Name: absorbance spectra and beer-lambert analysis
Uploaded: 2020-03-26T07:22:26.000Z
Duration: 2 min 53 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

Beer's Law

많은 화학 반응은 정방향과 역방향의 두 방향으로 진행됩니다. 시간이 지남에 따라 정방향 및 역방향 반응이 동일한 비율로 발생하고 반응물과 생성물의 농도는 더 이상 변하지 않습니다. 이것을 화학적 평형이라고 합니다.
화학적 평형에서 각 성분의 농도는 평형 상수 K에 의해 서로 관련되며, 이는 반응물 농도에 대한 생성물 농도의 비율이며, 각각은 화학량론 계수의 거듭제곱으로 상승합니다.
하지만 평형 농도는 어떻게 결정할까요? 한 가지 방법은 제품이 샘플을 통과하기 전과 후에 흡수하는 빛의 파장의 강도를 측정합니다. 강도 차이를 흡광도라고 하며, 이는 시료에 포함된 흡수 화합물의 양에 해당합니다.
전자가 대부분 바닥 상태를 차지한다는 것을 기억할 것입니다. 일정량의 에너지를 흡수하면 더 높은 에너지 수준으로 흥분합니다. 그 에너지는 빛의 특정 파장에 해당합니다. 이 파장을 찾고 분광 광도계로 흡광도를 측정할 수 있으며, 이 분광광도계는 샘플을 통해 광선을 유도하고 하나 이상의 파장에서 강도 변화를 측정합니다.
흡광도는 입사광의 강도에 대한 감쇠된 빛의 강도의 음의 로그와 같습니다. 서로 다른 알려진 제품 농도를 가진 여러 용액의 흡광도 값을 표시함으로써 흡광도와 농도 사이의 선형 관계를 관찰합니다. 이것은 맥주의 법칙의 예입니다.
맥주의 법칙은 이 방정식으로 수학적으로 표현되며, 여기서 A는 흡광도, 엡실론은 몰 감쇠 계수, 각 화합물에 대해 변하는 상수, l은 샘플을 통과하는 빛의 경로 길이, c는 화합물의 농도입니다.
특정 파장 및 경로 길이에서 주어진 화합물에 대한 선형 함수를 식별함으로써 평형 상태에서 용액의 흡광도 데이터를 사용하여 생성물의 평형 농도를 결정할 수 있습니다. 거기에서 반응물의 평형 농도를 계산하고 평형 상수를 풀 수 있습니다. 이 실험실에서는 철 (III) 이소 티오 시아네이트 용액을 준비하고 분광 광도계를 사용하여 다양한 농도에서 흡광도를 측정합니다.

맥주의 법칙

흡광도와 형광
빛이 물질에 부딪히면 흡수, 전달 또는 반사됩니다. 일반적으로 물질은 다양한 파장의 빛과 상호 작용하며, 각 파장은 분자 또는 원자와 다르게 상호 작용합니다. 물질은 특정 범위의 파장을 흡수하고, 다른 범위의 파장을 반사하고, 다른 파장의 빛을 투과할 수 있습니다.
분자가 빛을 흡수할 때, 에너지는 네 가지 다른 방식으로 사용됩니다: (1) 분자가 분자 속도를 변화시키는 번역; (2) 분자 사이의 거리가 빠르게 변하는 진동; (3) 원자가 분자의 결합 주위를 회전하게 하는 회전; (4) 전자가 더 높은 에너지 수준으로 전환되도록 하는 전자 여기.
<h4>에너지 수준</h4>
1913년, 닐스 보어(Niels Bohr)는 수소 원자에 대한 모델을 제안했는데, 이 모델에서는 전자가 정지 상태(stationary state)라고 불리는 고정된 원형 궤도를 그리며 핵 주위를 이동했습니다. 각 궤도 또는 정지 상태와 관련된 에너지는 고정된 개별 에너지에서만 존재합니다. 전자가 다른 궤도로 이동할 때만 에너지가 흡수되거나 방출됩니다. 전자는 결코 그 사이에 있지 않습니다. 이 변화는 흡수 또는 방출된 에너지가 두 에너지 상태 간의 차이와 같은 경우에만 발생합니다.
보어의 모델에서 양자 수 n은 전자의 에너지를 나타냅니다. 전자가 가능한 가장 낮은 에너지 상태를 차지할 때 n = 1인 바닥 상태를 차지한다고 합니다. 전자가 에너지가 첫 번째 상태와 두 번째 상태의 차이와 같은 광자를 흡수하면 전자는 여기가 되고 기저 상태에서 여기 상태(n = 2)로 전환됩니다. 광자의 에너지가 첫 번째 상태와 세 번째 상태의 차이와 같으면 전자는 세 번째 상태 또는 n = 3 등으로 전이됩니다.
전자는 자발적으로 바닥 상태 또는 다른 더 낮은 여기 상태로 돌아갈 수 있습니다. 이런 일이 발생하면 여기(excitation)에서 얻은 초과 에너지가 방출된 광자의 형태로 방출됩니다. 광자의 에너지는 두 에너지 상태 간의 차이와 같으며 서로 다른 빛의 파장에 해당합니다.
<h4>흡수 및 방출 스펙트럼</h4>
대부분의 물질은 한 파장에서 최대한의 빛을 흡수하거나 방출하지만 다양한 파장의 빛을 흡수하거나 방출하는 경향이 있습니다. 이러한 파장 범위를 스펙트럼이라고 합니다. 흡수된 빛의 에너지는 흡수 스펙트럼을 사용하여 정량화되고 시각화되며, 방출된 빛의 에너지는 방출 스펙트럼을 사용하여 정량화되고 시각화됩니다.
흡수 및 방출 스펙트럼은 분광 광도계를 사용하여 측정되며, 이는 샘플을 통해 빛을 투과한 다음 이를 통과하는 빛의 파장과 강도를 모두 측정하는 장치입니다. 분광 광도계 내부에는 회절 격자 또는 프리즘이 있으며, 이는 들어오는 빛을 구성 파장으로 분리합니다. 그런 다음 서로 다른 파장이 샘플을 통해 전송되고 강도는 선형 전하 결합 장치(CCD) 검출기에 기록됩니다. CCD는 픽셀이라고 하는 빛에 민감한 요소를 형성하는 실리콘 표면에 에칭된 집적 회로입니다. CCD는 회절된 빛을 수집 및 분류하고 흡수 파장에서 다시 읽습니다.
샘플의 흡광도를 측정할 때 용질은 일반적으로 용매에 용해되어 큐벳으로 알려진 용기에 배치됩니다. 그런 다음 샘플을 분광 광도계 내부에 놓고 투과광의 강도를 빛의 파장과 함께 측정하여 흡광도 스펙트럼을 얻습니다. 예상대로 투과광의 강도는 분광 광도계 내부에 샘플이 없을 때보다 낮습니다.
이는 투과광이 샘플, 큐벳 및 용매에 흡수되기 때문입니다. 샘플을 측정하기 전에 분광 광도계를 '블랭크'로 보정해야 합니다. 블랭크는 용질을 용해하는 데 사용되는 용매만 들어 있는 큐벳입니다. 분광 광도계는 큐벳과 용매로 인한 총 흡광도가 샘플의 측정된 흡광도에서 차감되도록 보정됩니다. 이를 통해 관심 종에만 기인하는 흡광도를 기록할 수 있습니다.
흡광도는 종종 최대 흡광도 파장인 하나의 파장에서 측정됩니다. 그러나 흡수 스펙트럼을 획득하기 위해 다양한 파장에서 흡수를 측정할 수도 있습니다. 이를 위해 샘플은 다양한 파장의 입사광에 노출되고 각 파장에서 흡수가 기록됩니다. 샘플이 빛을 방출하는 경우, 입사 파장이 최대 흡광도의 파장으로 고정된다는 점을 제외하고는 방출 스펙트럼도 유사하게 측정됩니다. 그런 다음 기기는 다양한 파장에서 방출되는 빛의 강도를 측정합니다.
<h4>비어-램버트 법칙</h4>
최대 흡광도의 파장에서 샘플의 흡광도는 샘플에 대한 정보, 즉 농도를 제공합니다. Beer-Lambert 법칙은 투과율과 시료 농도를 관련시키는 방정식입니다. 투과율 또는 투과광의 강도는 샘플을 통과하는 원래 빛의 비율 I를 입사광의 강도 I0으로 나눈 값입니다.
<img src="/CDNSource/lm/labs/49/49_Concepts_1.jpg" alt="투과율 방정식 \(T = \frac{I}{I_0}\), 광학 밀도 분석을 위한 다이어그램." data-altupdatedat="1754907201000">
Beer-Lambert 법칙에 따르면 용액에 있는 종의 광학 흡광도 A는 투과율의 음의 로그와 관련이 있습니다.
<img src="/CDNSource/lm/labs/49/49_Concepts_2.jpg" alt="흡광도 공식 A=-log(T), 분광학 연구에서 광학 흡수 분석을 위한 방정식." data-altupdatedat="1754907201000">
Beer-Lambert 법칙의 다른 버전에서는 용액에 있는 종의 광학 흡광도 A가 파장 λ와 경로 길이 l이 일정하게 유지될 때 해당 종의 농도 c에 선형적으로 비례한다고 말합니다.
<img src="/CDNSource/lm/labs/49/49_Concepts_3.jpg" alt="Beer-Lambert 법칙 방정식, A=εcl, 흡수 개념, 분광 데이터 분석, 물리 다이어그램." data-altupdatedat="1754907201000">
몰 감쇠 계수(ε)는 한 종이 주어진 파장에서 빛을 얼마나 강하게 흡수하는지를 측정한 것입니다. 몰 감쇠 계수가 클수록 흡광도가 커집니다. 경로 길이 l은 빛이 샘플을 통해 이동하는 거리이며, 이는 큐벳의 너비입니다. 표준 큐벳의 경로 길이는 1cm입니다.
흡광도와 농도 사이의 이러한 선형 관계는 흡광도를 기반으로 미지 시료의 농도를 결정하는 데 사용되는 강력한 도구입니다. 이를 위해 알려진 용질 농도의 구배를 사용하여 표준 곡선을 생성합니다. 피크 흡광도 파장 λmax에서의 흡광도는 각 농도에 대해 측정됩니다.
농도 대 흡광도를 플로팅하면 Beer-Lambert 방정식에 해당하는 선형 관계가 관찰됩니다. 이 선의 기울기는 경로 길이와 몰 감쇠 계수의 곱과 같습니다. 이 계산된 선형 함수를 사용하여 미지 시료의 흡광도를 알고 있는 경우 농도를 쉽게 측정할 수 있습니다.
분석 중인 샘플이 평형 상태의 반응인 경우, 흡광도가 해당 생성물 또는 반응물에 특이적인 λmax에서 측정되는 경우 Beer의 법칙을 사용하여 생성물 또는 반응물의 평형 농도를 결정할 수 있습니다. 농도가 알려지면 나머지 반응물과 생성물의 평형 농도를 결정한 다음 평형 상수 Keq를 풀 수 있습니다.
<h4>참조</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). 화학 및 화학 반응성. 캘리포니아 벨몬트 : Brooks / Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). 화학: 물질과 변화의 분자적 성질. 매사추세츠주 보스턴: 보스턴 맥그로 힐.</li>
	<li style="font-size:17px">Harris, D.C. (2015). 정량적 화학 분석. 뉴욕, 뉴욕 : WH 프리먼 앤 컴퍼니.</li>
</ol>

흡광도와 형광
빛이 물질에 부딪히면 흡수, 전달 또는 반사됩니다. 일반적으로 물질은 범위와 상호 작용합니다 ...

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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 moves an electron to a higher energy level. In Niels Bohr’s model, electrons in the hydrogen atom move in fixed circular orbits called stationary states, and each state has a discrete energy. An electron can move only when it absorbs or emits energy equal to the difference between two states.

The lowest energy state is the ground state, or n = 1. If a photon has the right energy, the electron can move to a higher state such as n = 2 or n = 3. When the electron returns to a lower state, it releases the extra energy as an emitted photon. The photon energy matches the energy gap between the two states and corresponds to specific wavelengths of light.

Most substances absorb or emit most strongly at one wavelength, but they usually interact with a range of wavelengths. That range is called a spectrum. An absorption spectrum shows how much light a sample absorbs at different wavelengths, and an emission spectrum shows the light a sample gives off. These spectra are measured with a spectrophotometer, which sends light through a sample and records the wavelength and intensity of the light that passes through.

Inside the spectrophotometer, a diffraction grating or a prism separates incoming light into its component wavelengths. The light then passes through the sample, and a linear charge-coupled device, or CCD, detector records the intensity. A CCD is an integrated circuit on silicon that contains light-sensitive pixels. It collects and sorts the diffracted light and reads it back at an absorption wavelength.

For absorbance measurements, the solute is usually dissolved in a solvent and placed in a cuvette, which is the container used in the instrument. The sample is then placed in the spectrophotometer, and the intensity of transmitted light is measured along with wavelength to produce an absorbance spectrum. The transmitted light is lower than when no sample is present because light is absorbed by the sample, the cuvette, and the solvent. Before samples are measured, the spectrophotometer is calibrated with a blank, which is a cuvette that contains only the solvent. This step removes the absorbance from the cuvette and solvent so the reading reflects only the species of interest.

Absorbance is often measured at the wavelength of maximum absorbance, but it can also be recorded across a range of wavelengths. For emission spectra, the incident wavelength is fixed at the wavelength of maximum absorbance, and the instrument measures emitted light over a range of wavelengths. The Beer-Lambert Law then connects absorbance to sample concentration. Transmittance is the fraction of light that passes through the sample, I divided by I0, and absorbance is related to the negative log of transmittance.

A second form of the Beer-Lambert Law shows that absorbance is directly proportional to concentration when wavelength and pathlength stay constant. The molar attenuation coefficient, ε, describes how strongly a species absorbs light at a given wavelength. The pathlength, l, is the distance the light travels through the sample, which is the width of the cuvette. Standard cuvettes have a 1 cm pathlength. This linear relationship makes it possible to find the concentration of an unknown sample from its absorbance.

To do that, a standard curve is made with known concentrations of the solute. The absorbance at λ max is measured for each standard, and the results are plotted as concentration versus absorbance. The line that appears matches the Beer-Lambert equation, and its slope equals the product of the pathlength and the molar attenuation coefficient. Once that line is known, the concentration of an unknown sample can be calculated from its absorbance.

Beer’s Law can also be used for reactions at equilibrium. If absorbance is measured at the λ max of a specific product or reactant, the equilibrium concentration of that species can be found. The concentrations of the other reactants and products can then be determined, and the equilibrium constant K eq can be solved.

Absorbance Spectra and Beer-Lambert Analysis

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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 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

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...

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

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Explore how spectrophotometers measure absorbance spectra, how blank calibration works, and how Beer-Lambert Law is used to find concentration and equilibrium values.

Absorbance Spectra and Beer-Lambert Analysis | JoVE K12

Louisiana Student Standards for Science

motion-and-stability-forces-and-interactions

Motion And Stability: Forces And Interactions

HS-PS2-6

7분 길이의 강사용 가이드를 통해 맥주의 법칙 수업을 준비하세요. JoVE Lab Manual의 Chemistry 실험을 위한 핵심 준비 단계를 다룹니다.

Chemistry의 맥주의 법칙 강사용 준비 - 4.7K+ 조회수 | JoVE Lab Manual

17분 길이의 학생 프로토콜 영상을 통해 맥주의 법칙 절차를 단계별로 따라 해보세요. JoVE Lab Manual의 Chemistry 컬렉션의 일부입니다.

Chemistry의 맥주의 법칙 학생 프로토콜 - 40K+ 조회수 | JoVE Lab Manual

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Ions and Ionic Charges

In ordinary chemical reactions, the nucleus &mdash; which contains the protons and neutrons of each atom and thus identifies the element &mdash; remains ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

bond-polarity-dipole-moment-and-percent-ionic-character

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

Model basic atomic structure and relate an element's atomic structure to its bonding, reactivity, and placement on the Periodic Table.

IPC.7.A

physical-and-chemical-properties-of-matter

Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

Use patterns within the Periodic Table to predict the relative physical and chemical properties of elements.

IPC.7.B

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

phase-transitions-vaporization-and-condensation

Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

Explain how physical and chemical properties of substances are related to their usage in everyday life such as in sunscreen, cookware, industrial applications, and fuels.

IPC.7.C

Science concepts. The student knows that relationships exist between the structure and properties of matter. The student is expected to:

Absorbance Spectra and Beer-Lambert Analysis

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