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

Los tampones son soluciones que trabajan para mantener un pH constante en un sistema, independientemente de la adición de ácidos o bases fuertes. En ausencia de tampones, la adición de un ácido fuerte o una base a una solución cambia significativamente el pH. Los amortiguadores son cruciales en la vida cotidiana. Por ejemplo, la sangre actúa como un amortiguador y es capaz de mantener un pH entre 7,35 y 7,45, ya que un pH superior a 7,8 o inferior a 6,8 puede causar la muerte.
Entonces, ¿cómo funciona un búfer? Un tampón es esencialmente un ácido o base débil y su base conjugada o ácido en equilibrio entre sí. Tomemos, por ejemplo, un tampón hecho de ácido acético y acetato de sodio. La solución tampón contiene un ácido débil y su sal conjugada, que se disocia para formar el acetato base conjugado. La solución es ácida porque el Ka del ácido acético es mayor que el Kb de la base conjugada.
Recordemos que la constante de disociación, Ka o Kb, define la fuerza del ácido o de la base, respectivamente, ya que es la constante de equilibrio para la disociación del compuesto en agua. La constante de disociación también se puede representar como pKa, o el logaritmo negativo de Ka, donde cuanto menor es el pKa, más fuerte es el ácido. Lo mismo ocurre con el pKb, donde cuanto más pequeño es el pKb, más fuerte es la base.
Volviendo al tampón de acetato, si añadimos una base fuerte, como el hidróxido de sodio, los iones hidróxido reaccionan con los iones hidronio presentes en la solución. Esto hace que más ácido acético reaccione con el agua para volver al equilibrio, formando así más iones de hidronio. Si añadimos un ácido fuerte, como el ácido clorhídrico, se forman más iones de hidronio en solución. Esos iones reaccionan con los iones de acetato para formar más ácido acético. En ambos casos, hay muy poco cambio en el pH de la solución.
Tenga en cuenta que cada tampón tiene un rango de pH específico en el que puede amortiguar una solución. Aquí mostramos una curva de valoración para nuestro tampón de ácido acético. Se resalta el rango de almacenamiento en búfer. Esta región está determinada por la ecuación de Henderson-Hasselbalch, que nos dice que el pH del tampón está determinado por el Ka del ácido débil y la relación entre la base conjugada y el ácido débil.
Lejos de este pH, el ácido débil o la base del tampón se agota y no puede amortiguar el pH. Por lo tanto, al seleccionar un tampón para su aplicación, elija uno cuyo pKa esté cerca del pH deseado.
Finalmente, todos los tampones tienen un límite en su capacidad de tampón, es decir, la cantidad de ácido o una base que se puede agregar a la solución tampón antes de que el pH cambie significativamente. Por ejemplo, si añadimos demasiado ácido a nuestra solución tampón de ácido acético y acetato de sodio, protonaremos todos los iones de acetato y acumularemos una gran cantidad de iones hidronio, disminuyendo así el pH.
Del mismo modo, si añadimos demasiada base, desprotonaremos todo el ácido acético y acumularemos una gran cantidad de iones de hidróxido, aumentando así el pH. Por lo tanto, la capacidad amortiguadora está influenciada por la concentración del ácido débil y la sal conjugada. Por lo tanto, un tampón de acetato de 1 molar tiene una mayor capacidad de amortiguación que un tampón de acetato de 0,1 molar.
En este laboratorio, preparará y examinará tampones con una amplia variedad de rangos de pH. A continuación, utilizará sus tampones para determinar el pKa de un indicador de pH, llamado rojo neutro, y explorará el cambio en el pKa del rojo neutro cuando se introduce la proteína de unión a la riboflavina.

búferes

<h4>Búferes</h4>
Cuando se agrega un ácido Arrhenius (HA) al agua, se disocia en su base conjugada (A-) y un catión de hidrógeno (H+).
HA + H2 O →H+(aq) + A-(aq)
La cantidad de iones de hidrógeno presentes en la solución determina la acidez de la solución, donde más iones de hidrógeno indican un pH más bajo o más ácido. De manera similar, cuando se agrega una base fuerte de Arrhenius (BOH) al agua, se disocia en su ácido conjugado (B+) y un ion hidróxido (OH-).
BOH + H2O → B+(aq) + OH-(aq)
Generalmente, la adición de ácidos o bases fuertes a una solución cambia drásticamente el pH porque el ácido o la base reacciona con las moléculas de agua en la solución, aumentando la concentración de iones de hidrógeno o iones de hidróxido. Sin embargo, este cambio en el pH se puede mitigar utilizando un tampón. Los tampones son soluciones que trabajan para mantener un pH constante en un sistema, independientemente de la adición de ácidos o bases fuertes.
La mayoría de las veces, los componentes de un tampón son el par ácido-base conjugado de un ácido débil o una base débil. Por esta razón, los ácidos o bases fuertes que se disocian completamente en el agua hacen tampones muy pobres y los ácidos o bases débiles que se disocian parcialmente hacen mejores tampones. Cuando el tampón está presente, el ácido fuerte o la base no reacciona con las moléculas de agua presentes en la solución y, en cambio, reacciona con el ácido débil / base conjugada. Esto da como resultado poco o ningún cambio en el pH de la solución.
<h4>El efecto común de los iones</h4>
Un tampón funciona a través de un fenómeno llamado efecto iónico común. El efecto de iones comunes ocurre cuando un ion dado se agrega a una mezcla en equilibrio que ya contiene el ion dado. Cuando esto sucede, el equilibrio se aleja de la formación de más de ese ion.
Por ejemplo, el ácido acético (CH3COOH) se disocia ligeramente en el agua, formando el ion acetato (CH3COO-) y el ion hidrógeno.
CH3COOH(aq) H2O ⇔ H+(aq) + CH3COO-(aq)
Si se agrega más ion acetato del acetato de sodio soluble, la posición de equilibrio se desplaza hacia la izquierda para formar más ácido acético no disociado y la concentración de iones de hidrógeno disminuye. Aquí, el ion común, el acetato, suprime la disociación del ácido acético.
Un tampón debe contener altas concentraciones de los componentes ácidos (HA) y básicos (A-) para tampón una solución. Si la cantidad de iones de hidrógeno o hidróxido añadidos al tampón es pequeña, hacen que una pequeña cantidad de un componente del tampón se convierta en el otro. Siempre que la concentración de iones añadidos sea mucho menor que las concentraciones de HA y A- ya presentes en el tampón, los iones añadidos tendrán poco efecto sobre el pH, ya que son consumidos por uno de los componentes del tampón. Cuando la concentración de hidrógeno o hidróxido excede las concentraciones del ácido y su base conjugada, se pierde el efecto amortiguador y el pH cambiará.
<h4>Ecuación de Henderson-Hasselbalch</h4>
La constante de disociación, Ka, de un ácido débil se calcula utilizando las concentraciones del ácido no disociado HA y las concentraciones de los iones de hidrógeno y la base conjugada, A-.
<img src="/CDNSource/lm/labs/45/45_Concepts_4.jpg" alt="Ecuación constante de disociación ácida Ka = [H +] [A-] / [HA], fórmula química." data-altupdatedat="1754907201000">
Los valores más altos de Ka representan ácidos más fuertes, mientras que los valores más bajos de Ka representan ácidos más débiles. Para determinar la concentración de iones de hidrógeno, se reorganiza la ecuación. De esta forma, está claro que la proporción de especies ácidas con respecto a las especies básicas es importante para determinar la concentración de iones de hidrógeno y, por extensión, el pH.
<img src="/CDNSource/lm/labs/45/45_Concepts_5.jpg" alt="Ecuación de disociación ácida, [H+] = Ka × [HA]/[A-], concepto de equilibrio químico." data-altupdatedat="1754907201000">
Tomando el logaritmo común negativo de ambos lados se obtiene la ecuación de Henderson-Hasselbalch.
<img src="/CDNSource/lm/labs/45/45_Concepts_6.jpg" alt="ecuación de Henderson-Hasselbalch; pH, pKa, solución tampón, equilibrio ácido-base, fórmula química." data-altupdatedat="1754907201000">
La ecuación de Henderson-Hasselbalch permite calcular el pH del tampón directamente, sin tener que calcular primero la concentración de iones de hidrógeno.
Por ejemplo, se puede utilizar para determinar el pH de un tampón de 1 L después de añadir 0,02 moles de una base fuerte. La base fuerte se disocia completamente, por lo que la concentración de iones hidroxilo agregados es de 0,02 M. Esto disminuirá la concentración del ácido en 0,02. Suponiendo que la concentración original de los componentes ácido (HA) y base (A-) es cada uno de 0,5 M, la nueva concentración de base aumenta en 0,02 M a 0,52 M, mientras que la concentración de ácido disminuye en 0,02 M a 0,48 M. Conociendo el pKa del componente ácido del tampón, podemos sustituir estas nuevas concentraciones de componentes en la ecuación de Henderson-Hasselbalch para determinar el pH.
Esto es útil para determinar la capacidad del tampón, o la cantidad de ácido fuerte o base fuerte que se puede agregar a un tampón sin afectar significativamente el pH.
<h4>Capacidad del búfer</h4>
La capacidad del tampón es la medida de la capacidad de un tampón para resistir el cambio de pH. Esta capacidad depende de la concentración de los componentes tampón, es decir, el ácido y su base conjugada. Una mayor concentración de tampón tiene una mayor capacidad tampón. Esto significa que habría que añadir una mayor cantidad de iones de hidrógeno, o un ácido más fuerte, para alterar el equilibrio y cambiar el pH del tampón.
La capacidad del tampón también se ve afectada por las concentraciones relativas de los componentes del tampón. El tampón es más eficaz cuando las concentraciones de los componentes son similares. Si la proporción de componentes tampón es similar, entonces la relación de concentración de componentes no cambia significativamente cuando se agrega ácido o base; Se deben agregar grandes cantidades de ácido o base para compensar la proporción y cambiar el pH.
El pH del tampón difiere de su capacidad tampón. El rango de pH es el rango en el que el tampón es efectivo. Por lo general, los tampones tienen un rango utilizable dentro de 1 unidad de pH del pKa del componente ácido del tampón.
<h4>Referencias</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Química y reactividad química. Belmont, CA: Brooks/Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silberberg, M.S. (2009). Química: La naturaleza molecular de la materia y el cambio. Boston, MA: McGraw Hill.</li>
</ol>

Búferes

Búferes
Cuando se agrega un ácido Arrhenius (HA) al agua, se disocia en su base conjugada (A-) y un catión de hidrógeno (H+).
HA + H2O → H+(aq) + ...

Education

Educación

JoVE Lab Manual

Chemistry

Química

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

Videos completos y enfocados en el plan de estudios, tanto para los instructores como para los estudiantes de los cursos de laboratorio de introducción a la química.

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

Prepárese para enseñar Búferes con esta guía para instructores de 8 minutos. Cubre los pasos clave de preparación para el laboratorio Chemistry en JoVE Lab Manual.

Preparación del instructor para Búferes en Chemistry - Más de 8.0K visualizaciones | JoVE Lab Manual

Siga los procedimientos paso a paso de Búferes en este video de protocolo estudiantil de 15 minutos. Parte de la colección Chemistry en JoVE Lab Manual.

Protocolo estudiantil de Búferes en Chemistry - Más de 25K visualizaciones | JoVE Lab Manual

Buffer pH and the Common Ion Effect

Description

Transcript

Tags