group 2 - eye watering chemistry and fruits browning

Group member: Bryan David Kai En, Henry Chua Hanlong, Lim Zong Da, Murali Kumanan, Qi Tianjiao Descriptions and concepts of the chemistry phenomena of daily life in the Kitchen: 1.When we cut onions (usually are our parents), our eyes usually feel uncomfortable and after a while we cry. Reason: The gas, propanethial-S-oxide that onion releases when cut is the reason of tearing. Propanethial S-oxide is a lachrymator, an irritant that causes the eyes to fill with tears without damaging them. When a lachrymator comes into contact with the surface of the eye, the cornea, it is detected by the nervous system and triggers a response from the lachrymal (tear) glands. Tears are then produced in order to dilute the irritant. Propanethial S-oxide is relatively volatile and when its vapours come into contact with the eye a small amount reacts to form sulfuric acid, causing the burning and itching sensations that accompany the tears. The forces between syn-Propanethial S-oxide molecules are weak induced dipole-induced dipole attractions since the O=S bond is polar and the molecule is asymmetrical. The weak dispersion force is also due to its small molecular size. Compared with the amino acid sulfoxide, syn-Propanethial S-oxide is a much smaller molecule. Thus the intermolecular force is weaker than that between amino acid sulfoxide. This is the reason why syn-Propanethial S-oxide exists in the gaseous state under room temperature. 2.When we prepare fruit salad, for example apple and banana, we will find that after we cut the fruits, their colour will change to brown and will not look fresh anymore. Reason: An oxidation reaction takes place here. When fruits or vegetable are peeled or cut, enzymes in the plant tissue are exposed to the air. The enzyme polyphenol oxidase (phenolase), in contact with oxygen, catalyzes one step of the biochemical conversion of plat phenolic compounds to brown pigments known as melanins. This reaction is known as enzymatic browning and occurs at warm temperatures when the pH of the plant material is between 5.0 and 7.0. This reaction is also speeded up by the presence of iron ( such as an iron or rusted knife) or copper (such as a copper bowl). In the video, we also talked methods to prevent the browning of fruits and tearing. Explanation for the reasoning of the methods also included in the video.