Name: separating liquids by boiling point
Uploaded: 2020-03-26T07:22:28.000Z
Duration: 3 min 13 s
Channel: JoVE

À medida que um líquido é aquecido, ele ganha energia até que o aumento da desordem da fase gasosa supere as interações intermoleculares na fase líquida. Uma vez que moléculas suficientes estão na fase gasosa, elas escapam do líquido na forma de bolhas. Esse efeito, chamado de ebulição, ocorre quando a pressão total de vapor da substância é igual à pressão atmosférica.
A pressão de vapor é a pressão do vapor em equilíbrio com sua fase condensada e varia com a temperatura. Em uma mistura de líquidos, cada componente tem sua própria pressão de vapor, que chamamos de pressão parcial. A pressão total de vapor da mistura é igual à soma das pressões parciais. Se os líquidos são miscíveis, o que significa que eles sempre formam uma solução homogênea, a pressão parcial de cada componente é a pressão de vapor do composto puro nessa temperatura vezes sua fração molar no líquido.
A temperatura na qual a primeira bolha de vapor começa a se formar em uma mistura líquida é chamada de ponto de bolha. Para um líquido puro, tanto o ponto de bolha quanto a temperatura na qual o vapor começa a condensar, ou o ponto de orvalho, são iguais ao ponto de ebulição. No entanto, para uma mistura de dois líquidos miscíveis, tanto o ponto de bolha quanto o ponto de orvalho estarão entre os pontos de ebulição dos componentes.
Quando a mistura ferve pela primeira vez, o vapor é rico com o composto com o ponto de ebulição mais baixo ou o composto mais volátil. Isso aumenta a proporção do composto com o ponto de ebulição mais alto, ou o composto menos volátil, na mistura líquida.
A destilação é uma técnica de separação que aproveita esse fenômeno. Em uma destilação simples, uma mistura líquida homogênea é fervida. O vapor ascendente entra então na câmara interna de um condensador resfriado a água. O vapor se condensa em um líquido, chamado destilado, que é então coletado em um recipiente separado.
À medida que a ebulição continua, as composições do líquido e do vapor mudam à medida que o componente mais volátil é removido. Então, se coletarmos o destilado em pequenas frações, veremos que cada fração contém os compostos em uma proporção molar diferente.
À medida que a proporção do componente menos volátil na mistura líquida aumenta, o mesmo acontece com o ponto de bolha e o ponto de orvalho. Plotar os pontos de bolha e orvalho da mistura versus as frações molares dos componentes cria um diagrama de ponto de ebulição. Uma vez que tenhamos este diagrama, podemos usar a curva do ponto de orvalho para determinar a composição do vapor a uma determinada temperatura.
Neste laboratório, você configurará e executará a destilação simples de uma mistura de ciclohexano e tolueno e registrará a temperatura do vapor durante todo o experimento. Em seguida, você usará o diagrama de ponto de ebulição publicado para ciclohexano e tolueno para determinar a composição do vapor, permitindo estimar a composição da mistura líquida durante a destilação.

destilação simples

Simple Distillation

<h4>Destilação de uma mistura miscível</h4>
Alguns líquidos evaporam totalmente com o tempo se deixados em um recipiente aberto em temperatura ambiente. No entanto, esse processo de evaporação pode ser significativamente acelerado se o líquido for aquecido. À medida que o líquido é aquecido, as moléculas dentro dele ganham energia para escapar da fase líquida e fazer a transição para a fase gasosa na forma de bolhas. Esse fenômeno é chamado de ebulição.
<h4>Pressão de vapor</h4>
Considere um recipiente fechado de líquido. Inicialmente, parte desse líquido evapora, mas apenas até que a taxa de vaporização seja igual à taxa de condensação. Depois que esse ponto é alcançado, não há mais mudanças no sistema e o líquido e o vapor estão em equilíbrio. Uma vez estabelecido, a pressão exercida pelo vapor acima do líquido é chamada de pressão de vapor. A tendência de um líquido vaporizar é chamada de volatilidade. Um líquido mais volátil tem uma pressão de vapor mais alta, enquanto um líquido menos volátil tem uma pressão de vapor mais baixa.
Quando um recipiente aberto de líquido é aquecido, mais líquido evapora. Se calor suficiente for adicionado, bolhas de vapor se formam no líquido e o líquido ferve. A temperatura na qual a pressão de vapor do líquido é igual à pressão atmosférica é conhecida como ponto de ebulição.
Para uma substância pura, a pressão de vapor é simples de determinar. Que tal uma mistura de diferentes líquidos? Se os líquidos puros formarem uma solução homogênea miscível, cada um contribuirá para a pressão total do vapor como pressões parciais. A pressão total do gás de uma mistura de gases é igual à soma das pressões individuais que cada gás exerceria isoladamente. Esta regra é conhecida como lei de Dalton. Portanto, para determinar a pressão de vapor total da mistura, você deve conhecer as pressões de vapor das substâncias puras e a contribuição molar de cada líquido para a mistura total, um valor conhecido como fração molar. Essa relação é conhecida como lei de Raoult:
pA = pA* xA
onde pA é a pressão de vapor de um componente líquido em uma mistura, pA* é a pressão de vapor do líquido puro isoladamente, que pode ser referenciada na literatura, e xA é a fração molar do componente líquido na mistura líquida. As frações molares são calculadas dividindo o número de moles do componente líquido pelo número total de moles de cada componente na mistura líquida.
A lei de Dalton das pressões parciais pode ser aplicada uma vez que você conheça a pressão de vapor de cada componente individual.
P = pA + pB
A pressão total (P) é a soma da pressão de vapor de ambos os líquidos acima da mistura, onde pA e pB são as pressões de vapor dos líquidos A e B, respectivamente, acima da mistura.
<h4>ponto de ebulição</h4>
A temperatura na qual uma substância orgânica pura é alterada da fase líquida para a fase gasosa é conhecida como ponto de ebulição. Em uma mistura de líquidos miscíveis, a solução ferve quando a pressão total de vapor da solução é igual à pressão atmosférica. Assim, o ponto de ebulição de uma mistura ocorre a uma temperatura entre os pontos de ebulição dos dois líquidos puros.
À medida que a mistura é aquecida até o ponto de ebulição, algumas das moléculas escapam da fase líquida e entram na fase gasosa. A temperatura na qual as primeiras bolhas começam a se formar em uma solução miscível que está sendo aquecida é a temperatura do ponto de bolha. No caso de um líquido puro, o ponto de bolha é o mesmo que o ponto de ebulição.
A fase gasosa é rica em moléculas do componente mais volátil, ou o componente com maior pressão de vapor e menor ponto de ebulição. O número de moléculas que evaporam aumenta à medida que mais calor é aplicado. Assim, a fase líquida é rica em moléculas do componente menos volátil, ou o componente com menor pressão de vapor e maior ponto de ebulição. A temperatura na qual as primeiras gotas de líquido começam a se formar durante a destilação é conhecida como temperatura do ponto de orvalho.
<h4>Diagrama de Equilíbrio Vapor-Líquido</h4>
Um diagrama de equilíbrio vapor-líquido é um gráfico da temperatura de equilíbrio da fração molar dos componentes de uma mistura binária, com uma curva desenhada para a fase líquida e a fase de vapor. O eixo x representa a fração molar de cada um dos dois componentes da mistura e o eixo y é a temperatura. Esses gráficos estão disponíveis na literatura para misturas comuns e podem ser usados para identificar as temperaturas do ponto de ebulição de uma mistura, dada a fração molar de cada componente. Eles também são usados para determinar a composição de cada fase em um experimento de destilação.
<h4>destilação </h4>
A destilação é uma técnica de separação que aproveita as propriedades do ponto de ebulição das misturas. Para efectuar a destilação, aquece-se uma mistura miscível de dois líquidos com uma diferença significativa nos pontos de ebulição — pelo menos 20 °C — À medida que a solução aquece e atinge o ponto de bolha do componente mais volátil, algumas moléculas do componente mais volátil fazem a transição para a fase gasosa e viajam para cima no condensador. O condensador é um tubo de vidro com seções internas e externas separadas. O vapor viaja para a seção interna do condensador, onde é condensado em líquido pela água fria que flui na seção externa do condensador. Esse vapor condensado é chamado de destilado e é coletado em um cilindro graduado ou tubo de ensaio.
À medida que a destilação progride, a temperatura necessária para ferver a solução aumenta à medida que o componente mais volátil ferve mais cedo. Assim, a composição do destilado muda com o tempo. No início da destilação, o destilado é rico com o componente mais volátil; No meio da destilação, o destilado contém uma mistura dos dois componentes; e no final da destilação, o destilado é rico com o componente menos volátil.
O diagrama de equilíbrio vapor-líquido mostra a mudança na composição do líquido no frasco e do destilado ao longo da destilação. Existem duas curvas no gráfico; A curva inferior descreve o ponto de ebulição do líquido no frasco no que se refere à sua composição, enquanto a curva superior descreve a temperatura do vapor no que se refere à sua composição. Por extensão, a curva superior descreve a composição do destilado.
Um diagrama de equilíbrio vapor-líquido publicado na literatura pode ser usado para identificar a composição do líquido e do vapor a uma determinada temperatura durante o experimento. Isso pode ajudar a determinar quando terminar a destilação para separar os dois componentes.
<h4>Referências</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Química e Reatividade Química. Belmont, CA: Brooks / Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silderberg, M.S. (2009). Química: A Natureza Molecular da Matéria e da Mudança. Boston, MA: Colina McGraw.</li>
	<li style="font-size:17px">Felder, R.M., Rousseau, R.W. (2000). Princípios Elementares de Processos Químicos. Nova York, NY: Wiley and Sons, Inc.</li>
</ol>

Destilação Simples

Destilação de uma mistura miscível
Alguns líquidos evaporam totalmente com o tempo se deixados em um recipiente aberto em temperatura ambiente. No entanto, isso ...

Education

JoVE Lab Manual

Chemistry

Química

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. A more volatile liquid has a higher vapor pressure, while a less volatile liquid has a lower vapor pressure. When an open container is heated, the liquid boils at the temperature where its vapor pressure matches atmospheric pressure.

For a mixture of miscible liquids, each component contributes to the total vapor pressure as a partial pressure. Dalton’s law says the total pressure is the sum of the individual pressures, and Raoult’s law links each component’s vapor pressure to its pure vapor pressure and mole fraction. The mole fraction is the number of moles of one liquid divided by the total moles in the mixture. For two liquids, the total vapor pressure is the sum of the partial pressures of both components.

A mixture boils at a temperature between the boiling points of the two pure liquids. The first bubbles that form define the bubble point temperature. In a pure liquid, the bubble point and boiling point are the same. During heating, the vapor becomes richer in the more volatile component, while the liquid left behind becomes richer in the less volatile component. The first drops of liquid that form during distillation occur at the dew point temperature.

Vapor-liquid equilibrium diagrams help track these changes. These plots show temperature against mole fraction for a binary mixture, with one curve for the liquid phase and one for the vapor phase. They are available in the literature for common mixtures and can be used to estimate boiling temperatures and phase composition at a given mole fraction. They also help show how the liquid in the flask and the distillate change during the experiment.

In distillation, a miscible mixture with a significant boiling point difference, usually at least 20 °C, is heated. As the more volatile component reaches its bubble point, vapor rises into a condenser. The condenser has inner and outer sections, and cold water in the outer section cools the vapor back into liquid. This liquid is the distillate, and it is collected in a graduated cylinder or test tube.

Separating Liquids by Boiling Point

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 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

Vídeos abrangentes e focados no currículo para instrutores e alunos de cursos introdutórios de laboratório de química

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

Learn how distillation separates miscible liquids using vapor pressure, Raoult’s law, and condensation in a condenser as boiling point changes over time.

Separating Liquids by Boiling Point | JoVE K12

Prepare-se para ensinar Destilação Simples com este guia do instrutor de 3 minutos. Abrange as principais etapas de preparação para o laboratório Chemistry no JoVE Lab Manual.

Preparação do Instrutor para Destilação Simples em Chemistry - 8.7K+ visualizações | JoVE Lab Manual

Siga os procedimentos passo a passo de Destilação Simples neste vídeo de protocolo estudantil de 7 minutos. Parte da coleção Chemistry no JoVE Lab Manual.

Protocolo do Estudante para Destilação Simples em Chemistry - 57K+ visualizações | JoVE Lab Manual

Separating Liquids by Boiling Point

Description

Transcript

Tags