In every part of our daily lives, chemistry is involved whether we notice it or not. Thus, we will be zooming in on an aspect which we experience daily, or probably for most of the time, that is, the kitchen. Here are a few examples regarding chemistry in the kitchen.
The Tear-jerking Vegetable
Onions – the vegetable that causes inevitable tears when you slice them open. We all know they makes our tears fall, but we never really know why. What is it that makes our eyes burn? Well, you can put the blame on chemistry.
When an onion is cut, it’s cell structure breaks, allowing it’s contents, including amino acids sulfoxide, to be released. This produces a compound called sulfenic acid. The sulfenic acid reacts with the enzyme lachrymatory-factor synthase forming syn-propanethial S-oxide (C₃H₆OS). This chemical rises and reacts with the tears that are already present in the eye forming sulfuric acid – the acid used for batteries! This triggers the tearing and stinging sensation.
There are 3 types of tears:
- Emotional tears – when we are sad
- Basal tears – keeps our eyes lubricated, thus constantly replenished
- Reflexive tears – to wash away irritants
The eyes are equipped with sensory nerves that protects the eye from physical and chemical irritants. It sends the signal to the central nerve system that can feel the burning sensation. Then the signal is carried to the lacrimal glands that releases the tears to wash the irritant away.
Here are some advice/ tips to cutting onions:
- Wear goggles
- Use a ventilator or fan to blow the chemical away
- Use a sharp knife to prevent a worser damage to the cell structure
- Refrigerate before cutting to reduce the tendency of the onions releasing volatile compounds that turn to gas
Rust On Pan (Rust + Coke)
If you procrastinate at every aspect of life, chances are, you have left your skillet in the sink after cooking. That is if you even cook. The worst part is not bearing to scrub the skillet with a brillo pad for like, an eternity. Fortunately, there is a way to make your job easier – with the use of Coke.
Coke consist of a chemical called phosphoric acid that contributes to the sour taste in the super sweet soft drink. Phosphoric acid (or hydrochloric acid – an alternative) is commonly used to remove rust and tarnish from metal as it dissolves rust a much faster speed than it dissolves iron. Phosphoric acid has a pH value of 2.8. It can dissolve a nail in 4 days! The acid reacts with the ferric oxide (rust) to form ferric phosphate and water. The chemical equation can be seen in the following:
The hard-to-clean iron oxide turns into blackish ferric phosphate (or iron phosphate) that can be scrubbed right off though it leaves iron phosphate as a coating on the metal surface due to chemical reaction effects. The water will be washed off during cleaning process. The effects of the acid on the metal surface will not be of significance unless exposed for a long period of time or at high concentrations.
The Egg That Went Bad
Can’t tell if your eggs are bad? You might want to call chemistry for a little help. Use the following steps:
- Get a glass/ cup of tap water.
- Place the egg inside.
- Floats = Bad , Sink = Good
Now you might wonder, why so? The egg shell consists of about 7000 tiny pores. Logically speaking, over time, more gas will enter the egg. This causes the air cells to become larger thus the buoyancy of the egg.
more gas = more floating
Make sense? This, however, is partially correct. The real reason to why it floats is not not really due to air entering, rather the mass leaving the egg. The density solely depends on the mass because the egg shell does not contract or expand. If it weighs more, it sinks. Weighs less and it will float. Hence, we can say that density of a good egg is higher than that of tap water, which enables it to sink.
Density = Mass / Volume
As the egg decomposes, water vapour and other gases leaves the egg through the porous shell and surrounding air will enter though the overall mass is reduced as the yolk and whites shrink, making the air cell larger.
more mass leaving = lesser density = floating
The Soap Opera
Have you heard of the heartbreaking love story between oil and water? One day, they broke up because oil was clearly cheating on water. It wouldn’t leave plate. Was it love? Water wanted to fight for oil’s love back but failed because they have opposing properties that didn’t complement each other. DDDUUNNN DDUUNNN DUNNN. It is impossible for water, all by itself, to make oil leave plate. Soap couldn’t stand all that drama, and decided to step in to end water’s misery. Soap did it, but how? Let’s find out.
Oil is made up of long, non-polar (cannot dissolve in water) hydrocarbon molecules whereas water is made up of short, polar (can dissolve in water) molecules. Hence, they don’t mix. Everyone can agree on this by doing a simple experiment by mixing oil and water. It is simply impossible. 2 layers would be visible – oil on top and water below as oil has a lower density than water. Soap, or detergent, acts as an emulsifying agent. Emulsifying agent are soluble in both fat (in this case, the oil) and water. It possesses both hydrophilic and hydrophobic side, which enables it to interact with oil and water.
hydro = water; philic = loving; phobic = fearing
From this we know that oil is readily mixed with hydrophobic molecules, and water is readily mixed with hydrophilic molecules.
The following context can be related to when we wash our dishes:
When oil is mixed with soapy water, the molecules in the soap will arrange themselves into tiny clusters called micelles (refer to picture below). The hydrophilic part of the soap molecules will form the outer surface of the micelle by sticking to the water. Similarly, the hydrophobic part of soap molecules traps the oil in the center as it unable to be in contact with water. The micelle will then be soluble in the mixture. As the soapy water is rinsed, the oil is washed away too.
Going back to the story, I guess you can say soap did a great job.
Bonus information, not relating to kitchen.
Don’t you just love how light sticks glow brilliantly in the dark? Light sticks come in various colors. The color of the light is determined by the chemical make-up of the fluorescent dye in the stick. Light sticks use energy from a chemical reaction to emit light. This chemical reaction is set off by mixing multiple chemical compounds.
When you combine 2 or more compounds, the various atoms may rearrange themselves to form compounds. Depending on the nature of the compounds, this reaction will cause either a release or an absorption of energy. The reaction between the different compounds in a light stick causes a substantial release of energy. The atoms in the materials are excited, causing electrons to rise to a higher energy level and then return to their normal levels. When the electrons return to their normal levels, they release energy as light. This process is called chemiluminescence.
A typical light stick holds a hydrogen peroxide solution and a solution containing a phenyl oxalate ester and a fluorescent dye. Here’s the sequence of events when the two solutions are combined:
- When you bend the plastic stick, the glass vial snaps open, and the two solutions flow together. The chemicals immediately react to one another, and the atoms begin emitting light.
- The hydrogen peroxide oxidizes the phenyl oxalate ester, resulting in a chemical called phenol and an unstable peroxyacid ester.
- The unstable peroxyacid ester decomposes, resulting in additional phenol and a cyclic peroxy compound.
- The cyclic peroxy compound decomposes to carbon dioxide.
- This decomposition releases energy to the dye.
The electrons in the dye atoms jump to a higher level, then fall back down, releasing energy in the form of light.
Although the light-producing reaction is not caused by heat and may not produce heat, the rate at which it occurs is affected by temperature.
Hence, if you place a light stick in a cold environment (e.g. freezer), the chemical reaction will slow down. Less light will be released while the light stick is cold, but the stick will last much longer.
If you immerse a light stick in hot water, however, the chemical reaction will speed up. The stick will glow much more brightly, but will wear out faster too.
As you can see from presented points, chemistry is always behind the things that happen in the kitchen. Help yourself by trying out the different experiments or heeding advice given earlier on in your kitchen. We hope you have took away some good pointers. Thank you for reading.
Rust on pan: