Discover Chemistry

When you slice an apple or peel a banana, it doesn’t take long before the bright, fresh surface begins to turn brown. This change is not due to spoilage but a natural chemical process known as enzymatic browning .  Understanding the science behind this reaction reveals how chemistry operates in the most ordinary foods we eat daily. 1. The Role of Enzymes in Browning Inside the cells of fruits like apples, bananas, and pears exists an enzyme called polyphenol oxidase (PPO), sometimes referred to as tyrosinase . Under normal conditions, this enzyme is kept separate from oxygen and certain compounds known as phenolics .  When the fruit is cut, peeled, or bruised, the cell walls break down, allowing PPO to come into contact with both the phenolics and oxygen from the air. This interaction triggers a chain of chemical reactions that transform colorless compounds into brown pigments on the fruit’s surface. 2. The Chemistry of Oxidation At the heart of this process lies a simple ox...

Milk is one of the most common household items, but it also spoils quickly if not stored properly. You may have noticed that when milk is left outside the refrigerator for a few hours, it develops a sour taste and an unpleasant smell. This simple observation hides fascinating chemistry and microbiology. Let’s explore why milk turns sour when left outside and how temperature, bacteria, and chemical reactions play key roles in this process. 1. The Composition of Milk – A Perfect Growth Medium Milk is a nutrient-rich liquid containing proteins, fats, carbohydrates, vitamins, and minerals. The main sugar in milk is lactose , a disaccharide made of glucose and galactose. While this makes milk highly nutritious for humans, it also provides an ideal food source for microorganisms, especially bacteria. When milk is stored at room temperature, these bacteria begin to multiply rapidly, leading to spoilage. 2. The Role of Lactic Acid Bacteria Even fresh milk contains a small number of lactic a...

Picture this: a glass of cold water with ice cubes bobbing on top. It feels normal, almost boring — but scientifically, it’s one of the strangest quirks in all of chemistry . Most solids sink in their liquid form . Iron sinks in molten iron.  Solid wax sinks in melted wax. So why does solid water — ice — float instead of sinking? The answer lies in a beautiful chemical exception that makes life on Earth possible. The Usual Rule of Chemistry Normally, when a substance freezes, its molecules get packed closer together, making the solid denser than the liquid. That’s why solids usually sink. Density, after all, is just mass per unit volume. If the same amount of material occupies less space, it becomes heavier per unit of volume and sinks. But water breaks this rule. When it freezes, it actually expands, becoming less dense than liquid water. That’s why ice floats, defying the expectation we’d set from almost every other substance. The Hydrogen Bond Trick The secret is in water’s mol...

Almost everyone has faced this: you’re peacefully preparing dinner, knife in hand, when suddenly your eyes start to sting and tears roll down your cheeks. It feels almost personal — as if the onion is fighting back. But the truth is far stranger, and much more fascinating: it’s chemistry at work. The Onion’s Defense System Onions don’t “want” to be eaten. Like many plants, they’ve evolved clever chemical defenses. When you slice into an onion, you’re not just cutting through layers of cells — you’re breaking tiny storage sacs filled with special compounds. This is the onion’s natural alarm system, designed to deter animals (and maybe even you) from munching on it too quickly. Meet the Tear Gas Molecule The real culprit is a molecule with a dramatic name: syn-Propanethial-S-oxide. Here’s how it forms. Inside the onion, a harmless substance called sulfoxide sits quietly in the cells. When you chop the onion, an enzyme called alliinase is released. This enzyme reacts with the sulfoxides, ...

Oxygen is one of Earth's most abundant and crucial elements, with profound impacts on chemistry, biology, and the environment. This article delves into various aspects of oxygen, from its discovery and properties to its role in human health and the environment. Discovery and History Oxygen was discovered independently by Carl Wilhelm Scheele in Sweden and Joseph Priestley in England, both in 1774. Priestley isolated oxygen by heating mercuric oxide, while Scheele produced it by heating several compounds, including potassium nitrate. Antoine Lavoisier, a French chemist, later named the element "oxygen" in 1777, from the Greek words "oxys" (acid) and "genes" (producer). 1. Triplet Oxygen    - Molecular oxygen (O2) is commonly depicted with a double bond, but in reality, it has two unpaired electrons, making it a diradical. This makes it slightly paramagnetic, meaning it is weakly attracted to magnetic fields. 2. Oxygen's Discovery    - Oxygen was dis...