Name: how dyes absorb visible light
Uploaded: 2020-03-26T07:22:29.000Z
Duration: 4 min 55 s
Channel: JoVE

光が物質に到達すると、一部はそれに吸収され、残りはそれを介して反射または透過されます。私たちが知覚する物質の色は、それが反射する可能性が最も高い波長によって異なります。たとえば、私たちが青く見える生地には、青色光を強く反射し、オレンジ色と赤色の光を強く吸収する染料が含まれています。
染料は通常、共役化合物であり、二重結合と単結合が交互に存在します。電子は共役系内を自由に移動できます。異なる色の染料は、吸収する光の波長が異なる必要があります。いくつかの例を見ると、吸収される波長は共役の量とともに増加することがわかります。
では、波長は共役の程度とどのように関連しているのでしょうか。分子エネルギーレベルを考えてみましょう。非局在化電子は、分子軌道(MO)を占めると考えることができます。分子は、電子をより高いエネルギーの分子軌道に励起するために必要な正確なエネルギーで光を吸収します。最も可能性の高い遷移は、HOMOと呼ばれる最も高い占有分子軌道から、最も低い非占有分子軌道(LUMO)への遷移です。したがって、最も吸収される波長はHOMO-LUMOのエネルギーギャップと一致すると予想されます。
コンジュゲーションがほとんどまたはまったくない分子は、通常、HOMO - LUMOギャップが大きくなります。紫外線を吸収し、すべての可視光線を反射するため、白色または無色に見えます。共役結合は、特に高エネルギーで分子のエネルギーレベルを下げることにより、分子を安定化させます。コンジュゲーションの度合いが高いほど、HOMO-LUMOギャップは小さくなり、吸収波長が大きくなります。金属と置換もギャップに影響します。
例を見てみましょう。レチノールは小さな共役系を持ち、クロロフィルaは窒素とマグネシウムを含む大きな系を持っています。レチノールは325 nmで吸収され、クロロフィルAは430 nmと662 nmの両方で吸収されます。予想通り、レチノールのエネルギーギャップは大きくなります。
紫外線や可視光線、またはUV-Vis分光光度計を使用して吸収を調べることができます。分光光度計は、光源、サンプルが受け取る波長を制御する方法、および光検出器で構成されています。通常、サンプルは透明な溶液です。吸光度は、特定の波長で測定することも、化合物が複数の波長で吸収することが多いため、波長範囲で測定することもできます。さらに、分子の向きや振動状態が異なるため、各遷移にはさまざまな波長が見られます。
測定中、光は吸収されるか、分子に接触せずに通過するか、溶媒または化合物分子に跳ね返ります。逆方向に跳ね返る少量の光は無視します。分子に吸収される可能性のある光が、代わりに分子に跳ね返ることがあります。物質が特定の波長を独自のモル減衰係数でどれだけうまく透過するかを説明します。吸光度は濃度によって変化しますが、モル減衰係数は変化しません。
測定後、分光光度計は、透過率と呼ばれる比率で受信した光と元の光を比較します。吸光度は、透過率の負の基数 10 対数です。分光光度計に溶媒の吸光度がある場合は、それを差し引いて化合物のみを表示します。通常、結果は吸光度対波長として表示されます。化合物が最も吸収する波長は、ラムダマックスと呼ばれます。各波長のモル減衰係数を計算すると、ラムダ最大で最高になります。
モル減衰係数、吸光度、サンプル濃度、および光路長(光がサンプルを通過した距離)は、ランベルトベールの法則によって関連付けられています。任意の3つの変数がわかっている場合、4番目の変数を計算できます。
このラボでは、UV-Vis分光光度計を使用して、フルオレセイン、ベータカロチン、およびインディゴ色素の吸収特性を分析します。次に、ランベルト ベールの法則を使用して β-カロチンの検量線を作成し、β-カロチン溶液の濃度を決定します。

染料のuv-vis分光法

吸光度
光が物質と相互作用すると、光の一部が吸収され、残りは反射または透過されます。私たちが色を持っていると認識している物質は、可視範囲の光を反射します。私たちが見ることができる物質の色は、反射される光の波長によって異なります。私たちが青く知覚する物質は、可視スペクトルの青色範囲(430〜480 nm)の光を反射します。カラーホイールによると、同じ物質が反射光を補完する光を吸収します。したがって、青い物質は可視スペクトルのオレンジ領域(590〜630 nm)の光を吸収します。すべての化合物が可視領域に吸収されるわけではなく、その結果、人間の目には無色に見えます。
光は、そのエネルギーEと波長λによって定義されます。ここで、hはプランク定数、cは光速です。
<img src="/CDNSource/lm/labs/70/70_Concepts_1.jpg" alt="エネルギー方程式 \(E = \frac{hc}{\lambda}\)、式、波長、光子エネルギーの計算" data-altupdatedat="1754907201000">
光の波長は、そのエネルギーに反比例します。したがって、高エネルギーの光は波長が短くなります。
<h4>染料</h4>
色の染料が異なれば、吸収する光の波長も異なります。ほとんどの染料は、二重結合と単結合が交互に交差する共役化合物であり、通常は可視領域の光を吸収します。
色素分子の共役部分は非常に短く、結合度が低く、二重結合と単結合が交互に結合することが少ない場合もあれば、長い結合(二重結合と単結合が交互に多く存在する高度な結合があることを意味する)があります。これらの交互の二重結合は、必ずしも2つの炭素の間だけにある必要はありません。これらの共役結合には、カルボニル基や炭素と酸素の二重結合が含まれます。共役の程度は、化合物が吸収する光の波長を決定します。例えば、コンジュゲーションの度合いが高い化合物は、コンジュゲーションの度合いが低いコンパウンドよりも長い波長を吸収します。
分子軌道理論に基づくと、非局在化電子が分子軌道を占めます。最高占有分子軌道(HOMO)は、電子を持つ最高エネルギー軌道です。最も低い空いている分子軌道(LUMO)は、電子のない最も低いエネルギー軌道です。コンジュゲーションがほとんどまたはまったくない分子は、通常、HOMOとLUMOの間に大きなエネルギーギャップがあります。しかし、共役分子は、HOMOとLUMOの間のエネルギーギャップが小さくなります。
電子を低いエネルギー準位から高いエネルギー準位へ、またはHOMOからLUMOへ励起するためには、分子は2つの軌道間のエネルギーギャップに等しいエネルギーで光を吸収しなければならない。このため、エネルギーギャップの大きい分子は、電子を励起するために紫外線などの高エネルギー光を必要とします。しかし、染料はエネルギーギャップが小さく、電子を励起するために可視光などの低エネルギー光を必要とします。
<img src="/CDNSource/lm/labs/70/70_Concepts_2.jpg" alt="エネルギーギャップ方程式ΔE(HOMO-LUMO)= hc / λ;分子分光法,量子化学。" data-altupdatedat="1754907201000">
このため、エネルギーギャップの大きい分子は、電子を励起するために紫外線などの高エネルギー光を必要とします。しかし、染料はエネルギーギャップが小さく、電子を励起するために可視光などの低エネルギー光を必要とします。
光のエネルギーは波長に反比例することを思い出してください。したがって、高エネルギー光は、波長が長い低エネルギー光よりも波長が短くなります。
<h4>分光 光度 計</h4>
実験的には、光吸光度は紫外可視(UV-Vis)分光光度計を使用して測定されます。この装置は、モノクロメーターによって特定の波長の光に変換され、サンプルを通過してもう一方の端の検出器に入る光源を利用しています。サンプルは液体中にある必要があるため、有機化合物が固体の場合は溶媒が必要です。この溶液は、キュベットと呼ばれるサンプルホルダーに保持されます。サンプルに応じて、キュベットは水晶、ガラス、またはプラスチックでできており、特定の光路長があります。このパス長は、光がサンプルを通過する必要がある距離です。溶媒は光も吸収するため、溶媒のサンプルブランクのみが必要です。したがって、装置がサンプル化合物の吸光度スペクトルを捕捉すると、溶媒のバックグラウンドスペクトルを差し引いて、サンプルのみによって引き起こされる吸光度を表示できます。透過率Tは、サンプルを通過する元の光の割合です。
<img src="/CDNSource/lm/labs/70/70_Concepts_3.jpg" alt="透過率方程式T=P/P₀式は分光分析と光学研究の鍵" data-altupdatedat="1754907201000">
ここで、P0は、サンプルに当たる前の光ビームの放射照度、または単位面積あたりの1秒あたりのエネルギーです。Pは、検出器に当たる光ビームの放射照度です。Pは通常、光の一部がサンプルに吸収されるため、P0より低くなります。
吸光度Aは、透過率の負の対数として定義されます。
<img src="/CDNSource/lm/labs/70/70_Concepts_4.jpg" alt="吸光度式:A = log(P ₀ / P)=-logT;分光分析における光学原理" data-altupdatedat="1754907201000">
吸光度の値の範囲は 0 (吸収なし) から 2 (99% の吸収) です。光が吸収されないとき、P0はPに等しく、透過率は1に等しくなります。したがって、吸光度はゼロです。光の90%が吸収されると、10%が透過し、Tは0.1に等しくなります。この結果、吸光度は 1 に等しくなります。光の99%が吸収されると、1%が透過し(T = 0.01)、吸光度は2に等しくなります。
得られるスペクトルは、吸光度と波長のプロットです。UV-Vis分光光度計の場合、この範囲は200〜800nmです。
<h4>ランベルトビールの法則</h4>
特定の化合物の透過率と吸光度は、溶液中の化合物の濃度に関連しています。この関係は、ランベルトビールの法則によって説明されています。
<img src="/CDNSource/lm/labs/70/70_Concepts_5.jpg" alt="ビール・ランバートの法則方程式; A=εcl;分光法における吸収の図。光学研究。" data-altupdatedat="1754907201000">
サンプルの吸光度は、化合物の濃度、光路長、およびモル減衰係数の積に等しくなります。この係数は各化合物に固有であり、波長によって異なります。ただし、波長を一定に保つと、濃度の変化に関係なく、モル減衰係数は同じになります。サンプルの最大吸光度に対応する波長(λmax)も、最大のモル減衰係数を持ちます。
<h4>参照</h4>
<ol>
	<li style="font-size:17px">Silberberg, M.S. (2012).化学:物質と変化の分子的性質。マサチューセッツ州ボストン:マグロウヒル。</li>
	<li style="font-size:17px">ハリス、ワシントンD.C.(2015年)。 定量的化学分析。 ニューヨーク州ニューヨーク:WHフリーマンアンドカンパニー。</li>
</ol>

染料のUV-Vis分光法

吸光度
光が物質と相互作用すると、光の一部が吸収され、残りは反射または透過されます。...

Education

JoVE Lab Manual

Chemistry

化学

UV-Vis Spectroscopy of Dyes

how dyes absorb visible light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and wavelength, and higher-energy light has a shorter wavelength.

Most dyes are conjugated compounds. This means they contain alternating double and single bonds, and in some cases carbonyl groups and carbon-oxygen double bonds also take part in the conjugated system. The length of the conjugated region affects the wavelength the dye absorbs. A dye with more conjugation absorbs a longer wavelength than a dye with less conjugation. This happens because delocalized electrons occupy molecular orbitals. The highest occupied molecular orbital, or HOMO, is the highest-energy orbital with an electron, and the lowest unoccupied molecular orbital, or LUMO, is the next available empty orbital.

Molecules with little or no conjugation usually have a large energy gap between the HOMO and LUMO. Conjugated molecules have a smaller gap. An electron must absorb light with the same energy as that gap to move from the HOMO to the LUMO. Because of this, molecules with a large gap need higher-energy UV light, while dyes with a smaller gap can be excited by lower-energy visible light. Since light energy and wavelength are inversely related, higher-energy light has a shorter wavelength.

Absorbance is measured experimentally with a UV-Visible, or UV-Vis, spectrophotometer. The instrument uses a light source and a monochromator to select specific wavelengths. That light passes through a liquid sample and then reaches a detector. If the compound is a solid, it must first be dissolved in a solvent. The solution is placed in a cuvette, which may be made of quartz crystal, glass, or plastic. The cuvette has a pathlength, which is the distance the light travels through the sample. Because the solvent also absorbs light, a blank made of solvent alone is used to subtract background absorbance.

The instrument measures transmittance, which is the fraction of the original light that passes through the sample. P0 is the irradiance before the sample, and P is the irradiance that reaches the detector. Absorbance is the negative log of transmittance. It ranges from 0, which means no absorption, to 2, which means 99% absorption. If 90% of the light is absorbed, transmittance is 0.1 and absorbance is 1. If 99% is absorbed, transmittance is 0.01 and absorbance is 2. The spectrum is a plot of absorbance versus wavelength, and for UV-Vis spectroscopy, the range is 200 to 800 nm.

The amount of light absorbed by a dye also depends on its concentration in solution. This relationship is described by the Beer-Lambert law. Absorbance equals the concentration of the compound multiplied by the path length and the molar attenuation coefficient. The molar attenuation coefficient is unique to each compound and changes with wavelength. If the wavelength is kept constant, it does not change with concentration. The wavelength with the highest absorbance is called lambda max, and it also has the largest molar attenuation coefficient.

How Dyes Absorb Visible Light

lab techniques

Measuring with Accuracy in the Lab

Measuring with accuracy in the lab starts with careful records, the right tools, and correct reading of data. Scientists use lab notebooks to record how an experiment was done. These notes include the amounts of materials used and each step of the procedure. Without that record, an experiment cannot be repeated in the same way. Balances and glassware are used to measure solids and liquids for experiments. The precision of a measurement depends on the equipment used. Digital balances show the...

scientific measurement and lab skills

Graphs, Curve Fit, and Standard Deviation

Two-dimensional graphs help students compare an independent variable with a dependent variable in science data. In a chemistry example, temperature is the independent variable and volume is the dependent variable. After data are collected, the relationship between the two measurements must be quantified so it can be evaluated and compared with other relationships. A graph can also show when no relationship exists between the two variables. To make a two-dimensional graph, each data point needs...

stoichiometry, product yield, and limiting reactants

stoichiometry-product-yield-and-limiting-reactants

Balancing Equations and Reactant Limits

Chemical equations show how reactants change into products during a reaction. Stoichiometry is the study of the relative amounts of reactants and products. It is based on the Law of Conservation of Mass, which says matter is neither created nor destroyed. Because atoms are only rearranged, the number and identity of atoms must match on both sides of a reaction. That is why a chemical equation must be balanced. A balanced equation has the same number of atoms for each element in the reactants...

redox reactions

Oxidation States in Redox Reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number. Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding...

ideal gas law

Gas Laws Behind the Ideal Gas Equation

The ideal gas equation brings together the main gas laws used in chemistry. Gases have molecules that are far apart, so their behavior is described with four measurable variables: pressure, volume, number of moles, and temperature. The ideal gas law links these variables with the gas constant, R, which equals 8.314 J·K−1 mol−1. Boyle’s law describes the link between pressure and volume. When temperature and the number of moles stay constant, pressure and volume change in opposite directions.

acid and base concentrations

Acids, Bases, and pH in Titration

Acids, bases, and pH explain how acidic or basic a solution is. An Arrhenius acid releases hydrogen ions when it dissolves in water, while an Arrhenius base releases hydroxide ions. These reactions also create conjugate partners: an acid forms a conjugate base after losing hydrogen, and a base forms a conjugate acid after losing hydroxyl. Every acid has a conjugate base, and every base has a conjugate acid. pH measures the amount of hydrogen ions in a solution. The pH scale runs from 0 to 14...

buffers

Buffer pH and the Common Ion Effect

Buffer solutions help keep pH steady when acids or bases are added. In water, an Arrhenius acid (HA) dissociates into hydrogen ions, H+, and a conjugate base, A-. More hydrogen ions make a solution more acidic and lower its pH. An Arrhenius base (BOH) dissociates into a conjugate acid, B+, and hydroxide ions, OH-. Strong acids and strong bases usually change pH a lot because they react completely in water and raise the amount of H+ or OH-. Buffers reduce those pH changes. A buffer usually...

enthalpy of reaction

Reaction Heat, Hess’s Law, and Calorimetry

Reaction heat is explained through enthalpy, Hess’s law, and calorimetry. These ideas show how heat moves during chemical reactions and how scientists measure it. Thermodynamics is the study of heat energy and other forms of energy, such as work. Its laws are used across science, from biology to physics. The first law says energy is conserved in an isolated system. Energy can change form, such as thermal energy becoming work, but it cannot be created or destroyed. The second law of...

solubility

Solubility in Water and Other Solvents

Solubility describes how much of a solute can dissolve in a specific solvent. It is usually reported as solute mass per solvent volume or as solute mass per solvent mass. For example, sodium chloride has a solubility of 36 g per 100 mL of water at room temperature. If solubility is given by solvent mass, that mass must be converted to volume for later calculations. Temperature changes solubility. Sodium carbonate dissolves at about 7 g per 100 mL of water at 0 °C, 22 g per 100 mL at room...

metal flame emission

Flame Test Metal Color Clues

Flame testing uses a metal sample and a flame to identify a substance by its color. Each element gives off a characteristic light emission in the flame, so the color can help distinguish one element from another. This same idea appears in fireworks, where different metal components create different colors. The color comes from energy absorbed by the metallic component. When a species absorbs energy, that energy can go into translation, vibration, rotation, or electron excitement. Electron...

balmer series

Hydrogen Emission Lines

Hydrogen emission lines show how electrons move between fixed energy levels in the Bohr model. Niels Bohr proposed this model for the hydrogen atom in 1913. In this model, an electron can only occupy certain orbits, and it cannot exist between them. These energy states are labeled with the quantum number n. The ground state is n = 1. Higher values, such as n = 2, 3, 4, and so on, are excited states. An electron changes state only by absorbing or emitting energy equal to the difference between...

beer's law

Absorbance Spectra and Beer-Lambert Analysis

Absorbance spectra and the Beer-Lambert Law show how light can be used to study molecules in solution. When light hits a substance, it may be absorbed, transmitted, or reflected. A substance often interacts with a range of wavelengths, and each wavelength can affect the molecules or atoms in a different way. When a molecule absorbs light, that energy can be used for translation, vibration, rotation, or electron excitement. Electron excitement is especially important in spectroscopy because it...

concentration dependence

Reaction Order and Rate Constants

Chemical kinetics describes the speed of a chemical reaction. The rate depends on the reaction mechanism, the complexity of the reaction, and the number of reactants involved. Reactant concentration also affects how fast a reaction happens. The rate law is the experimental relationship that connects these factors to reaction rate. In the rate law, each reactant contributes through a reaction order. The general form is r = k[A]^m[B]^n for aA + bB + ... → cC. Here, r is the reaction rate, k is...

temperature dependence

Reaction Rate, Arrhenius, and Catalysts

Chemical kinetics explains how fast a reaction happens and why that speed changes. The reaction rate is the speed of a chemical reaction. It is defined as the change in concentration of a reactant or product over time. Reaction speed depends on several factors, including the concentration of the reactants and the temperature of the reaction. Each reactant affects the rate in a specific way. That relationship is described by the rate law. The rate law is an equation that connects the...

galvanic cells

Battery Power from Redox Reactions

Electrochemistry studies how chemical change and electrical energy are linked. In this branch of chemistry, electrons move from one species to another. That movement can either produce current or be driven by an applied current. The main reaction in electrochemistry is the oxidation-reduction, or redox, reaction. A redox reaction has two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. These changes also shift the oxidation state of each substance. The...

electrolytic cells

Electroplating with Electrolytic Cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the...

proper lab notebook keeping

Recording a Reproducible Lab Experiment

Accurate lab notebook records are essential in science and organic chemistry labs. Without clear notes, descriptions, quantities, and observations, an experiment cannot be repeated or checked. Good record keeping supports reproducibility, which means other people can follow the same work and get similar results. A laboratory notebook is useful in school labs, research settings, and industry. It can also become a legal record when an idea, process, substance, or technique is patented and...

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

Organic chemistry labs use specific glassware, careful weighing steps, and controlled heating to keep reactions safe and accurate. Beakers and Erlenmeyer flasks are often used for mixing or holding solvents, but they are not meant for measuring volume unless only an approximate amount is needed. Volumetric glassware is used when a precise volume matters. This group includes graduated cylinders, volumetric pipettes, and volumetric flasks. A graduated cylinder is commonly used in the organic lab...

melting points

How Impurities Change Melting Points

Melting point helps identify an organic compound by showing the temperature where a solid turns into a liquid at 1 atmosphere of pressure. It is a physical property, like solubility, density, color, and electronegativity. Because the exact start of melting is hard to measure, the result is reported as a range. The lower end is when the first drops of liquid appear. The upper end is when the last solid has melted. Scientists compare this range with literature values to help identify a compound. <br...

boiling points

Boiling Point and Vapor Pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

入門化学ラボコースの指導者と学生のための、包括的でカリキュラムに焦点を当てたビデオ。

https://cloudfront.jove.com/files/banners/scicat/labbio.jpg

Learn how dye structure affects visible light absorption, how UV-Vis spectrophotometers measure absorbance, and how Beer-Lambert law links absorbance to concentration.

How Dyes Absorb Visible Light | JoVE K12

染料のUV-Vis分光法 を教える準備を、この 4 分間の教員向けガイドで行いましょう。JoVE Lab Manual の Chemistry ラボの主要な準備手順を解説します。

Chemistry の 染料のUV-Vis分光法 教員準備 - 8.8K+ 回の視聴 | JoVE Lab Manual

この 10 分間の学生プロトコル動画で、染料のUV-Vis分光法 の手順をステップごとに学びましょう。JoVE Lab Manual の Chemistry コレクションの一部です。

Chemistry の 染料のUV-Vis分光法 学生プロトコル - 37K+ 回の視聴 | JoVE Lab Manual

How Dyes Absorb Visible Light

Description

Transcript

Tags