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

Işık bir maddeye ulaştığında, bir kısmı onun tarafından emilirken, geri kalanı ya yansıtılır ya da onun aracılığıyla iletilir. Maddenin rengi, algıladığımız şekliyle, hangi dalga boylarını yansıtma olasılığının en yüksek olduğuna bağlıdır. Örneğin, mavi olarak gördüğümüz bir kumaş parçası, mavi ışığı güçlü bir şekilde yansıtan ve turuncu ve kırmızı ışığı güçlü bir şekilde emen bir boya içerir.
Boyalar tipik olarak konjuge bileşiklerdir, yani alternatif çift ve tek bağlara sahiptirler. Elektronlar konjuge sistem içinde serbestçe hareket edebilir. Farklı renkteki boyalar, emdikleri ışığın dalga boylarında değişiklik göstermelidir. Birkaç örneğe baktığımızda emilen dalga boyunun konjugasyon miktarı ile arttığını görürüz.
Peki, dalga boyu konjugasyon derecesi ile nasıl ilişkilidir? Moleküler enerji seviyelerini ele alalım. Delokalize elektronları işgal eden moleküler orbitaller veya MO'lar olarak düşünebiliriz. Bir molekül, bir elektronu daha yüksek enerjili bir moleküler orbitale uyarmak için gereken tam enerjiye sahip ışığı emer. En olası geçiş, HOMO adı verilen en yüksek dolu moleküler orbitalden en düşük boş moleküler orbitale veya LUMO'ya geçiştir. Bu nedenle, en çok emilen dalga boyunun HOMO - LUMO enerji boşluğu ile eşleşmesini bekliyoruz.
Konjugasyonu çok az olan veya hiç olmayan moleküller tipik olarak büyük bir HOMO - LUMO boşluğuna sahiptir. UV ışığını emerler ve tüm görünür ışığı yansıtırlar, böylece beyaz veya renksiz görünürler. Konjuge bağlar, özellikle yüksek enerjilerde enerji seviyelerini düşürerek molekülleri stabilize eder. Konjugasyon derecesi ne kadar yüksek olursa, HOMO - LUMO boşluğu o kadar küçük ve emilen dalga boyu o kadar büyük olur. Metaller ve ikameler de boşluğu etkiler.
Bir örneğe bakalım. Retinol küçük bir konjuge sisteme sahipken, klorofil a nitrojen ve magnezyum içeren büyük bir sisteme sahiptir. Retinol 325 nm'de absorbe ederken, klorofil a hem 430 hem de 662 nm'de absorbe eder. Beklendiği gibi, retinolün enerji açığı daha büyüktür.
Bir UV ve görünür ışık veya UV-Vis spektrofotometresi kullanarak absorpsiyonu inceleyebiliriz. Bir spektrofotometre, bir ışık kaynağı, numunenin aldığı dalga boylarını kontrol etmenin bir yolu ve bir ışık dedektöründen oluşur. Numune tipik olarak şeffaf bir çözeltidir. Absorbans, belirli bir dalga boyunda ölçülebilir veya bir dalga boyu aralığında ölçülebilir, çünkü bileşikler genellikle birden fazla dalga boyunda absorbe eder. Ek olarak, moleküller farklı yönelimlerde ve titreşim durumlarında olduğu için her geçiş için bir dizi dalga boyu görüyoruz.
Ölçüm sırasında ışık ya emilir, herhangi bir moleküle temas etmeden geçer ya da bir çözücü veya bileşik molekülden seker. Geriye doğru yansıyan az miktarda ışığı görmezden geliyoruz. Bazen, bir molekül tarafından emilebilen ışık, bunun yerine ondan yansır. Bir maddenin belirli bir dalga boyunu benzersiz bir molar zayıflama katsayısı ile ne kadar iyi ilettiğini açıklıyoruz. Absorbans konsantrasyon ile değişirken, molar zayıflama katsayısı değişmez.
Ölçümden sonra spektrofotometre, alınan ve orijinal ışığı geçirgenlik adı verilen bir oranda karşılaştırır. Absorbans, geçirgenliğin negatif baz 10 logaritmasıdır. Spektrofotometre çözücünün absorbansına sahipse, sadece bileşiği göstermek için onu çıkarır. Sonuçlar genellikle dalga boyuna karşı absorbans olarak görüntülenir. Bileşiğin en çok emdiği dalga boyuna lambda max denir. Her dalga boyu için molar zayıflama katsayısını hesaplasaydık, lambda maks'ta en yüksek olurdu.
Molar zayıflama katsayısı, absorbans, numune konsantrasyonu ve ışığın numune boyunca kat ettiği mesafe olan yol uzunluğu, Beer-Lambert yasası ile ilişkilidir. Herhangi üç değişkeni biliyorsak, dördüncüsünü hesaplayabiliriz.
Bu laboratuvarda, bir UV-Vis spektrofotometresi kullanarak floresein, beta karoten ve indigo boyanın absorpsiyon özelliklerini analiz edeceksiniz. Daha sonra bir β-karoten kalibrasyon eğrisi oluşturmak için Beer-Lambert yasasını kullanacak ve ardından β-karoten çözeltisinin konsantrasyonunu belirleyeceksiniz.

boyaların uv-vis spektroskopisi

Emicilik
Işık bir madde ile etkileşime girdiğinde, ışığın bir kısmı emilirken, geri kalanı ya yansıtılır ya da onun aracılığıyla iletilir. Bir renge sahip olarak algıladığımız maddeler, görünür aralıktaki ışığı yansıtır. Görebildiğimiz maddenin rengi, hangi dalga boyundaki ışığın yansıtıldığına bağlıdır. Mavi olarak algıladığımız bir madde, görünür spektrumun mavi aralığındaki (430 – 480 nm) ışığı yansıtır. Renk çarkına göre, aynı madde yansıyan ışığı tamamlayan ışığı emer. Böylece mavi madde, görünür spektrumun turuncu bölgesindeki (590 – 630 nm) ışığı emer. Tüm bileşikler görünür bölgede emilmez ve sonuç olarak insan gözüne renksiz görünürler.
Işık, enerjisi E ve dalga boyu λ ile tanımlanır. Burada, h Planck sabiti ve c ışık hızıdır.
<img src="/CDNSource/lm/labs/70/70_Concepts_1.jpg" alt="Enerji denklemi \(E = \frac{hc}{\lambda}\), formül, dalga boyu, foton enerjisi hesaplaması" data-altupdatedat="1754907201000">
Işığın dalga boyu, enerjisi ile ters orantılıdır. Bu nedenle, daha yüksek enerjili ışığın dalga boyu daha kısadır.
<h4>Boya</h4>
Farklı renkteki boyalar, emdikleri ışığın dalga boyuna göre değişir. Boyaların çoğu, alternatif çift ve tek bağlara sahip konjuge bileşiklerdir ve tipik olarak görünür bölgedeki ışığı emer.
Boya molekülünün konjuge kısmı çok kısa olabilir, yani düşük derecede bir konjugasyon derecesi ve az sayıda alternatif çift ve tek bağ vardır veya uzun, yani birçok alternatif çift ve tek bağ ile yüksek derecede konjugasyon vardır. Bu alternatif çift bağların sadece iki karbon arasında olması gerekmez. Bu konjuge bağlar, karbonil gruplarını ve karbon ile oksijen arasındaki çift bağları içerebilir. Konjugasyon derecesi, bileşiğin emdiği ışığın dalga boyunu belirler. Örneğin, yüksek derecede konjugasyona sahip bileşikler, daha düşük konjugasyon derecesine sahip bileşiklerden daha uzun bir dalga boyunu emer.
Moleküler orbital teorisine dayanarak, delokalize elektronlar moleküler orbitalleri işgal eder. En yüksek işgal edilen moleküler orbital veya HOMO, bir elektron ile en yüksek enerjili orbitaldir. En düşük boş moleküler orbital veya LUMO, elektronu olmayan en düşük enerjili orbitaldir. Konjugasyonu çok az olan veya hiç olmayan moleküller tipik olarak HOMO ve LUMO arasında büyük bir enerji boşluğuna sahiptir. Bununla birlikte, konjuge moleküller, HOMO ve LUMO arasında daha küçük bir enerji boşluğuna sahiptir.
Bir elektronu daha düşük bir enerji seviyesinden daha yüksek bir enerji seviyesine veya HOMO'dan LUMO'ya uyarmak için, molekülün iki orbital arasındaki enerji boşluğuna eşit enerjiyle ışığı emmesi gerekir. Bu nedenle, büyük bir enerji boşluğuna sahip moleküller, bir elektronu uyarmak için UV ışığı gibi daha yüksek enerjili ışığa ihtiyaç duyar. Bununla birlikte, boyalar daha küçük bir enerji boşluğuna sahiptir ve bir elektronu uyarmak için görünür ışık gibi daha düşük enerjili ışığa ihtiyaç duyar.
<img src="/CDNSource/lm/labs/70/70_Concepts_2.jpg" alt="Enerji boşluğu denklemi ΔE(HOMO-LUMO) = hc/λ; Moleküler spektroskopi, kuantum kimyası." data-altupdatedat="1754907201000">
Bu nedenle, büyük bir enerji boşluğuna sahip moleküller, bir elektronu uyarmak için UV ışığı gibi daha yüksek enerjili ışığa ihtiyaç duyar. Bununla birlikte, boyalar daha küçük bir enerji boşluğuna sahiptir ve bir elektronu uyarmak için görünür ışık gibi daha düşük enerjili ışığa ihtiyaç duyar.
Işık enerjisinin dalga boyu ile ters orantılı olduğunu hatırlayın. Bu nedenle, daha yüksek enerjili ışık, daha uzun dalga boylarına sahip düşük enerjili ışıktan daha kısa dalga boylarına sahiptir.
<h4>Spektrofotometre</h4>
Deneysel olarak, ışık absorbansı bir UV-Görünür (UV-Vis) spektrofotometre kullanılarak ölçülür. Bu cihaz, bir monokromatör tarafından bir numuneden geçecek ve diğer uçtaki bir dedektöre geçecek belirli dalga boylarındaki ışığa dönüştürülen bir ışık kaynağı kullanır. Numuneler sıvı içinde olmalıdır, bu nedenle organik bileşik katı ise bir çözücü gereklidir. Bu çözelti, küvet olarak bilinen bir numune tutucuda tutulur. Numuneye bağlı olarak, küvet kuvars kristali, cam veya plastikten yapılabilir ve belirli bir yol uzunluğuna sahip olabilir. Bu yol uzunluğu, ışığın numune boyunca kat etmesi gereken mesafedir. Çözücü aynı zamanda ışığı da emeceğinden, tek başına çözücüden boş bir numune gereklidir. Bu nedenle, cihaz numune bileşiğinin absorbans spektrumunu yakaladığında, yalnızca numunenin neden olduğu absorbansı göstermek için çözücünün arka plan spektrumunu çıkarabilir. Geçirgenlik, T, numuneden geçen orijinal ışığın fraksiyonudur.
<img src="/CDNSource/lm/labs/70/70_Concepts_3.jpg" alt="Geçirgenlik denklemi T=P/P₀ formülü, spektroskopik analiz ve optik çalışmalarda anahtar." data-altupdatedat="1754907201000">
Burada, P0, numuneye çarpmadan önce ışık huzmesinin ışınımı veya birim alan başına saniye başına düşen enerjidir. P, dedektöre çarpan ışık huzmesinin ışınımıdır. Işığın bir kısmı numune tarafından emildiği için P tipik olarak P0'dan daha düşüktür.
Absorbans, A, geçirgenliğin negatif kütüğü olarak tanımlanır.
<img src="/CDNSource/lm/labs/70/70_Concepts_4.jpg" alt="Absorbans formülü: A = log (P₀ / P) = -logT; Spektroskopi analizinde optik prensipler." data-altupdatedat="1754907201000">
<h4></h4><img src="/CDNSource/lm/labs/70/70_Concepts_5.jpg" alt="Beer-Lambert yasası denklemi; A=εcl; spektroskopide absorpsiyon diyagramı; optik çalışma." data-altupdatedat="1754907201000"><h4></h4><ol><li style="font-size:17px"></li><li style="font-size:17px"></li></ol>

Boyaların UV-Vis Spektroskopisi

Emicilik
Işık bir madde ile etkileşime girdiğinde, ışığın bir kısmı emilirken, geri kalanı ya yansıtılır ya da onun aracılığıyla iletilir. ...

Education

JoVE Lab Manual

Chemistry

Kimya

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

Kimya laboratuvar temelleri için, hem eğitmenlere hem de öğrencilere yönelik, kapsamlı ve müfredat odaklı vidolar.

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

Boyaların UV-Vis Spektroskopisi öğretimine bu 4 dakikalık eğitmen rehberiyle hazırlanın. JoVE Lab Manual üzerindeki Chemistry laboratuvarı için temel hazırlık adımlarını kapsar.

Chemistry içinde Boyaların UV-Vis Spektroskopisi Eğitmen Hazırlığı - 8.8K+ Görüntülenme | JoVE Lab Manual

10 dakikalık bu öğrenci protokol videosunda Boyaların UV-Vis Spektroskopisi prosedürlerini adım adım takip edin. JoVE Lab Manual üzerindeki Chemistry koleksiyonunun bir parçasıdır.

Chemistry içinde Boyaların UV-Vis Spektroskopisi Öğrenci Protokolü - 37K+ Görüntülenme | JoVE Lab Manual

How Dyes Absorb Visible Light

Description

Transcript

Tags