S-oxide.
The onion itself contains oil, which contains sulfur, which likes to irritate both our noses and eyes. Cutting an onion arouses propanethiol S-oxide, whi
ch then couples with the enzymes in the onion to emit a passive sulfur compound. When this upwardly mobile gas encounters the water produced by the tear ducts in our eyelids, it produces sulfuric acid. In response to the acid, our eyes automatically blink, and produce tears which irrigate the eye, and which flush out the sulfuric acid.
Another reflex to rid the eyes of a foreign substance, that of rubbing our eyes with our hands, often exacerbates the situation, because our hands are coated with the caustic, sulfuric acid producing oil from cutting the onion, which we then rub directly into our eyes.

How do we avoid crying when cutting onions?
The only remedy for ridding the onion of its pungent and irritating oil is to boil it.
Another way is to wear protective glasses so that not much of the gas may enter the eyes.
Also, we can usually wash our eyes, even though it may cause to be a nuisance.

Done by: Siti Farina

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