why do onions make you cry science fair project

Does cutting an onion leave you in tears? The cells of an onion contain sulfur compounds. Cutting the onion causes a chemical reaction to occur, releasing an enzyme that reacts with the tear ducts. There are many techniques that are said to reduce tear production while cutting but which one is the most effective? Place 1 onion in the refrigerator. We will use this later in our experiment. Using a dulled kitchen knife dice the onion. Using a dulled knife will be the control. Subjectively describe your tear production and record. Wait an hour before proceeding. This will allow time for your eyes to recover. Using a sharpened kitchen knife dice the onion.

How does tear production compare to the control condition? Continue cutting the onion using the following methods, waiting an hour between each trial. a. Spray or coat the cutting board with vinegar and dice the onion. b. Take the onion out of the refrigerator and ensure the onion is chilled. Dice the onion. c. Put on a pair of airtight goggles such as swimming goggles. Dice the onion. d. Light a candle or turn on a gas burner. Dice the onion. e. Take a slice of white bread and bite on it so it hangs out of your mouth. Dice the onion. f. Cutting method: Cut the top of the onion (stem portion) off and slice towards the root but do not cut the root. g.

Fill your kitchen sink of a large basin with water approximately 6 in depth. Submerge your cutting board and onion and cut the onion under water. Terms/Concepts: Why do we tear up when cutting an onion? What happens to the onion chemically when we cut it? ; What are some techniques to prevent this reaction? ; What is the rationale behind each technique? How does it prevent tears? References:
A chemist would probably use a technique called gas or liquid chromatography to measure the amount of the odor causing compound. You might be able to compare different onion types by using a serial dilution technique to find the relative concentrations which smell the same to you. you could use samples of the same amount of onion of each of your comparison types.

You grind up each onion sample with the same amount of solvent(like water). Then take 1 drop of this sample and mix it with a few drops(like 9) of the same solvent(water). This is your first dilution. Take one drop of this and mix it with the same amount of water to make your second dilution sample. Keep doing this for several more dilutions. Do this for each of your onion samples.

Now designate one onion as your standard and find a dilution where you can just detect the odor. Then you can try to find the dilution of the other onion samples that smells the same to you. This way you can determine how strong one onion is relative to the others. I believe this technique is commonly used to test perfumes and food tastes. You need to be careful to rest your nose between trials as your sense of smell fatigues easily. You may also want to recruit several of your friends to help doing the comparison. Your results will be much more significant if several of you agree on the result. This could be fun!

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