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

Thursday, April 22, 2010

Hair rebonding

Hair rebonding soften, smoothen and straighten the hair. Most people wants their hair to be rebonded because they want they hair to look shiny and have a smooth like appearance. Keratin in our normal hair contains protein high in sulphur and amino acid cysteine. These chemical substances makes the keratin able to keep our normal hair strong and natural.
During rebonding, cream softener is used to break the hair structure. Then, a neutraliser is used next to straighten the hair again. The chemical use for hair rebonding affect the hair structure and its quality. The normal hair usually has keratin to keep the hair strong, however, when hair rebonding happens, the hair becomes weak tends to cause problems. Such example would be the loss of hair.
Hair rebonding is harmful. Although it gives you the appearance of hair a person would want, however, in reality, it only destroys and damage the hair structure and leads to more problems. If too much chemical is used during hair rebonding, it can damage the hair to the extend that the hair would become dry and or even hair loss.

Rachel - 3E2
Option 3: Onions.
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?

Onion is just like other plants. It is made up of cells which are separated by membrane into two parts. One part contains enzymes while the other part contains the molecules that consist of sulfur compound. When the onion is cute, some onion cells break open and the contents (enzymes and molecules that consist of sulfur compound) of membrane mix together. The enzyme causes the sulfur compound, amino acid sulfoxides to undergo a few chemical reactions. Sulfenic acids are formed, which are immediately coverted into a volatile gas, propanethiol S-oxide. The gas gets in contact with your eyes and reacts with the water present in the eyes. Certain chemical changes are taken place inside the eyes and a mild sulfuric acid is formed. This causes irritation of the eyes. Your eyes twinge while cutting the onion because the nerve endings in the eyes are very sensitive. The tear ducts in the eyes produce more water in order to dilute the irritating acid. However, this is good as the eyes are protected.

The irritation can be prevented by cutting the onions by different ways. One of the easy ways is to keep your head as far away from the onion as possible. Gas will mostly disperse before it reaches your eyes. Another simple way is to wear goggles. Another way is to peel the onion and chill t in the refrigerator before cutting, then it woud minimize a release of gas. This is because a change in the temperature alters the compounds present in the onion. You can also cut the onions under water or run the tap over the onions as you cut it.



When we cut onions, we break the cells releasing all their contents making amino acids sulfoxides form sulfenic acids. The enzymes that were separated are now able to mix with the sulfenic acids, thus producing propanethiol S-oxide. Propanethiol S-oxide is a volatile sulfur compound that noves upwards to our eyes. The gas reacts with the water in our eyes. Certain chemical changes take place in the eyes and there is the formation sulfuric acid. This sulfuric acid burns your eyes releasing tears to wash the irritating substance away. One way in which we can prevent the tearing of our eyes is by keeping it cool in a refrigerator before taking it out to cut it. this slows down the reactions and changes the chemistry in the onion. Another way of avoiding the tearing of the eyes is by cutting the onion under running water. Lastly, when cutting an onion, avoid the roots as it has a higher concentration of enzymes.

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.



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 problematic and more tears? Try chilling your onion before cutting it.

Done by adrian(23)3e2

Science(chemistry)-Networking Project

Q1.Why do onions make you cry?Q2.What is 'happening' in your eyes? Q3.What is/ are the chemical compound(s) that cause you to tear?Q4: How can you make onion-dicing less problematic?

A1:According to my research,Our eyes automatically start blinking and producing tears because of the irritants like chemicals such as sulfenic acids which produce a pungent odor which is converted by the LF-synthase enzyme into a gas called syn-propanethial-S-oxide, also known as the Lachrymatory which is also known as a crying factor

A2:Our eyes started to cry as it force / flush the chemicals that are received by our eyes out.

A3:As what i answer in question 1, it contains sulfenic acids, which is converted by the LF-synthase enzyme into a gas called syn-propanethial-S-oxide which is also known as Lachrymatory or crying factor.

A4: According to my research,there are lot of ways to make the onion-dicing less problematic. One way is to put them into the refrigerator to reduce the gas that it releases. Secondly, Cut fast!, and there more, like: put a slice of bread in your mouth, chew a gum while dicing and even dicing the onions with the help of running water.

Here is the link to the video which further improve our understanding about the question:

Done by: Ralph Joshua(34)
Class of 3e2

chemistry-hair rebonding

Hair Rebonding
Our hair is curly because of the sulphur bond of our hair. Rebonding simply break down the sulphur bond by heat and chemicals. During rebonding, keratin is added but it is only left on the surface of the hair instead of being the internal part of the hair naturally when it grew. Interferon alpha is a drug used to modify hair follicles and is used in rebonding but it only damages the hair texture. Neutralizers are used to stabilize the hair. A lot of money and time is needed to put in to maintain a rebonded hair. For example, it needs to be oiled, and it has to be redone whenever our hair grow to touch up any unneccessary curls.

Q3 Onion

It is because as we cut the onion, the onion itself contain oil. The gases release by the onion obtain sulfur which irrate our eyes and nose. When the gases Propanethiol S-oxide, is released and it rise upward encounter the water produced, the tear ducts is automatically blink, and produce tears which irriate the eye, and flush out the sulfuric acid in our eyelids, it produces sulfuric acid. In response to the sulfuric acid, our eye blinks and produce tears which irrate our eyes. Our tears contain the sulfuric acid. Thr chemical are Propnethiol S-oxide, sulfur , sulfuric acid and amino acid.
First we should put our onion in the cold water so the volative sulfured compound will react to the water. Then we froze the onion before cutting so the chemical reaction would be slow down.

Option 2 : hair rebonding

Rebonding is a chemical hair treatment that makes your hair straight, sleek and shiny. It is a permanent and expensive procedure. Prices for the treatment may vary across salons due to products used, service, your hair type and post treatment care. Each type of hair has a natural bond.Curly or wavy, are the result of natural bonds that give the hair its physical quality. The cream softener or relaxant used in the rebonding treatment breaks the hair structure. Then a neutraliser bonds the structure again and makes hair straight. In simpler terms the rebonding treatment changes your natural hair structure and restructures it. Once your hair is straightened you have to touch up the new growth every three months, six months or a year, depending upon your growth. Very strong chemicals are used to alter the structure of the hair, to break down its bonds (this is what gets rid of the curl) and to ‘rebond’ it again using chemicals to keep them straight. After shampooing, a cream softener or relaxant is applied to every hair shaft, keeping it thin plastic board. The hair is then steamed for 10 to 40 minutes, depending upon hair type and condition, and then rinsed. Hair is blow dried and then keratin lotion is applied and then it is ironed to further straighten it. Lastly a neutralizer is applied and kept for at least 30 minutes. After this procedure, one is not allowed to wash or tie back or even wet the hair for a few days. Even afterwards, you have to be extremely careful with your hair, since the rebonding process renders the hair shafts weak and very prone to breakage. You need to use a hair conditioner and hair serum regularly. It is also advisable to oil hair and to use a hair masque at regular intervals. If inferior products are used or you have the misfortune of going to an untrained professional, rebonding can go disastrously wrong and seriously damage hair, in extreme cases also sometimes results in hair fall and bald patches. So if you are considering hair rebonding, arm yourself with the knowledge of the possible pitfalls and the fact that you will have to take extra care afterwards. Any chemical process affects hair texture and quality. Excessive use of chemicals makes hair dry, weak and can even lead to hairfall. Hair rebonding requires post treatment care otherwise it may turn harmful. If you are suffering from hairfall, you must avoid rebonding or any other chemical hair treatment. Cheap chemicals, inexperienced hair stylists and weak hair can make rebonding a bad experience. Hair rebonding can turn into a disaster if you do not take care of your hair. Hair will need extra pampering once it has been rebonded. You cannot ignore your hair just because it looks straight and shiny. Rebonding done from a reputed and trustworthy salon lasts longer and hair quality does not suffer.

3) Onions

When we cut the onion, we cut through the cells, releasing their contents. Amino acid sulfoxides to form sulfenic acid. Enzymes that were kept seperated now are free to mix with sulfenic acid to form a volatile sulfur that reacts with your tears to form sulfuric acid, making your eyes "cry". The chemicals are amino acid, sulfenic acid, propanethiol sulfuric-oxide and sulfuric acid.
First, we can chop the onions in cold water so that the volative sulfured compound will react with the water but not our eyes. Second, we can freeze the onion for 10mins before cutting. It will slow down the chemical reaction of the volatile sulfured compounds.


Why do onions make us cry?
Like most other plants, onion is made of cells. These cells are separated by a membrane into two sections. One side of the membrane consists of enzymes, while other side contains the molecules that consist of sulphur compound. This is because when you cut the onion, a number of onion cells break open and the contents of both sides of membrane mix together and it would release a gas that will cause us to tear.This is because the onion contains oil, sulfur which will irritate both our eyes and nose.This causes a chemical interaction, a substance called prophanethiol s-oxide with the enzymes in the onion will emit a passive sulfur compound.

What happens in our eyes?
When this gas reach the water in our tear ducts in our eyelids, it would release a sulfuric acid.The nerve endings in the eyes are very sensitive and hence, your eyes twinge while cutting the onion.Our eyes would automatically blink and produce tears to flush out the sulfuric acid. This would also cause a burning sensation in our eyes. The brain would also send signals to the eyes to produce more tears.
What is/are the chemical compounds that cause us to tear?
The chemical compounds are synthase enzyme that converts the sulfoxides (amino acids) of the onion into sulfenic acid. The unstable sulfenic acid rearranges itself into a volatile gas, syn-ropanethial-S-oxide.

How can we make onion dicing less problematic?
As the onion has a pungent smell which will also irritate our eyes, we can try boiling it instead of directly slicing or dicing it first. We can also cut the onion under water as the water would wash away most of the sulfuric compound. Peeling the onion and storing it in the refrigerator before chopping may also help as the temperature change would be altered. Some people also tried biting a slice of lemon or bread may help to keep us from crying when cutting an onion. Wearing safety goggles may sound ridiculous but people wear it to prevent themselves from tearing too!

Option 1: Antiperspirant VS Deodorant

Definition and causes of body odor

Body odor is a perceived unpleasant smell our bodies can give off when bacteria that live on the skin break down sweat into acids - some say it is the smell of bacteria growing on the body, but it really is the result of bacteria breaking down protein into certain acids. the body. These bacteria multiply rapidly in the presence of sweat. Sweat is actually odorless; it is bacteria that live off perspiration on our body that create the bad smell.

Types of acid contain in the body odor .

Propionic acid and Isovaleric
acid is found in the sweat. These two types of acid are commonly present when there is body odor. Also , there are two types of sweat glands : Eccrine glands and Apocrine glands.Humans generate apocrine and eccrine sweat. Eccrine sweat is used to lower our temperature, like when we exercise or when it's really hot. It is produced uniformly all over the body and does not smell.

Apocrine is a special type of exudation that is produced in places like the armpits, groin, hands, and feet. It is the latter that causes all the trouble, but like eccrine sweat, it also doesn't smell. Apocrine perspiration simply contains fat and protein.

How does apocrine sweat tend to make us stinky?

Some bacteria on our body feed off apocrine sweat. Once they consume the sweat, they do what any living creature on earth does: they defecate . B.O. is the smell of bacteria excrement!

Actually, bacteria don't really defecate like we do -- they break down chemical bonds -- but they do consume our perspiration, and that makes us smell.

Causes of body odor also due to inadequate bathing (and/or cleaning/washing of clothes). It is caused by skin bacterial activity on sweat which has dried on the skin - and this makes people who sweat excessively more likely to be affected. In some people (the excitable 'greyhound/racehorse' types) the sympathetic aspect of the nervous system is dominant and they tend to sweat more, whereas in others (the calmer 'bulldog/carthorse' type) the parasympathetic aspect dominates and they tend to stay calmer. So keeping stress levels low is important for people who sweat a lot.

Antiperspirant vs Deodorant:
The variation most commonly used in deodorants and antiperspirants is Al2Cl(OH)5. Aluminium chlorohydrate is one of the most popular active ingredients in commercial Antiperspirants.

Types of Antiperspirant Deodorant

Deodorant kills bacterial through a number of ways. It may be a spray or aerosol product that contains alcohol that will temporarily kill bacteria. It might be a roll on or gel that contains an antimicrobial metallic compound. There are roll on deodorants made with naturally anti-microbial hops.It doesn't prevent you from sweating, but prevents bacteria from thriving on body parts where you sweat. A chemical called triclosan makes the underarm skin too acidic and that prevents your armpit from becoming a home to the bacteria, thus, reducing chances of bad odor.

spirant – uses various forms of aluminum to block the production of sweat. Aluminum reacts with compounds on the surface of your skin to form a kind of plug that blocks your pores.Antiperspirants differ from deodorants in that they don’t just mask the odor, but actually block the skin pores so that moisture isn’t released. The active ingredient that does this is an aluminum based compound that blocks the pores by forming a gel-like plug. Not only does this gel-like plug reduce odor, but it also keeps your underarms dry so you won’t stain your best white usually has a fragrance to make the user smell good. The association between exposure to aluminum and long term use of antiperspirants and Alzheimer's disease is a trend toward a higher risk with increasing frequency of use.

Deodorants or antiperspirants: Which is best?

While it may seem as if an antiperspirant would be the obvious choice since it has the dual function of reducing odor as well as keeping you drier, antiperspirants have been the subject of some health scrutiny. Aluminum compounds, like those found in antiperspirants, have demonstrated harmful effects in animals and are thought to be toxic to nerves and, possibly, to the kidneys.
However ,aluminum compounds used in the antiperspirants can get assimilated in the blood stream and cause serious health issues.

While deodorant can mask the odor temporarily, it cannot stop a person from sweating the way an antiperspirant does. Once the sweat combines with odor causing bacteria, the underarms will begin to smell again.


Deodorants and antiperspirants are used to stop the smell of body odor that is created by a combination of bacteria and sweat.Deodorants attack odor causing bacteria to eliminate smells whereas antiperspirants prevent your body from sweating and therefore keeps you both dry and smell-free.To compare which is the safer to use ,the answer will be Deodorants .Deodorants are considered to be safer than antiperspirants because they don’t stop the body’s natural method for cooling down.

Wednesday, April 21, 2010

CHEMISTRY - Option 1: Antiperspirant VS Deodorant


There are many causes which will leads to body odor. Some examples are – diet, gender, occupation, mood, health, medication and genetics.

Occupation and mood: wrecked promotion prospects at work, educational under – achievement because of teasing and bullying along with huge degrees of stress which is blamed for their frequent progression into alcoholism, immoderate tobacco or drug use in some cases to suicide.

Health: sometimes may be link with fixed health problems such as liver dysfunction, diabetes, digestive problems (parasites, etc) and yeast infections.

Diet: If the lively micro-organisms are unbalanced through use of medication (antibiotics and steroids in particular) or a high fat, high sugar, high red-meat, low fiber diet the lively role they play in detoxification of the bowel and in manufacturing important nutrients is impaired and this can exacerbate the condition of body odor, as well as to numerous other health problems.

Gender: In women, menstruation and stress often cause dramatically increases the degree of body odor experienced and careful attention to personal hygiene and dietary excellence is needed.


· Antiperspirants contain fragrance and contain a chemical compound that blocks the pores to stop the discharge of perspiration. There will be NO sweat, NO odor.

· Deodorant allows the release of perspiration, but prevents odor by combating it with antiseptic agents, which kill odor-causing bacteria.


Perspiration itself is almost unscented. Most of the odor that accompanies perspiration is caused by the action of bacteria. Deodorants reduce this odor in one of the three ways: by preventing the action of bacteria on the perspiration, by preventing the secretion of perspiration, or by masking the offensive odor with a pleasant one.

Deodorants that kill or inactivate bacteria contain antiseptic substances, such as alcohol, formaldehyde, and boric acid. Chlorine compounds, e.g. hypochlorite and chlorhexidine, work by killing bacteria which may be responsible for the odor. Deodorants that mask perspiration odor contain perfumes. Essential oils and such disinfectants as carbolic acid simply mask the odor, making it less offensive.


Deodorants that prevent the secretion of perspiration are called antiperspirants. They usually contain an aluminum salt, such as aluminum sulfate, that acts by blocking the pores preventing the free flow of sweat.

Aluminum-based antiperspirants work by blocking the sweat ducts, thereby reducing the amount of sweat that reaches the skin’s surface. Aluminum salts are soluble as long as the formulation is acidic (low pH). When they are applied to skin and come in contact with sweat, the pH rises causing the aluminum salts to precipitate out and form a plug over the sweat glands. Sweat continues to be produced by the sweat gland but it just isn't able to reach the surface of the skin.

Diphemanil methyl sulfate is a drug that opposes the action of the parasympathetic nerves that control sweat production.


Healthcare professionals recommend deodorant over antiperspirant as they believe that obstructing pores and preventing perspiration may not be the healthiest choice.

Aluminum compounds or aluminum salts, such as aluminum oxide (Al2O3), are key ingredients in almost every antiperspirant. They are powerful astringents that close pores, stopping sweat and odor from escaping the body.

The active ingredient of the product consists of any of the following within the established concentration and dosage formulation. Where applicable, the ingredient must meet the aluminum to chloride, aluminum to zirconium, and aluminum plus zirconium to chloride atomic ratios described in the U.S. Pharmacopeia-National Formulary. The concentration of ingredients in paragraphs (b) through (j) of this section is calculated on an anhydrous basis, omitting from the calculation any buffer component present in the compound, in an aerosol or no aerosol dosage form. The concentration of ingredients in paragraphs (k) through (r) of this section is calculated on an anhydrous basis, omitting from the calculation any buffer component present in the compound, in a no aerosol dosage form. The labeled declaration of the percentage of the active ingredient should exclude any water, buffer components, or propellant. Sweating is nature’s way of lowering the temperature of body and prohibiting this by blocking the pores is not ideal. Also, the aluminum compounds in the antiperspirants are not healthy friendly stuffs. Antiperspirant increases danger of breast cancer, especially if it’s applied their underarms.

Deodorants contain parabens which believe to cause breast cancer.



Onions by [Nicholas Khng]

Why do onions make you cry?

It is not the odor from the onion that makes us cry, but the gas that the onion releases when cut. It is an irritant to both our noses and to our eyes. Cutting an onion arouses a gas contained within the onion. When this upwardly mobile gas encounters the water produced by the tear ducts in our eyelids, it produces sulfuric acid. In response to the caustic acid, our eyes automatically blink, and produce tears which irrigate the eye, and which flush out the sulfuric acid. We will tear up.

What is 'happening' in your eyes?

When the volatile gas, syn-propanethiol S-oxide react with water present in our eyes, chemical changes inside our eyes take place and a mild sulphuric acid formed in our eyes. It irritate and make our eyes pain, the nerves in the eye detected and stimulate tear duct to produce more water to dilute the acid out to the eyes, so that our eyes are protected.

What is/ are the chemical compound(s) that cause you to tear?

Onion cells are separated by a membrane into two sections, one section contains enzyme, and the other one section contains amino acid sulfoxides which form sulfenic acid when reacting with enzyme, and it is so unstable. When cut, some cells in the onion breaks, this resulted in the combination of the two chemical, the enzyme and sulfenic acid. The enzyme causes unstable sulfenic acid undergo some chemical reactions, and it turned into syn-propanethiol S-oxide immediately.

How can you make onion-dicing less problematic?

There are 4 ways. 1) Heat the onions before you cut them. This destroys the allinase which causes the reaction to happen in the first place, so the onion cannot make you cry. 2) Cut the onions outside in a well-ventilated area 3) cut them under water. 4) Chill the onions before cutting


Adult tearing
Different variety of onions
An onion

According to history, scientist used to put the blame on enzyme allinase for the cause of tearing when we slice onion. however proved by the studies on in Japan, Lachrymatory-factor synthase also known as syn-propanethial-S-oxide are the one who caused the tearing. when onion is being sliced, its cells would realease allinase enxymes and amino acid sulfoxides. It is converted by the LF-synthase enxymes into Lachrymatory factor(Syn-propanelthial-S-oxide), and those acids would rearrange themselves into thiosulfinates. Soon the Lachrymatory factor(Syn-propanelthial-S-oxide) gets into the air and contact with out eyes. The first part of the eye which is also known as cornea, is populated by autonomic motor fibers that lead to the lachrymal glands. When Lachrymatory factor(Syn-propanelthial-S-oxide) is being dected, the fibers found in cornear would start to produce tears to wash away the irritants. this happen by nature, as a protection towards harmful gaseous.

Diced/sliced onion

A special kind of goggle used to prevent tearing when your are dicing onion

we would easily prevent ourselves from tearing with the below methods.
Method One : Have your onion refrigerated before cutting as it would help to slow down reactions and changes chemistry inside the onion itself.
Method Two: Cut the rot of the onion as it contains the gland that tear us up
Method Three: Having a sharp knife-- A dull knife crushes the onion instead of cutting it, therefore allowing more acids to be in the air. Sharp knife on the other hand also help to slows down reactions.
Method Four: Burn a candle on the counter when you are cutting your onion. this would be helpful as it would burn off fumes that cause your eye to tears.
Method Five: Placing a piece of bread on the knife top would help to absorb the fumes that cause your eyes to tears.



Why do onions make us cry?
This is because the onions contains gas that it releases when we sever this member of the lily family. When the passive sulfur compound encounters the water produced by the tear ducts in our eyelids,it produces sulfuric acid. Thus,when the gas response to our eyes,our eyes will automatically blink and tears will be rolling down our cheeks.

What is happening in our eyes?
The sulfuric acid that irritates our eyes,causing a stinging sensation. The brain signals our tear ducts to produce more tears to help protect the eye.

What is the chemical compounds that cause you to tear?
Onion contains an acrid that stimulates the tear glands and the mucous membranes of the upper respiratory tract.
Onions are low in sodium and contain no fat.
Onions are also a source of vitaminC,potassium and dietary fiber.
The strong smell of the onions contains allins which is also called amino acid.

How can you make onion-dicing less problematic?
We should not rub our eyes after we cut the onions. It is the worst thing that we can do. This is because more onion juice will be absorbed in your eyes. A good way to reduce possible eye irritation is to cut the onion underwater. The water will dissolve most of the sulfuric compound.


Q3) When you cut an onion, it releases a gas called, ready for this, Propanethiol S-oxide. When mixed with certain enzymes in the onion, it creates a sulfur gas. These gases then get to your eyes and create a mild acid which irritates the 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. Normally, your body would signal you to close your eyes. This, of course, is not a good idea if you are cutting an onion. The next best thing your eyes can do is to make tears to protect the eyes. Rubbing your eyes is a bad idea, since your hands are likely full of the tear making onion juice. Wearing safety goggles, however, should reduce the tears every time.

Chemisty (Onions)

When you are cutting an onion,the cell is broken and the contents is released. Amino acid sulfoxides form sulfenic acids.Enzymes mixed with the acids and produce a compound called volatile sulfur.
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 were ract with the tears in your eyes to form sulfuric acid.
The sulfuric acid burns, stimulating your eyes to release more tears to wash the irritant away.
A gas called syn-propanethial-S-oxide which is also known as Lachrymatory Factor. They exist for a very short time before converting themselves into thiosulfinates.

Prevent it by:
1.Use a sharp knife. A sharp knife will cause less damage to cell walls, and fewer irritants will be released.

2. Chill the onions. When you cut the onion, you rupture the onions cells, this causes enzymes to interact with sulphoxides and produce the gas that causes your eyes to sting. When you chill the onion, the enzymes produce significantly less gas, hence less crying.
3. Run the vent hood. Position your cutting board next to the stove and turn on the exhaust fan. Irritants will be pulled away from you and your eyes.
4.Put a little bit of vinegar on the chopping board to prevent from tearing.


Tuesday, April 20, 2010


When you cut an onion, you experience a tearing and burning sensation. It is not the strong odor of the onion that makes us cry, but the gas that the onion releases when you cut it. When you cut onions, you break the cells thus releasing the Amino acid sulfoxides which form sulfenic acids. These sulfoxides are the main source of tearing. When you chop onions, it releases a mist of synpropanetheal s.oxide which is a volatile compound. The strong smell of onions come from the oil they contain. This oil evaporates easily when the onion is peeled or cut. The vapour from the oil affects the nerves in your nose which are connected to your eyes and make them water. The moisture in your eyes react with the gas that creates a very mild sulphuric acid. Your eyes then form tears as a natural defence that dilutes the acid to flush it out.

Ways to prevent tearing of eyes are as followed: Wearing of safety googles, refrigerate your onions before cutting (it slows the reaction), by cutting your onion under water, or you can put a fan beside to blow away the gasses released from the onions. Do not rub your eyes because, the onion oil on our hands enters our eyes, thus making it worse.

Here is the link to the video which will further improve our understanding about the question:

Sean james-35-3e2