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

빛이 물질에 도달하면 일부는 물질에 흡수되고 나머지는 반사되거나 전달됩니다. 우리가 인식하는 물질의 색상은 어떤 파장을 반사할 가능성이 가장 높은지에 따라 다릅니다. 예를 들어, 파란색으로 보이는 천 조각에는 청색광을 강하게 반사하고 주황색과 적색광을 강하게 흡수하는 염료가 포함되어 있습니다.
염료는 일반적으로 접합 화합물이며, 이는 이중 결합과 단일 결합이 번갈아 가며 있음을 의미합니다. 전자는 공액계 내에서 자유롭게 이동할 수 있습니다. 다른 색상의 염료는 흡수하는 빛의 파장이 다양해야 합니다. 몇 가지 예를 살펴보면 흡수된 파장이 접합의 양에 따라 증가한다는 것을 알 수 있습니다.
그렇다면 파장은 켤레의 정도와 어떤 관련이 있습니까? 분자 에너지 수준을 고려해 보겠습니다. 비편재화된 전자는 분자 궤도(molecular orbitals, MO)를 차지하는 것으로 생각할 수 있습니다. 분자는 전자를 더 높은 에너지의 분자 궤도로 여기시키는 데 필요한 정확한 에너지로 빛을 흡수합니다. 가장 가능성이 높은 전이는 HOMO라고 하는 가장 높은 점유 분자 안와에서 가장 낮은 비점유 분자 안와(LUMO)로의 전환입니다. 따라서 가장 많이 흡수된 파장이 HOMO - LUMO 에너지 갭과 일치할 것으로 예상합니다.
접합이 거의 또는 전혀 없는 분자는 일반적으로 HOMO - LUMO 갭이 큽니다. 그들은 자외선을 흡수하고 모든 가시 광선을 반사하므로 흰색 또는 무색으로 보입니다. 공액 결합은 특히 높은 에너지에서 에너지 수준을 낮춤으로써 분자를 안정화합니다. 켤레 정도가 높을수록 HOMO-LUMO 갭이 작아지고 흡수된 파장이 커집니다. 금속과 대체품도 갭에 영향을 미칩니다.
예를 들어 보겠습니다. 레티놀은 작은 공액 시스템을 가지고 있는 반면 엽록소 a는 질소와 마그네슘이 큰 시스템을 가지고 있습니다. 레티놀은 325nm에서 흡수하는 반면 엽록소 A는 430nm와 662nm에서 모두 흡수합니다. 예상대로 레티놀의 에너지 격차는 더 큽니다.
UV 및 가시광선 또는 UV-Vis 분광 광도계를 사용하여 흡수를 연구할 수 있습니다. 분광 광도계는 샘플이 받는 파장을 제어하는 방법인 광원과 광 검출기로 구성됩니다. 샘플은 일반적으로 투명한 용액입니다. 흡광도는 특정 파장에서 측정하거나 화합물이 종종 두 개 이상의 파장에서 흡수하기 때문에 파장 범위에서 측정할 수 있습니다. 또한, 우리는 분자가 서로 다른 방향과 진동 상태에 있기 때문에 각 전이에 대한 파장 범위를 볼 수 있습니다.
측정하는 동안 빛은 흡수되거나, 분자와 접촉하지 않고 통과하거나, 용매 또는 화합물 분자에서 반사됩니다. 우리는 뒤로 반사되는 소량의 빛을 무시합니다. 때로는 분자에 흡수될 수 있는 빛이 대신 반사됩니다. 우리는 물질이 고유한 몰 감쇠 계수로 특정 파장을 얼마나 잘 전달하는지 설명합니다. 흡광도는 농도에 따라 변하지만 몰 감쇠 계수는 변하지 않습니다.
측정 후 분광 광도계는 투과율이라는 비율로 수신된 빛과 원래 빛을 비교합니다. 흡광도는 투과율의 음의 밑변 10 로그입니다. 분광 광도계에 용매의 흡광도가 있는 경우 이를 빼서 화합물만 표시합니다. 결과는 일반적으로 흡광도 대 파장으로 표시됩니다. 화합물이 가장 많이 흡수하는 파장을 람다 최대라고 합니다. 각 파장에 대한 몰 감쇠 계수를 계산하면 최대 람다에서 가장 높을 것입니다.
몰 감쇠 계수, 흡광도, 시료 농도 및 빛이 시료를 통해 이동한 거리인 경로 길이는 Beer-Lambert 법칙과 관련이 있습니다. 세 가지 변수를 알고 있으면 네 번째 변수를 계산할 수 있습니다.
이 연구실에서는 UV-Vis 분광 광도계를 사용하여 플루오레세인, 베타 카로틴 및 인디고 염료의 흡수 특성을 분석합니다. 그런 다음 Beer-Lambert 법칙을 사용하여 β카로틴 보정 곡선을 만든 다음 β카로틴 용액의 농도를 결정합니다.

염료의 uv-vis 분광법

흡 광도
빛이 물질과 상호 작용할 때 빛의 일부는 흡수되고 나머지는 반사되거나 전달됩니다. 우리가 색을 가진 것으로 인식하는 물질은 가시 범위의 빛을 반사합니다. 우리가 볼 수 있는 물질의 색상은 어떤 빛의 파장이 반사되는지에 따라 다릅니다. 우리가 파란색으로 인식하는 물질은 가시 스펙트럼의 파란색 범위(430 – 480nm)에서 빛을 반사합니다. 색상환에 따르면 동일한 물질이 반사된 빛에 상보적인 빛을 흡수합니다. 따라서 파란색 물질은 가시 스펙트럼의 주황색 영역(590 – 630nm)에서 빛을 흡수합니다. 모든 화합물이 가시 영역에서 흡수되는 것은 아니므로 사람의 눈에는 무색으로 보입니다.
빛은 에너지 E와 파장 λ로 정의됩니다. 여기서 h는 플랑크 상수이고 c는 빛의 속도입니다.
<img src="/CDNSource/lm/labs/70/70_Concepts_1.jpg" alt="에너지 방정식 \(E = \frac{hc}{\lambda}\), 공식, 파장, 광자 에너지 계산" data-altupdatedat="1754907201000">
빛의 파장은 에너지에 반비례합니다. 따라서 더 높은 에너지의 빛은 파장이 더 짧습니다.
<h4>염료</h4>
다른 색깔의 염료는 흡수하는 빛의 파장이 다릅니다. 대부분의 염료는 이중 결합과 단일 결합이 번갈아 가며 결합되는 접합 화합물이며 일반적으로 가시 영역에서 빛을 흡수합니다.
염료 분자의 접합 부분은 매우 짧을 수 있는데, 이는 접합 정도가 낮고 이중 및 단일 결합이 교대로 거의 없음을 의미하거나, 길이가 길다는 것은 많은 이중 및 단일 결합이 교대로 접합 정도가 높다는 것을 의미합니다. 이러한 교대 이중 결합이 반드시 두 탄소 사이에만 있을 필요는 없습니다. 이러한 공액 결합에는 카르보닐기와 탄소와 산소 사이의 이중 결합이 포함될 수 있습니다. 접합 정도는 화합물이 흡수하는 빛의 파장을 결정합니다. 예를 들어, 결합 정도가 높은 화합물은 결합 수준이 낮은 화합물보다 더 긴 파장을 흡수합니다.
분자 궤도 이론에 따르면 비편재화된 전자는 분자 궤도를 차지합니다. 가장 높은 점유 분자 오비탈(HOMO)은 전자가 있는 가장 높은 에너지 오비탈입니다. 가장 낮은 비점유 분자 오비탈(LUMO)은 전자가 없는 가장 낮은 에너지 오비탈입니다. 접합이 거의 또는 전혀 없는 분자는 일반적으로 HOMO와 LUMO 사이에 큰 에너지 갭을 갖습니다. 그러나 공액 분자는 HOMO와 LUMO 사이의 에너지 갭이 더 작습니다.
전자를 낮은 에너지 준위에서 높은 에너지 준위로 또는 HOMO에서 LUMO로 여기시키려면 분자는 두 궤도 사이의 에너지 갭과 동일한 에너지로 빛을 흡수해야 합니다. 이러한 이유로 에너지 갭이 큰 분자는 전자를 여기시키기 위해 UV 광선과 같은 더 높은 에너지의 빛이 필요합니다. 그러나 염료는 에너지 갭이 더 작고 전자를 여기시키기 위해 가시광선과 같은 더 낮은 에너지의 빛이 필요합니다.
<img src="/CDNSource/lm/labs/70/70_Concepts_2.jpg" alt="에너지 갭 방정식 ΔE(HOMO-LUMO) = hc/λ; 분자 분광학, 양자 화학." data-altupdatedat="1754907201000">
이러한 이유로 에너지 갭이 큰 분자는 전자를 여기시키기 위해 UV 광선과 같은 더 높은 에너지의 빛이 필요합니다. 그러나 염료는 에너지 갭이 더 작고 전자를 여기시키기 위해 가시광선과 같은 더 낮은 에너지의 빛이 필요합니다.
빛의 에너지는 파장에 반비례한다는 것을 기억하십시오. 따라서 높은 에너지의 빛은 긴 파장을 가진 낮은 에너지의 빛보다 파장이 짧습니다.
<h4>분광 광도계</h4>
실험적으로 광 흡수도는 UV-Vis(UV-Vis) 분광 광도계를 사용하여 측정합니다. 이 기기는 모노크로메이터에 의해 특정 파장의 빛으로 변환되는 광원을 사용하여 샘플을 통과하고 다른 쪽 끝의 검출기로 들어갑니다. 샘플은 액체에 있어야 하므로 유기 화합물이 고체인 경우 용매가 필요합니다. 이 용액은 큐벳으로 알려진 시료 홀더에 보관됩니다. 샘플에 따라 큐벳은 석영 결정, 유리 또는 플라스틱으로 만들어질 수 있으며 특정 경로 길이를 갖습니다. 이 경로 길이는 빛이 샘플을 통과해야 하는 거리입니다. 용매는 또한 빛을 흡수하기 때문에 용매의 샘플 블랭크가 필요합니다. 따라서 기기가 샘플 화합물의 흡광도 스펙트럼을 캡처할 때 용매의 배경 스펙트럼을 빼서 샘플에 의해 발생한 흡광도만 표시할 수 있습니다. 투과율 T는 샘플을 통과하는 원래 빛의 비율입니다.
<img src="/CDNSource/lm/labs/70/70_Concepts_3.jpg" alt="투과율 방정식 T=P/P₀ 공식, 분광 분석 및 광학 연구의 핵심." data-altupdatedat="1754907201000">
여기서,P0는 샘플에 부딪히기 전의 광선의 방사 조도 또는 단위 면적당 초당 에너지입니다. P는 검출기에 부딪히는 광선의 방사 조도입니다. P는 일반적으로P0보다 낮은데, 이는 빛의 일부가 샘플에 흡수되기 때문입니다.
흡광도 A는 투과율의 음의 로그로 정의됩니다.
<img src="/CDNSource/lm/labs/70/70_Concepts_4.jpg" alt="흡광도 공식: A=log(P₀/P)=-logT; 분광학 분석의 광학 원리." data-altupdatedat="1754907201000">
흡광도의 값 범위는 0(흡수 없음)과 2(99% 흡수) 사이입니다. 빛이 흡수되지 않을 때 P0은 P와 같고 투과율은 1과 같습니다. 따라서 흡광도는 0입니다. 빛의 90%가 흡수되면 10%가 투과되고 T는 0.1과 같습니다. 그 결과 흡광도는 1이 됩니다. 빛의 99%가 흡수되면 1%가 투과되고(T= 0.01) 흡광도는 2와 같습니다.
얻어진 스펙트럼은 파장에 대한 흡광도의 플롯입니다. UV-Vis 분광 광도계의 경우 이 범위는 200 - 800 nm입니다.
<h4>비어-램버트 법칙</h4>
특정 화합물의 투과율 및 흡광도는 용액 내 화합물의 농도와 관련이 있습니다. 이 관계는 Beer-Lambert 법칙에 의해 설명됩니다.
<img src="/CDNSource/lm/labs/70/70_Concepts_5.jpg" alt="Beer-Lambert 법칙 방정식; ᅡ=εcl; 분광학에서의 흡수 다이어그램; 광학 연구." data-altupdatedat="1754907201000">
샘플의 흡광도는 화합물의 농도, 경로 길이 및 몰 감쇠 계수의 곱과 같습니다. 이 계수는 각 화합물에 고유하며 파장에 따라 다릅니다. 그러나 파장이 일정하게 유지되면 몰 감쇠 계수는 농도 변화에 관계없이 동일합니다. λmax로 알려진 샘플의 가장 높은 흡광도에 해당하는 파장은 또한 가장 큰 몰 감쇠 계수를 갖습니다.
<h4>참조</h4>
<ol>
	<li style="font-size:17px">Silberberg, MS (2012). 화학: 물질과 변화의 분자적 성질. 매사추세츠주 보스턴: 맥그로 힐.</li>
	<li style="font-size:17px">Harris, D.C. (2015). 정량적 화학 분석. 뉴욕, 뉴욕 : WH 프리먼 앤 컴퍼니.</li>
</ol>

염료의 UV-Vis 분광법

흡 광도
빛이 물질과 상호 작용할 때 빛의 일부는 흡수되고 나머지는 반사되거나 전달됩니다. ...

Education

교육

JoVE Lab Manual

Chemistry

화학

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

화학 실험실에서 꼭 필요한 기본 커리큘럼 중심 비디오입니다.

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

4분 길이의 강사용 가이드를 통해 염료의 UV-Vis 분광법 수업을 준비하세요. JoVE Lab Manual의 Chemistry 실험을 위한 핵심 준비 단계를 다룹니다.

Chemistry의 염료의 UV-Vis 분광법 강사용 준비 - 8.8K+ 조회수 | JoVE Lab Manual

10분 길이의 학생 프로토콜 영상을 통해 염료의 UV-Vis 분광법 절차를 단계별로 따라 해보세요. JoVE Lab Manual의 Chemistry 컬렉션의 일부입니다.

Chemistry의 염료의 UV-Vis 분광법 학생 프로토콜 - 37K+ 조회수 | JoVE Lab Manual

How Dyes Absorb Visible Light

Description

Transcript

Tags