Trivia

奈米科技在近年來成為科技業的寵兒，無論是怎樣的科技產物只要掛上奈米兩個字似乎就成為了工業界的熱門商品。但真正的奈米又是指什麼呢？基本上，在長度單位下，國際所通用的公共單位是公尺(meter)，簡稱為米(m)，而奈米便是指，其比例是10^-9 m的長度，標記為奈米(nm)，而在這樣極短的長度下，許多化學物質會呈現出與巨觀下完全不同的化學性質，因此稱為奈米科技。一般所用的奈米材料是指有單一個方向的長度是100 nm以下的特殊化學物質，奈米金就是其中一種。

而奈米金在生活中究竟有哪些用途呢？由於當物質在長度變得極度微小的時候，在光線通過時與日常生活巨觀下所吸收的光線波長並不相同，也因此容易產生落入可見光區(紅橙黃綠藍靛紫色光)的互補色，使我們得以看見不同的色彩。就如同我們在日常生活中所看見的黃金是閃亮耀眼的金黃色，但在奈米等級的大小時，黃金顆粒的色彩可以是紫色深紅色甚至是黑色。根據這種色彩的特性，人們在很早以前，便懂得拿奈米金當作紅寶石色玻璃或陶瓷的原料，最有名的例子便是西元前 4 ~ 5 世紀的羅馬酒杯。正常的狀況下我們看到的酒杯是綠色，但如果光是從酒杯內照出酒杯外時，穿透光卻是紅寶石色。

而也因為尺寸大小直接的影響了奈米金粒子的色彩改變，因此科學家便想盡一切辦法，讓奈米金在醫學上可以派得上用場。透過奈米金在人體內不同的器官與組織可能會因為環境的改變而凝聚或是分散產生不同的顆粒大小，並且產生色彩的變化，就能夠針對人體的健康狀況做出檢驗。目前有一部分的驗孕劑就使用奈米金來製作，利用的就是孕婦體內有特殊荷爾蒙HCG使得奈米金粒子顆粒改變呈現紅色的特殊原理。

During the Lunar New Year and New Year's Day, we often witness the beautiful display of fireworks. But have we ever wondered about the profound chemical principles behind these captivating displays?

The chemical principles behind fireworks are similar to those of firecrackers, as they both involve the use of gunpowder and fuses. When a firework is ignited, a chemical reaction occurs, leading to an explosion. The majority of the resulting energy is converted into light energy, which is what we see. To create a colorful display, luminous and color-producing agents are added during the production of fireworks.

The luminous effect is achieved by the oxidation of powdered metals such as magnesium or aluminum. When these metals burn, they emit intense light and heat energy. Color-producing agents consist of metal compounds that contain metal ions. When these metal ions are burned, they emit unique flame colors. Different metal compounds produce different colors of light when burned. For example, both sodium chloride and sodium sulfate are sodium compounds that produce a golden flame when burned. Similarly, calcium nitrate and calcium carbonate produce a brick-red flame when burned. Fireworks take advantage of these properties of metals. Skilled fireworks makers carefully arrange the sequence of combustion to create the desired patterns. As a result, fireworks ignite and explode in a specific order, creating a spectacular display of vibrant, multicolored patterns against the dark night sky.

The diverse range of flame colors produced by different metal ions during combustion allows for the creation of various stunning fireworks displays.

As we gaze upon the beautiful fireworks, let us not forget the dedicated efforts of the scientists who have worked tirelessly to develop these captivating pyrotechnic wonders!

Hair strands, bloodstains, and clothing fibers are all crucial pieces of evidence that help law enforcement officers uncover the truth behind a crime. The field of forensic science utilizes these "trace evidence" to investigate the cause and process of a crime. Through the analysis of these trace evidence, forensic experts can present them as incriminating evidence in court. Hence, "forensic" in the term carries the connotation of being applicable in a legal setting. Forensic scientists process and analyze the evidence collected from the crime scene. They observe, classify, compare, and utilize advanced scientific methods to measure, estimate, interpret data, and ultimately draw reasonable conclusions to present in court. 

The Hong Kong Government Laboratory's Forensic Science Division, which obtained accreditation from the "American Society of Crime Laboratory Directors/Laboratory Accreditation Board" in 1996, has become one of the most prominent forensic science laboratories in the Asia-Pacific region.

How do forensic analysts use scientific methods to analyze "fingerprint, bloodstain, and unknown substances" and turn them into evidence in court?

Fingerprints are the most common pieces of evidence found at crime scenes. Due to the unique patterns of each person's fingerprints, they become essential clues in identifying suspects. Whenever a person touches an object, the uneven surface of the fingertips leads to the transfer of chemicals. Fingerprints usually contain around 1 milligram of substances, primarily composed of sweat (99% water and salt) and trace amounts of amino acids, urea, and oily substances transferred from other parts of the body.

Visible fingerprints are left on hard, non-porous, and smooth surfaces. These fingerprints can be easily visualized and photographed by using white or black powders. Invisible fingerprints are left on soft, porous, and rough surfaces. A common method to reveal these invisible fingerprints is through cyanoacrylate fuming. This method produces white synthetic materials that render the invisible fingerprints visible to the naked eye.

Bloodstains are also common evidence found at crime scenes. Bloodstain pattern analysis can aid in reconstructing and confirming or refuting testimonies. Bloodstains found at the crime scene can be used to extract DNA evidence for comparison with the DNA of suspects and victims. In DNA profiling analysis, forensic scientists use the polymerase chain reaction (PCR) to amplify the DNA samples extracted from blood or bloodstains. The DNA fragments are then cut into different sizes, separated, and arranged according to their sizes to form a DNA profile. These profiles constitute the DNA fingerprint. In a homicide case, bloodstains on the suspects' bodies or clothing are collected and compared to the DNA profile of the victim. If the DNA profiles match or are sufficiently similar, these results can be used as legally admissible evidence in a prosecution.

Forensic scientists often need to analyze unknown substances. These substances may include drugs found on suspects involved in drug use or trafficking or flammable materials found in suspicious fire scenes. They may also include residue powder collected from explosion or shootout scenes.

Currently, various experimental methods have been developed to analyze different characteristics of substances. From the first case of determining the guilt of a suspect in the "paper box corpse" using forensic methods more than a decade ago to the popular "Forensic Heroes" TV drama series, the general public now has a preliminary understanding of forensic science. However, the science involved in forensic analysis is deep and intricate. It awaits further exploration by students with an interest in and passion for science.

In theory, any spontaneous redox reaction can be designed as a primary battery. However, in practice, certain requirements need to be met for a primary battery to be suitable as a power source. These requirements include achieving a certain voltage, having a relatively large capacity, being economical, and convenient to carry. Various types of chemical batteries have been developed for different purposes. Below, I will introduce several commonly used ones:

1. Dry Cell

The dry cell commonly used in flashlights and small devices has a zinc casing as the negative electrode. The carbon rod in the center acts as the positive electrode. It is surrounded by a mixture of graphite powder and manganese dioxide powder, which serves as a filler. The space between the positive and negative electrodes is filled with an aqueous solution of zinc chloride and ammonium chloride, which acts as the electrolyte. To prevent leakage, the electrolyte is often mixed with a starch-based paste. The discharge reactions in the battery are as follows:

Negative Electrode: Zn - 2e → Zn2+

Positive Electrode: 2NH4+ + MnO2 + 2e → 2NH3 + MnO + H2O

Overall Battery Reaction: Zn + 2NH4Cl + MnO2 → ZnCl2 + 2NH3 + MnO + H2O

The ammonia produced at the positive electrode forms a gaseous insulating layer around the carbon electrode. This can be prevented by the migration of Zn2+ ions to the carbon electrode, where they react with ammonia molecules to form complex ions such as [Zn(NH3)4]2+.

The electromotive force (EMF) of a new dry cell is approximately 1.5V. Such dry cells are considered "primary" batteries, meaning they cannot be recharged or regenerated.

2. Rechargeable Battery

Rechargeable batteries can be recharged and regenerated. When they discharge, a spontaneous reaction occurs, acting as a galvanic cell. During charging, an electrolysis reaction takes place, acting as an electrolytic cell, which allows the original reactants to regenerate.

One of the most commonly used rechargeable batteries in automobiles is the lead-acid battery. It consists of alternating sponge-like lead plates and lead dioxide plates immersed in sulfuric acid solution. During battery discharge, the following reactions occur:

Negative Electrode (Pb): Pb + SO4^2- - 2e → PbSO4

Positive Electrode (PbO2): PbO2 + 4H+ + SO4^2- + 2e → PbSO4 + 2H2O

Overall Reaction: Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O

As evident from the reactions, lead sulfate is formed on both electrodes. Due to its low solubility, it deposits on the electrodes rather than dissolving in the solution. Since sulfuric acid is consumed and water is generated in the reaction, the discharge level of the battery can be determined by measuring the density of sulfuric acid. When the density of sulfuric acid drops to 1.05 g·mL^-1 or the voltage decreases to 1.9V, the battery needs to be recharged.

During battery charging, a direct current is applied. The lead plate is connected to the negative terminal of the power source, and the lead dioxide plate is connected to the positive terminal. In the electrolysis process, the electrode reactions mentioned above proceed in the reverse direction:

Anode (PbO2): PbSO4 + 2H2O - 2e → PbO2 + 4H+ + SO4^2-

Cathode (Pb): PbSO4 + 2e → Pb + SO4^2-

Overall Reaction: 2PbSO4 + 2H2O → Pb + PbO2 + 2H2SO4

Hence, the reaction for this lead-acid battery can be represented as:

Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O

After charging, the electromotive force (EMF) of a single lead-acid battery is approximately 2.1V. In automobiles, six batteries are connected in series, resulting in a total voltage of approximately 12V.

3. Fuel Cell

If the oxidation-reduction reactions of fuels such as H2, CO, CH4, etc., occur in a battery device, the chemical energy can be directly converted into electrical energy. Such batteries are called fuel cells.

The Apollo spacecraft, for example, used hydrogen fuel cells. The negative electrode is a porous nickel electrode, and the positive electrode is a nickel electrode covered with nickel oxide. An electrolyte solution of KOH is used. The electrode reactions are as follows:

Negative Electrode: 2H2 - 4e + 4OH- → 4H2O

Positive Electrode: O2 + 2H2O + 4e → 4OH-

Overall Reaction: 2H2 + O2 → 2H2O

The significant significance of fuel cells is the direct conversion of chemical energy into electrical energy. Currently, the vast majority of electrical energy is generated by steam turbines, which rely on the combustion of coal, oil, or natural gas. The conversion of chemical energy into electrical energy in this case is indirect: the chemical energy is first converted into heat, and then the heat is used to generate steam. This indirect process is less efficient both theoretically and practically compared to the direct process of a battery. The best power plants can only convert 30% to 40% of the heat from fuel combustion into electrical energy, with the remaining portion being lost as waste heat to the air and water, leading to thermal pollution. Fuel cells, on the other hand, can bypass the limitations of thermal efficiency since the current is generated directly. The theoretical efficiency of fuel cells can reach 100%, and practical fuel cells have achieved efficiencies of up to 75%. Therefore, fuel cells are ideal and highly efficient energy devices, significantly reducing the thermal pollution associated with power generation. Hydrogen fuel cells are a successful and pollution-free new energy source.

Posted in: http://www.npc.edu.hk/~chem/theory/sciene.htm

Fireflies are capable of producing light through a phenomenon called bioluminescence. The specific mechanism behind their bioluminescence involves a chemical reaction between luciferin and luciferase enzymes. The light-emitting organs of fireflies, located in their abdomen, contain these chemicals. The process can be summarized as follows:

Luciferin: Fireflies produce a molecule called luciferin, which serves as the light-emitting pigment.

Luciferase: They also produce an enzyme called luciferase, which acts as a catalyst for the light-emitting reaction.

Oxygen and ATP: The reaction requires oxygen and adenosine triphosphate (ATP), which is an energy-carrying molecule.

Oxidation reaction: When luciferin combines with oxygen and ATP in the presence of luciferase, it undergoes an oxidation reaction. This reaction releases energy in the form of light.

The purpose of firefly bioluminescence is primarily related to mating and communication. Fireflies use their light-emitting abilities to attract potential mates. Each species of firefly has a unique flashing pattern or rhythm that acts as a specific signal for recognition. The flashing patterns help fireflies of the same species find and identify each other in the darkness, enabling them to come together for mating.

It's worth noting that the light emitted by fireflies is often referred to as "cold light" because it produces minimal heat. The energy conversion in fireflies is highly efficient, with only a small percentage (about 2-10%) of the energy converted into heat, while the rest is used for light production. This efficiency makes firefly bioluminescence an intriguing natural phenomenon.