Name: separating mixtures by polarity
Uploaded: 2020-03-26T07:22:28.000Z
Duration: 3 min 7 s
Channel: JoVE

كروماتوغرافيا العمود هي تقنية تستخدم عمودا معبأا لفصل المركبات بناء على تفاعلاتها مع الطور الثابت ، والتي عادة ما تكون على شكل حبات مجهرية. تمتلئ الفراغات بين الخرزات بالمذيبات. يسمح فتح العمود للمذيب بالتدفق عبر المرحلة الثابتة. عندما يتم تطبيق خليط على الجزء العلوي من العمود المعبأ متبوعا بمزيد من المذيب ، ينتقل الخليط إلى المرحلة المتحركة ويتدفق عبر المرحلة الثابتة. 
يتفاعل كل مكون من مكونات الخليط مع المرحلة الثابتة بطريقة مختلفة. بعض المكونات لها تفاعلات ضعيفة مع المرحلة الثابتة وبالتالي تتحرك بسرعة عبر العمود ، بينما يكون للآخرين تفاعلات قوية مع المرحلة الثابتة وبالتالي تتحرك بشكل أبطأ. هذا يفصل المركبات المختلفة إلى نطاقات يتم جمعها في أجزاء صغيرة. هذا يتيح تنقية كل مركب. 
إذن ، ما نوع الخصائص التي يمكن استخدامها لفصل الخلائط؟ واحدة من أكثر الخصائص استخداما هي القطبية. لهذا الغرض ، غالبا ما يستخدم هلام السيليكا ، وهو شكل من أشكال ثاني أكسيد السيليكون ، كمرحلة ثابتة. يتفاعل هلام السيليكا مع المركبات عن طريق تفاعلات ثنائي القطب ثنائي القطب والترابط الهيدروجيني من خلال مجموعات -OH التي تتشكل على سطحه. وبالتالي ، ستتفاعل المركبات القطبية بقوة مع المرحلة الثابتة ، بينما تتفاعل المركبات غير القطبية بشكل ضعيف. 
تشمل الخصائص الأخرى التي يمكن استغلالها للفصل الحجم والشحنة وكراهية الماء. الطريقة الشائعة لتحميل المرحلة الثابتة في العمود هي ملاط الطور الثابت والمذيب. بعد ذلك ، يتم تعبئة المرحلة الثابتة عن طريق تدفق المزيد من المذيبات عبر العمود لضغط الملاط. من الضروري أن تكون المرحلة الثابتة معبأة بشكل موحد بدون فقاعات هواء أو قنوات فارغة أو بقع جافة. يمكن أن تعطل هذه التدفق وتسبب اختلاط العصابات. 
عند اختيار عمود ، يعتمد القطر على حجم العينة المراد فصلها. يجب أن تغطي العينة الجزء العلوي من العمود بطبقة رقيقة ومتساوية. تؤدي طبقة العينة السميكة إلى نطاقات أوسع. يعتمد طول العمود على مدى جودة انفصال المركبات في المرحلة الثابتة. تتطلب المركبات ذات الصلات المتشابهة للمرحلة الثابتة عمودا طويلا للفصل المناسب. ومع ذلك ، يمكن فصل مزيج من المركبات ذات الصلات المختلفة جدا للمرحلة الثابتة على عمود أقصر. 
في هذا المختبر ، سوف تستكشف كروماتوغرافيا العمود عن طريق تعبئة عمود هلام السيليكا وإعداده أولا. بعد ذلك ، ستستخدم العمود الخاص بك لفصل المكونات الملونة في صبغة الطعام الخضراء.

كروماتوغرافيا العمود

كروماتوغرافيا العمود
توجد تقنيات متعددة لتنقية وفصل المركبات في مختبر الكيمياء العضوية. واحدة من أكثر تقنيات الفصل موثوقية للفصل المجهري ، حيث يتوفر أقل من 10 جرامات من المركب للتحليل ، هي كروماتوغرافيا العمود. تفصل هذه التقنية المركبات في خليط بناء على خصائصها الفيزيائية ، مثل قابليتها للذوبان والقطبية والكراهية للماء وحجمها وشحنتها. 
<h4>أساسيات الكروماتوغرافيا</h4>
المكونات الرئيسية لأي نظام كروماتوغرافيا هي المرحلة الثابتة والمرحلة المتحركة وخليط العينة المراد تحليله. في كروماتوغرافيا العمود ، عادة ما تكون المرحلة الثابتة عبارة عن خرز دقيق ، يتم تعبئتها بشكل موحد في عمود عمودي. يضاف تدفق مستمر للطور المتحرك ، المعروف أيضا باسم المذيب ، إلى الجزء العلوي من العمود ، والذي يتدفق عبر المرحلة الثابتة عن طريق الجاذبية أو بمعدل تدفق متحكم فيه بواسطة مضخة. 
تذوب العينة بكمية صغيرة من المذيب ثم تضاف إلى أعلى العمود. يضاف المزيد من المذيبات لإجبار العينة على التدفق عبر المرحلة الثابتة. تنقسم المركبات الموجودة في الخليط بين المرحلة المتحركة والمرحلة الثابتة بناء على خصائصها المختلفة وتشكل نطاقات منفصلة. 
ستتحرك المركبات ذات التفاعلات القوية مع الطور الثابت بشكل أبطأ من المركبات ذات التفاعلات الضعيفة مع الطور الثابت. وبالتالي ، فإن المركبات ذات التفاعلات الضعيفة ستخرج من العمود ، أو العزف ، في وقت أبكر من تلك ذات التفاعلات القوية. يتم تحديد قوة تفاعل المركب مع الطور الثابت من خلال عامل التخلف (R f ) ، وهي نسبة المسافة التي يقطعها المكون إلى تلك التي تقطعها المرحلة المتنقلة. يتم تحديد عامل التخلف عن طريق إجراء كروماتوغرافيا الطبقة الرقيقة أولا. 
<img src="/CDNSource/lm/labs/63/63_Concepts_1.jpg">
تشير قيمة عامل التأخير العالية إلى أن العينة تتفاعل بقوة مع المرحلة الثابتة وتستغرق وقتا طويلا للعزف. تشير قيمة عامل التخلف المنخفضة إلى أن العينة لا تتفاعل مع المرحلة الثابتة بقوة شديدة وتمحله بسرعة أكبر. نظرا لأن المركبات تنقسم إلى نطاقات فردية وتتخلص من العمود في أوقات مختلفة بسبب قيم R f المختلفة ، فيمكن عزلها بشكل فردي عن طريق جمع المذيب من أسفل العمود في كسور. 
<h4>اعتبارات كروماتوغرافيا العمود</h4>
عمود الكروماتوغرافيا عبارة عن أنبوب زجاجي أو بلاستيكي موجه عموديا. يمكن أن يتراوح حجم العمود من بضعة سنتيمترات (مثل ماصة باستور) إلى أمتار (مثل الأعمدة الصناعية). يعتمد قطر العمود على كمية العينة المراد فصلها ، بينما يعتمد طول العمود على صعوبة الفصل. يتطلب التقسيم الأكثر كفاءة إلى نطاقات منفصلة طبقات عينة رقيقة ؛ لذلك ، يعد تحديد القطر المناسب خطوة حيوية. سيؤدي تحميل حجم عينة كبير جدا بالنسبة لقطر العمود إلى إنشاء نطاقات أوسع وأقل تحديدا من نفس حجم العينة في عمود بقطر أكبر. 
عند اختيار طول العمود، يجب مراعاة قيم Rf للمكونات. قد يكون من الصعب فصل المكونات ذات عوامل التخلف المتشابهة وتتطلب عمودا أطول لحل النطاقات الفردية. قد لا تحتاج المركبات ذات عوامل التخلف المختلفة جدا إلى عمود طويل ، حيث يجب أن تنقسم بسهولة. عند اختيار المرحلة الثابتة ، من المهم اختيار المرحلة التي تؤدي إلى عوامل تأخر مختلفة لكل مكون. 
يعد إعداد العمود هو الجزء الأكثر أهمية في تشغيل عمود كروماتوغرافيا. يجب أن تكون كتلة المرحلة الثابتة المعبأة في العمود 20 ضعفا على الأقل من كتلة العينة. إذا لم يكن العمود يحتوي على قرص مسامي في الأسفل ، فيجب أن يكون معبأا بالقطن وطبقة رقيقة من الرمل. هذا يمنع فقدان المرحلة الثابتة من خلال خروج العمود. 
هناك طريقتان لتعبئة العمود: طريقة التعبئة الجافة وطريقة الطين. في الطريقة الجافة ، يتم نقل المرحلة الثابتة إلى العمود في شكل مسحوق. ثم يتم غسل العمود عدة مرات باستخدام الطور / المذيب المتحرك للتأكد من أن المذيب يخترق كل جزء من عمود هلام السيليكا. هذه الطريقة ، إذا لم يتم إجراؤها بشكل صحيح ، يمكن أن تزيد من احتمالية تشكل البقع الجافة والقنوات وفقاعات الهواء في العمود. ستؤثر هذه العيوب على قدرة العمود على تقسيم مكونات الخليط. 
توفر طريقة الملاط عمودا معبأا أكثر اتساقا لا يحتوي على فقاعات هواء ومناطق جافة وقنوات. لهذه الطريقة ، يتم خلط المرحلة الثابتة مع مذيب لتشكيل ملاط متسق. ثم يتم نقل الملاط إلى العمود أثناء النقر على الجانبين للتخلص من أي فقاعات هواء متكونة. يجب أن يكون محبس العمود ، إذا كان هناك واحد ، مفتوحا خلال هذه الخطوة للسماح للمذيب بالتصريف. 
<h4>كروماتوغرافيا هلام السيليكا</h4>
يتم استغلال العديد من الخصائص المختلفة لفصل مزيج من المركبات ، مثل الحجم والشحنة والكراهية للماء. إحدى الخصائص المستخدمة لفصل المركبات في الكيمياء العضوية هي القطبية. لهذا الغرض ، يعد هلام السيليكا وهلام الألومينا أكثر المراحل الثابتة شيوعا. هلام السيليكا قطبي للغاية ويشكل تفاعلات ثنائية القطب قوية مع المركبات القطبية. بالإضافة إلى ذلك ، يمكن أن يشكل هلام السيليكا روابط هيدروجينية مع المادة التحليلية بسبب وجود مجموعات -OH على سطحه. 
ترتبط مكونات الخليط الأكثر قطبية بقوة بهلام السيليكا وتنتقل ببطء عبر العمود ، في حين أن المكونات غير القطبية تكون أكثر قابلية للذوبان في المرحلة المتحركة وتنتقل بسرعة عبر العمود. وبالتالي ، من الضروري أن يكون لمكونات الخليط أقطاب مختلفة. يتم التخلص من المكونات التي تتفاعل بقوة مع المرحلة الثابتة عن طريق تدفق طور قطبي متحرك عبر العمود. 
<h4>المراجع</h4>
<ol>
	<li style="font-size:17px">شولر ، إم إل ، كارجي ، ك. ، ديليزا ، م. (2017). هندسة العمليات الحيوية ، المفاهيم الأساسية. نهر السرج العلوي ، نيوجيرسي: قاعة برنتيس. </li>
	<li style="font-size:17px">هاريس ، العاصمة (2015). التحليل الكيميائي الكمي. نيويورك ، نيويورك: دبليو إتش فريمان وشركاه. </li>
</ol>

كروماتوغرافيا العمود
توجد تقنيات متعددة لتنقية وفصل المركبات في مختبر الكيمياء العضوية. واحدة من أكثر الفصل موثوقية ...

Education

JoVE Lab Manual

Chemistry

الكيمياء

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 made of microscale beads packed into a vertical column. The mobile phase is a solvent that flows through the column by gravity or at a controlled rate with a pump. The sample is first dissolved in a small amount of solvent, added to the top of the column, and then pushed through with more solvent.

As the mixture moves through the column, its compounds partition between the two phases. They form separate bands because each compound interacts differently with the stationary phase. Compounds that interact strongly move more slowly. Compounds with weaker interactions elute, or leave the column, earlier. The retardation factor, or Rf, describes this interaction by comparing how far a component travels with how far the mobile phase travels. A high Rf means strong interaction and slow elution. A low Rf means weaker interaction and faster elution. The Rf is determined first with thin layer chromatography, and the separated compounds are collected in fractions as they leave the column.

The size and shape of the column affect how well the separation works. A chromatography column is a vertical glass or plastic tube that can range from a few centimeters, such as a Pasteur pipette, to meters in industrial systems. The column diameter depends on the amount of sample, and the length depends on how difficult the separation is. Thin sample layers give the best band separation, so using the right diameter is important. If too much sample is loaded for the column diameter, the bands become broader and less defined. When components have similar Rf values, a longer column may be needed to separate them. If their Rf values are very different, a shorter column may still work well. The stationary phase should also be chosen so the components have different Rf values.

Packing the column correctly is one of the most important steps. The stationary phase should weigh at least 20 times more than the sample. If there is no porous disk at the bottom, cotton and a thin layer of sand are used to stop the stationary phase from leaving the column. The column can be packed by a dry method or by a slurry method. In the dry method, the powder is added directly and then washed with solvent so the mobile phase can move through the silica gel. If this step is not done well, dry patches, channels, and air bubbles can form. These defects reduce how well the mixture separates. The slurry method mixes the stationary phase with solvent first, then transfers it into the column while tapping the sides to remove bubbles. If the column has a stopcock, it should be open so the solvent can drain.

Silica gel chromatography is a common way to separate compounds by polarity. Silica gel and alumina gel are the most used stationary phases for this purpose. Silica gel is very polar and can form dipole-dipole interactions and hydrogen bonds because of its -OH groups. Polar components bind more strongly to silica gel and move slowly through the column. Non-polar components stay more soluble in the mobile phase and move faster. Because of this, the mixture must contain components with different polarities. More polar compounds are eluted by using a polar mobile phase through the column.

Separating Mixtures by Polarity

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

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

Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

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

Learn how column chromatography separates mixtures by polarity, Rf values, and band movement through a packed column using silica gel and solvents.

Separating Mixtures by Polarity | JoVE K12

استعد لتدريس كروماتوغرافيا العمود من خلال هذا الدليل الإرشادي للمدرسين لمدة 3 دقيقة. يغطي خطوات التحضير الأساسية لمختبر Chemistry على JoVE Lab Manual.

تحضير المدرّس لـ كروماتوغرافيا العمود في Chemistry - أكثر من 9.4K مشاهدة | JoVE Lab Manual

اتبع إجراءات كروماتوغرافيا العمود خطوة بخطوة في فيديو بروتوكول الطالب هذا لمدة 9 دقيقة. جزء من مجموعة Chemistry على JoVE Lab Manual.

بروتوكول الطالب لـ كروماتوغرافيا العمود في Chemistry - أكثر من 43K مشاهدة | JoVE Lab Manual

Separating Mixtures by Polarity

Description

Transcript