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

액체가 가열되면 기체 상태의 증가된 무질서가 액체 상태의 분자간 상호 작용보다 클 때까지 에너지를 얻습니다. 충분한 분자가 기체 상태에 있으면 거품 형태로 액체를 빠져나갑니다. 끓는점이라고하는이 효과는 물질의 총 증기압이 대기압과 같을 때 발생합니다.
증기압은 응축된 위상과 평형 상태에 있는 증기의 압력이며 온도에 따라 변합니다. 액체의 혼합물에서 각 구성 요소에는 자체 증기압이 있으며, 이를 분압이라고 합니다. 혼합물의 총 증기압은 분압의 합과 같습니다. 액체가 혼화성이 있는 경우, 즉 항상 균일한 용액을 형성하는 경우 각 구성 요소의 분압은 해당 온도에서 순수한 화합물의 증기압에 액체의 몰 분율을 곱한 값입니다.
액체 혼합물에서 증기의 첫 번째 기포가 형성되기 시작하는 온도를 기포 점이라고 합니다. 순수한 액체의 경우 기포점과 증기가 응축되기 시작하는 온도 또는 이슬점은 모두 끓는점과 같습니다. 그러나 두 가지 혼합성 액체의 혼합물의 경우 기포점과 이슬점은 모두 구성 요소의 끓는점 사이에 있습니다.
혼합물이 처음 끓을 때 증기는 끓는점이 낮은 화합물 또는 휘발성이 더 높은 화합물로 풍부합니다. 이것은 액체 혼합물에서 끓는점이 더 높거나 휘발성이 적은 화합물의 비율을 증가시킵니다.
증류는 이러한 현상을 이용하는 분리 기술입니다. 간단한 증류에서는 균질한 액체 혼합물을 끓입니다. 그런 다음 상승하는 증기는 수냉식 응축기의 내부 챔버로 들어갑니다. 증기는 증류액이라고 하는 액체로 응축된 다음 별도의 용기에 수집됩니다.
끓는 것이 계속됨에 따라 더 휘발성 성분이 제거됨에 따라 액체와 증기의 조성이 변합니다. 따라서 증류 액을 작은 분획으로 수집하면 각 분획에 다른 몰 비율의 화합물이 포함되어 있음을 알 수 있습니다.
액체 혼합물에서 휘발성이 적은 성분의 비율이 증가함에 따라 기포점과 이슬점도 증가합니다. 혼합물의 거품 및 이슬점과 성분의 몰 분율을 비교하면 끓는점 다이어그램이 만들어집니다. 이 다이어그램이 있으면 이슬점 곡선을 사용하여 주어진 온도에서 증기의 구성을 결정할 수 있습니다.
이 실험실에서는 시클로헥산과 톨루엔 혼합물의 간단한 증류를 설정 및 수행하고 실험 전반에 걸쳐 증기의 온도를 기록합니다. 그런 다음 시클로헥산과 톨루엔에 대해 발표된 끓는점 다이어그램을 사용하여 증기의 조성을 결정하고 증류 전반에 걸쳐 액체 혼합물의 조성을 추정할 수 있습니다.

간단한 증류

Simple Distillation

<h4>혼합성 혼합물의 증류</h4>
일부 액체는 실온의 열린 용기에 그대로 두면 시간이 지남에 따라 완전히 증발합니다. 그러나 이 증발 과정은 액체가 가열되면 크게 가속화될 수 있습니다. 액체가 가열됨에 따라 그 안의 분자는 액체 상태를 탈출하고 거품 형태로 기체 상태로 전이할 수 있는 에너지를 얻습니다. 이러한 현상을 비등(boiling)이라고 합니다.
<h4>증기압</h4>
밀폐된 액체 용기를 고려하십시오. 처음에는 이 액체의 일부가 증발하지만 기화 속도가 응축 속도와 같아질 때까지만 증발합니다. 이 지점에 도달한 후에는 시스템에 더 이상의 변화가 없으며 액체와 증기가 평형 상태에 있습니다. 이것이 확립되면 액체 위의 증기에 의해 가해지는 압력을 증기압이라고 합니다. 액체가 기화하는 경향을 휘발성이라고 합니다. 휘발성이 높은 액체는 증기압이 더 높고 휘발성이 낮은 액체는 증기압이 낮습니다.
열린 액체 용기를 가열하면 더 많은 액체가 증발합니다. 충분한 열이 가해지면 액체에 증기 거품이 형성되고 액체가 끓습니다. 액체의 증기압이 대기압과 같은 온도를 끓는점이라고 합니다.
순수한 물질의 경우 증기압을 간단하게 결정할 수 있습니다. 다른 액체의 혼합물은 어떻습니까? 순수한 액체가 혼화성 균질한 용액을 형성하는 경우, 각 액체는 분압으로 총 증기압에 기여합니다. 가스 혼합물의 총 가스 압력은 각 가스가 단독으로 가하는 개별 압력의 합과 같습니다. 이 규칙을 Dalton의 법칙이라고 합니다. 따라서 혼합물의 총 증기압을 결정하려면 순수 물질의 증기압과 총 혼합물에 대한 각 액체의 몰 기여도(몰 분율로 알려진 값)를 알아야 합니다. 이 관계는 라울트의 법칙으로 알려져 있습니다.
pA = pA* xA
여기서p A는 혼합물 내 액체 성분의 증기압이고, pA*는 문헌에서 참조할 수 있는 격리된 순수한 액체의 증기압이며, xA는 액체 혼합물 내 액체 성분의 몰 분율입니다. 몰 분율은 액체 혼합물에 있는 각 성분의 총 몰 수에 대해 액체 성분의 몰 수를 나누어 계산합니다.
Dalton의 부분 압력 법칙은 각 개별 구성 요소의 증기압을 알고 있으면 적용할 수 있습니다.
P = pA + pB
총 압력(P)은 혼합물 위의 두 액체의 증기압의 합이며, 여기서 pA 및p B는 각각 혼합물 위의 액체 A 및 B의 증기압입니다.
<h4>끓는점</h4>
순수한 유기 물질이 액체 상태에서 기체 상태로 변하는 온도를 끓는점이라고 합니다. 혼합성 액체의 혼합물에서 용액의 총 증기압이 대기압과 같을 때 용액이 끓습니다. 따라서 혼합물의 끓는점은 두 개의 순수한 액체의 끓는점 사이의 온도에서 발생합니다.
혼합물이 끓는점까지 가열되면 일부 분자는 액체 상태를 벗어나 기체 상태로 들어갑니다. 가열되는 혼화성 용액에서 첫 번째 기포가 형성되기 시작하는 온도가 기포점 온도입니다. 순수한 액체의 경우 기포점은 끓는점과 같습니다.
기체 상태는 휘발성이 더 높은 성분 또는 증기압이 높고 끓는점이 낮은 성분의 분자가 풍부합니다. 증발하는 분자의 수는 더 많은 열이 가해질수록 증가합니다. 따라서, 액상은 휘발성이 적은 성분 또는 증기압이 낮고 끓는점이 높은 성분의 분자가 풍부합니다. 증류 중에 첫 번째 액체 방울이 형성되기 시작하는 온도를 이슬점 온도라고 합니다.
<h4>증기-액체 평형 다이어그램</h4>
증기-액체 평형 다이어그램은 이진 혼합물 성분의 몰 분율의 평형 온도에 대한 플롯으로, 액체 위상과 증기 위상에 대해 그려진 곡선이 있습니다. x축은 혼합물에 있는 두 성분 각각의 몰 분율을 나타내고 y축은 온도입니다. 이러한 플롯은 일반적인 혼합물에 대한 문헌에서 사용할 수 있으며 각 성분의 몰 분율이 주어지면 혼합물의 끓는점 온도를 식별하는 데 사용할 수 있습니다. 또한 증류 실험에서 각 단계의 구성을 결정하는 데 사용됩니다.
<h4>증류법 </h4>
증류는 혼합물의 끓는점 특성을 이용하는 분리 기술입니다. 증류법을 실행하기 위하여는, 비등점에 있는 뜻깊은 다름을 가진 2개의 액체의 혼화성 혼합물 — 적어도 20 °C — 가열된다. 용액이 가열되어 휘발성이 더 높은 성분의 기포 점에 도달하면 휘발성이 더 높은 성분의 일부 분자가 기체 상태로 전환되어 응축기로 위쪽으로 이동합니다. 콘덴서는 내부 및 외부 섹션이 분리된 유리관입니다. 증기는 응축기의 내부 부분으로 이동하여 응축기의 외부 부분으로 흐르는 냉수에 의해 액체로 응축됩니다. 이 응축된 증기를 증류액이라고 하며 눈금이 매겨진 실린더 또는 시험관에 수집됩니다.
증류가 진행됨에 따라 휘발성이 더 높은 성분이 더 일찍 끓어남에 따라 용액을 끓이는 데 필요한 온도가 증가합니다. 따라서 증류 액의 조성은 시간이 지남에 따라 변합니다. 증류법 초기에, 증류액은 휘발성이 더 강한 성분으로 부유합니다. 증류의 중간에, 증류 액은 두 가지 성분의 혼합물을 포함합니다. 그리고 증류가 끝나면 증류액은 휘발성이 적은 성분이 풍부합니다.
증기 액체 평형 다이어그램은 증류 과정에서 플라스크와 증류 액의 액체 조성 모두에서 변화를 보여줍니다. 플롯에는 두 개의 곡선이 있습니다. 하단 곡선은 플라스크에 있는 액체의 끓는점을 그 조성과 관련하여 설명하고, 상단 곡선은 조성과 관련된 증기의 온도를 나타냅니다. 확장에 의해, 상단 곡선은 증류액의 구성을 설명합니다.
문헌에서 발표된 증기-액체 평형 다이어그램을 사용하여 실험 중에 주어진 온도에서 액체와 증기의 구성을 식별할 수 있습니다. 이는 두 성분을 분리하기 위해 증류를 종료할 시기를 결정하는 데 도움이 될 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: 맥그로 힐.</li>
	<li style="font-size:17px">Felder, R.M., Rousseau, R.W. (2000). 화학 공정의 기본 원리. 뉴욕, NY : Wiley and Sons, Inc.</li>
</ol>

혼합성 혼합물의 증류
일부 액체는 실온의 열린 용기에 그대로 두면 시간이 지남에 따라 완전히 증발합니다. 그러나, 이것은 ...

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화학

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

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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

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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

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Separating Liquids by Boiling Point

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