Name: buffer ph and the common ion effect
Uploaded: 2020-03-26T07:22:25.000Z
Duration: 4 min 35 s
Channel: JoVE

완충액은 강산 또는 염기의 첨가에 관계없이 시스템에서 일정한 pH를 유지하기 위해 작동하는 용액입니다. 완충액이 없는 경우 용액에 강산 또는 염기를 추가하면 pH가 크게 변합니다. 완충 장치는 일상 생활에서 매우 중요합니다. 예를 들어, pH가 7.8 이상 또는 6.8 미만이면 사망에 이를 수 있으므로 혈액은 완충제 역할을 하며 pH를 7.35에서 7.45 사이로 유지할 수 있습니다.
그렇다면 버퍼는 어떻게 작동할까요? 완충액은 본질적으로 약산 또는 염기이며 서로 평형을 이루는 공액 염기 또는 산입니다. 예를 들어, 아세트산과 아세트산나트륨으로 만들어진 완충액을 생각해 보십시오. 완충 용액에는 약산과 그 공액 염이 포함되어 있으며, 이는 해리되어 공액 염기 아세테이트를 형성합니다. 용액은 아세트산의 Ka가 공액 염기의 Kb보다 높기 때문에 산성입니다.
해리 상수 Ka 또는 Kb는 물에서 화합물의 해리에 대한 평형 상수이기 때문에 각각 산 또는 염기의 강도를 정의한다는 것을 기억하십시오. 해리 상수는 pKa 또는 Ka의 음의 로그로 나타낼 수도 있으며, 여기서 pKa가 작을수록 산이 더 강합니다. pKb의 경우에도 마찬가지이며, pKb가 작을수록 밑이 강합니다.
아세테이트 완충액으로 돌아가서 수산화나트륨과 같은 강염기를 첨가하면 수산화물 이온이 용액에 존재하는 히드로늄 이온과 반응합니다. 이것은 평형 상태로 돌아가기 위해 더 많은 아세트산이 물과 반응하게 하여 더 많은 히드로늄 이온을 형성합니다. 염산과 같은 강산을 첨가하면 용액에 더 많은 히드로늄 이온이 형성됩니다. 이러한 이온은 아세테이트 이온과 반응하여 더 많은 아세트산을 형성합니다. 두 경우 모두 용액 pH의 변화는 거의 없습니다.
각 버퍼에는 용액을 버퍼링할 수 있는 특정 pH 범위가 있다는 점을 명심하십시오. 여기에서는 아세트산 완충액에 대한 적정 곡선을 보여줍니다. 버퍼링 범위가 강조 표시됩니다. 이 영역은 Henderson-Hasselbalch 방정식에 의해 결정되며, 이는 완충액의 pH가 약산의 Ka와 약산에 대한 공액 염기의 비율에 의해 결정된다는 것을 알려줍니다.
이 pH에서 멀리 떨어져 있으면 완충액의 약산 또는 염기가 고갈되어 pH를 완충할 수 없습니다. 따라서 응용 분야에 대한 버퍼를 선택할 때 pKa가 원하는 pH에 가까운 버퍼를 선택하십시오.
마지막으로, 모든 완충액은 완충 용량에 제한이 있으며, 이는 pH가 크게 변하기 전에 완충 용액에 추가할 수 있는 산 또는 염기의 양을 의미합니다. 예를 들어, 아세트산과 아세트산나트륨 완충 용액에 산을 너무 많이 첨가하면 모든 아세테이트 이온을 양성자화하고 많은 히드로늄 이온을 축적하여 pH를 낮춥니다.
마찬가지로, 염기를 너무 많이 추가하면 모든 아세트산을 탈양성자화하고 많은 수산화물 이온을 축적하여 pH를 증가시킵니다. 따라서, 완충 능력은 약산 및 공액 염의 농도에 의해 영향을받습니다. 따라서 1몰 아세테이트 완충액은 0.1몰 아세테이트 완충액보다 완충 용량이 더 높습니다.
이 실험실에서는 다양한 pH 범위의 완충액을 준비하고 검사합니다. 그런 다음 완충액을 사용하여 중성 적색이라고 하는 pH 지시약의 pKa를 측정하고 리보플라빈 결합 단백질이 도입될 때 중성 적색의 pKa의 변화를 탐색합니다.

버퍼

<h4>버퍼</h4>
Arrhenius acid(HA)를 물에 첨가하면 공액 염기(A-)와 수소 양이온(H+)으로 해리됩니다.
HA + H2O → H+(aq) + A-(aq)
용액에 존재하는 수소 이온의 양은 용액의 산도를 결정하며, 여기서 수소 이온이 많을수록 pH가 낮거나 산성이 더 높다는 것을 나타냅니다. 마찬가지로, 강한 Arrhenius 염기(BOH)가 물에 첨가되면 공액산(B+)과 수산화물 이온(OH-)으로 해리됩니다.
BOH + H2O → B+(aq) + OH-(aq)
일반적으로 용액에 강산 또는 염기를 첨가하면 산 또는 염기가 용액의 물 분자와 반응하여 수소 이온 또는 수산화물 이온의 농도가 증가하기 때문에 pH가 극적으로 변합니다. 그러나 이러한 pH 변화는 완충액을 사용하여 완화할 수 있습니다. 완충액은 강산 또는 염기의 첨가에 관계없이 시스템에서 일정한 pH를 유지하기 위해 작동하는 용액입니다.
대부분의 경우, 완충액의 구성 요소는 약산 또는 약염기의 공액 산-염기 쌍입니다. 이러한 이유로 물에서 완전히 해리되는 강산 또는 염기는 매우 불량한 완충액을 만들고 부분적으로 해리되는 약산 또는 염기는 더 나은 완충액을 만듭니다. 완충액이 존재할 때, 강산 또는 염기는 용액에 존재하는 물 분자와 반응하지 않고 대신 약산/공액 염기와 반응합니다. 그 결과 용액의 pH가 거의 또는 전혀 변하지 않습니다.
<h4>일반적인 이온 효과(Common Ion Effect)</h4>
버퍼는 공통 이온 효과(common ion effect)라고 하는 현상을 통해 작동합니다. 일반적인 이온 효과는 주어진 이온이 이미 주어진 이온을 포함하는 평형 상태의 혼합물에 추가될 때 발생합니다. 이런 일이 발생하면 평형은 더 많은 이온을 형성하는 것에서 멀어집니다.
예를 들어, 아세트산(CH3COOH)은 물에서 약간 해리되어 아세테이트 이온(CH3COO-)과 수소 이온을 형성합니다.
CH 3COOH(aq) H2O ⇔ H+(aq) + CH3COO-(aq)
용해성 아세트산나트륨에서 더 많은 아세테이트 이온이 첨가되면 평형 위치가 왼쪽으로 이동하여 더 많은 비해리 아세트산을 형성하고 수소 이온의 농도가 감소합니다. 여기서 일반적인 이온인 아세테이트는 아세트산의 해리를 억제합니다.
완충액은 용액을 완충하기 위해 산성(HA) 및 염기성(A-) 성분을 모두 고농도로 포함해야 합니다. 완충액에 첨가되는 수소 또는 수산화물 이온의 양이 적으면 소량의 한 완충액 성분이 다른 완충액으로 전환됩니다. 첨가된 이온의 농도가 완충액에 이미 존재하는 HA 및 A-의 농도보다 훨씬 작은 한, 첨가된 이온은 완충액 성분 중 하나에 의해 소비되기 때문에 pH에 거의 영향을 미치지 않습니다. 수소 또는 수산화물의 농도가 산 및 그 접합체 염기의 농도를 초과하면 완충 효과가 손실되고 pH가 변합니다.
<h4>Henderson-Hasselbalch 방정식</h4>
약산의 해리 상수 Ka는 비해리산 HA의 농도와 수소 이온 및 공액 염기의 농도 A-를 사용하여 계산됩니다.
<img src="/CDNSource/lm/labs/45/45_Concepts_4.jpg" alt="산 해리 상수 방정식 Ka=[H+][A-]/[HA], 화학식." data-altupdatedat="1754907201000">
Ka 값이 높을수록 더 강한 산을 나타내고 Ka 값이 작을수록 더 약한 산을 나타냅니다. 수소 이온의 농도를 결정하기 위해 방정식이 재배열됩니다. 이 형태에서는 염기종에 대한 산종의 비율이 수소 이온의 농도를 결정하고 더 나아가 pH를 결정하는 데 중요하다는 것이 분명합니다.
<img src="/CDNSource/lm/labs/45/45_Concepts_5.jpg" alt="산 해리 방정식, [H+] = Ka × [HA]/[A-], 화학 평형 개념." data-altupdatedat="1754907201000">
양쪽의 음의 공통 로그를 취하면 Henderson-Hasselbalch 방정식이 생성됩니다.
<img src="/CDNSource/lm/labs/45/45_Concepts_6.jpg" alt="Henderson-Hasselbalch 방정식; pH, pKa, 완충액, 산-염기 평형, 화학식." data-altupdatedat="1754907201000">
Henderson-Hasselbalch 방정식을 사용하면 수소 이온의 농도를 먼저 계산할 필요 없이 완충액 pH를 직접 계산할 수 있습니다.
예를 들어, 0.02 몰의 강염기를 첨가 한 후 1L 버퍼의 pH를 측정하는 데 사용할 수 있습니다. 강한 염기는 완전히 해리되므로 첨가된 수산기 이온의 농도는 0.02M입니다. 이것은 산의 농도를 0.02 감소시킵니다. 산(HA) 및 염기(A-) 성분의 원래 농도가 각각 0.5M라고 가정하면 염기의 새로운 농도는 0.02M에서 0.52M로 증가하는 반면 산의 농도는 0.02M에서 0.48M로 감소합니다. 완충액의 산 성분의 pKa를 알면 이러한 새로운 성분 농도를 Henderson-Hasselbalch 방정식으로 대체하여 pH를 결정할 수 있습니다.
이는 완충액 용량 또는 pH에 큰 영향을 주지 않고 완충액에 얼마나 많은 강산 또는 강염기를 추가할 수 있는지 결정하는 데 유용합니다.
<h4>버퍼 용량</h4>
완충 용량은 pH 변화에 저항하는 완충액의 능력을 측정한 것입니다. 이 능력은 완충액 성분의 농도, 즉 산과 그 공액 염기에 따라 달라집니다. 완충액 농도가 높을수록 완충액 용량이 더 큽니다. 이는 평형을 방해하고 완충액의 pH를 변경하기 위해 더 많은 양의 수소 이온 또는 더 강한 산을 첨가해야 함을 의미합니다.
완충 용량은 또한 완충 성분의 상대적 농도에 의해 영향을 받습니다. 완충액은 성분의 농도가 비슷할 때 더 효과적입니다. 완충액 성분 비율이 비슷하면 산 또는 염기가 첨가될 때 성분 농도 비율이 크게 변하지 않습니다. 비율을 상쇄하고 pH를 변경하기 위해 많은 양의 산 또는 염기를 첨가해야 합니다.
버퍼의 pH는 버퍼 용량과 다릅니다. pH 범위는 버퍼가 효과적인 범위입니다. 일반적으로 완충액은 완충액의 산 성분의 pKa의 1 pH 단위 내에서 사용 가능한 범위를 갖습니다.
<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">Silberberg, M.S. (2009). 화학: 물질과 변화의 분자적 성질. 매사추세츠주 보스턴: 맥그로 힐.</li>
</ol>

버퍼
Arrhenius acid(HA)를 물에 첨가하면 공액 염기(A-)와 수소 양이온(H+)으로 해리됩니다.
HA + H2O → H+(aq) + ...

Education

교육

JoVE Lab Manual

Chemistry

화학

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 contains a weak acid and its conjugate base, or a weak base and its conjugate acid. Weak acids and weak bases are better buffers because they dissociate only partially in water. When a buffer is present, added strong acid or base reacts with the buffer components instead of causing a large shift in pH.

The way buffers work is called the common ion effect. A common ion is an ion already present in an equilibrium mixture. When more of that ion is added, the equilibrium shifts away from making more of it. A good example is acetic acid, CH3COOH, which dissociates slightly in water to form H+ and acetate, CH3COO-. If sodium acetate adds more acetate ion, the equilibrium shifts left and less hydrogen ion remains in solution.

A buffer needs high amounts of both the acidic form, HA, and the basic form, A-. Small amounts of added H+ or OH- are used up by one buffer component and converted into the other. If the added acid or base is much smaller than the amounts already in the buffer, the pH changes very little. Once the concentration of added H+ or OH- becomes larger than the buffer components, the buffer effect is lost and the pH shifts.

The Henderson-Hasselbalch equation helps calculate buffer pH. It comes from the acid dissociation constant, Ka, which uses the concentrations of HA, H+, and A-. A larger Ka means a stronger acid, while a smaller Ka means a weaker acid. After rearranging and taking the negative log, the equation shows that the ratio of acid to base controls pH, so buffer pH can be found without first calculating hydrogen ion concentration.

For example, a 1 L buffer with 0.5 M HA and 0.5 M A- can change after 0.02 moles of strong base are added. The strong base dissociates completely, so 0.02 M OH- is present. That amount lowers the acid concentration to 0.48 M and raises the base concentration to 0.52 M. The new values can be placed into the Henderson-Hasselbalch equation with the acid pKa to find the pH. This also helps estimate buffer capacity, or how much strong acid or strong base a buffer can absorb without a large pH change.

Buffer capacity depends on concentration. A more concentrated buffer has a greater ability to resist pH change. It also depends on how similar the acid and base concentrations are. Buffers work best when those concentrations are close, because the ratio changes only a little when acid or base is added. Buffer pH is not the same as buffer capacity. The effective pH range is usually within 1 pH unit of the acid component's pKa.

Buffer pH and the Common Ion Effect

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 solutions help keep pH steady when acids or bases are added. In water, an Arrhenius acid (HA) dissociates into hydrogen ions, H+, and a conjugate base, A-. More hydrogen ions make a solution more acidic and lower its pH. An Arrhenius base (BOH) dissociates into a conjugate acid, B+, and hydroxide ions, OH-. Strong acids and strong bases usually change pH a lot because they react completely in water and raise the amount of H+ or OH-. Buffers reduce those pH changes. A buffer usually...

enthalpy of reaction

Reaction Heat, Hess’s Law, and Calorimetry

Reaction heat is explained through enthalpy, Hess’s law, and calorimetry. These ideas show how heat moves during chemical reactions and how scientists measure it. Thermodynamics is the study of heat energy and other forms of energy, such as work. Its laws are used across science, from biology to physics. The first law says energy is conserved in an isolated system. Energy can change form, such as thermal energy becoming work, but it cannot be created or destroyed. The second law of...

solubility

Solubility in Water and Other Solvents

Solubility describes how much of a solute can dissolve in a specific solvent. It is usually reported as solute mass per solvent volume or as solute mass per solvent mass. For example, sodium chloride has a solubility of 36 g per 100 mL of water at room temperature. If solubility is given by solvent mass, that mass must be converted to volume for later calculations. Temperature changes solubility. Sodium carbonate dissolves at about 7 g per 100 mL of water at 0 °C, 22 g per 100 mL at room...

metal flame emission

Flame Test Metal Color Clues

Flame testing uses a metal sample and a flame to identify a substance by its color. Each element gives off a characteristic light emission in the flame, so the color can help distinguish one element from another. This same idea appears in fireworks, where different metal components create different colors. The color comes from energy absorbed by the metallic component. When a species absorbs energy, that energy can go into translation, vibration, rotation, or electron excitement. Electron...

balmer series

Hydrogen Emission Lines

Hydrogen emission lines show how electrons move between fixed energy levels in the Bohr model. Niels Bohr proposed this model for the hydrogen atom in 1913. In this model, an electron can only occupy certain orbits, and it cannot exist between them. These energy states are labeled with the quantum number n. The ground state is n = 1. Higher values, such as n = 2, 3, 4, and so on, are excited states. An electron changes state only by absorbing or emitting energy equal to the difference between...

beer's law

Absorbance Spectra and Beer-Lambert Analysis

Absorbance spectra and the Beer-Lambert Law show how light can be used to study molecules in solution. When light hits a substance, it may be absorbed, transmitted, or reflected. A substance often interacts with a range of wavelengths, and each wavelength can affect the molecules or atoms in a different way. When a molecule absorbs light, that energy can be used for translation, vibration, rotation, or electron excitement. Electron excitement is especially important in spectroscopy because it...

concentration dependence

Reaction Order and Rate Constants

Chemical kinetics describes the speed of a chemical reaction. The rate depends on the reaction mechanism, the complexity of the reaction, and the number of reactants involved. Reactant concentration also affects how fast a reaction happens. The rate law is the experimental relationship that connects these factors to reaction rate. In the rate law, each reactant contributes through a reaction order. The general form is r = k[A]^m[B]^n for aA + bB + ... → cC. Here, r is the reaction rate, k is...

temperature dependence

Reaction Rate, Arrhenius, and Catalysts

Chemical kinetics explains how fast a reaction happens and why that speed changes. The reaction rate is the speed of a chemical reaction. It is defined as the change in concentration of a reactant or product over time. Reaction speed depends on several factors, including the concentration of the reactants and the temperature of the reaction. Each reactant affects the rate in a specific way. That relationship is described by the rate law. The rate law is an equation that connects the...

galvanic cells

Battery Power from Redox Reactions

Electrochemistry studies how chemical change and electrical energy are linked. In this branch of chemistry, electrons move from one species to another. That movement can either produce current or be driven by an applied current. The main reaction in electrochemistry is the oxidation-reduction, or redox, reaction. A redox reaction has two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. These changes also shift the oxidation state of each substance. The...

electrolytic cells

Electroplating with Electrolytic Cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the...

proper lab notebook keeping

Recording a Reproducible Lab Experiment

Accurate lab notebook records are essential in science and organic chemistry labs. Without clear notes, descriptions, quantities, and observations, an experiment cannot be repeated or checked. Good record keeping supports reproducibility, which means other people can follow the same work and get similar results. A laboratory notebook is useful in school labs, research settings, and industry. It can also become a legal record when an idea, process, substance, or technique is patented and...

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

Organic chemistry labs use specific glassware, careful weighing steps, and controlled heating to keep reactions safe and accurate. Beakers and Erlenmeyer flasks are often used for mixing or holding solvents, but they are not meant for measuring volume unless only an approximate amount is needed. Volumetric glassware is used when a precise volume matters. This group includes graduated cylinders, volumetric pipettes, and volumetric flasks. A graduated cylinder is commonly used in the organic lab...

melting points

How Impurities Change Melting Points

Melting point helps identify an organic compound by showing the temperature where a solid turns into a liquid at 1 atmosphere of pressure. It is a physical property, like solubility, density, color, and electronegativity. Because the exact start of melting is hard to measure, the result is reported as a range. The lower end is when the first drops of liquid appear. The upper end is when the last solid has melted. Scientists compare this range with literature values to help identify a compound. <br...

boiling points

Boiling Point and Vapor Pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

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

화학 실험실에서 꼭 필요한 기본 커리큘럼 중심 비디오입니다.

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

Learn how buffers resist pH change through the common ion effect, the Henderson-Hasselbalch equation, and buffer capacity in high school chemistry.

Buffer pH and the Common Ion Effect | JoVE K12

8분 길이의 강사용 가이드를 통해 버퍼 수업을 준비하세요. JoVE Lab Manual의 Chemistry 실험을 위한 핵심 준비 단계를 다룹니다.

Chemistry의 버퍼 강사용 준비 - 8.0K+ 조회수 | JoVE Lab Manual

15분 길이의 학생 프로토콜 영상을 통해 버퍼 절차를 단계별로 따라 해보세요. JoVE Lab Manual의 Chemistry 컬렉션의 일부입니다.

Chemistry의 버퍼 학생 프로토콜 - 25K+ 조회수 | JoVE Lab Manual

Buffer pH and the Common Ion Effect

Description

Transcript

Tags