Name: acids, bases, and ph in titration
Uploaded: 2020-03-26T07:22:25.000Z
Duration: 6 min 35 s
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Chemistry

1.2.1 9L.4.2.2.1

Acid and Base Concentrations

阿伦尼乌斯酸是指在水中溶解时能产生氢离子的物质，而碱则产生氢氧根离子。氢离子会立即与水反应生成水合氢离子，但为了简化起见，我们仍将其视为氢离子。根据溶液中氢离子或氢氧根离子含量的多少，溶液被认定为酸性或碱性。
我们使用pH值来衡量酸碱度，pH值等于氢离子浓度的负对数。因此，pH值低于7为酸性，高于7为碱性，pH值等于7为中性。
酸和碱还可以根据其强度进行比较，这与它们的pH值不同。酸的强度与其氢离子从阴离子（称为共轭碱）上解离的难易程度有关。对于碱而言，同样可以根据氢氧根离子及其共轭酸的关系来理解这一概念。我们可以通过酸解离常数（即Ka）来量化这种强度。
Ka 通过未解离酸以及解离出的氢离子和共轭碱的浓度来定义。你经常会看到此关系表示为 pKa，它就是 Ka 的负对数。pKa 越小，酸性越强。
一些酸（如盐酸）是一元酸，意味着它们只能解离出一个氢离子。多元酸（如磷酸）则可以解离出多个氢离子。每一次解离都有其对应的pKa值。
那么，我们如何测定 pKa 呢？一种方法是进行酸碱滴定。滴定是通过将已知浓度的溶液缓慢加入到未知浓度的溶液中，同时观察两者之间的反应。在此过程中，酸与碱发生中和反应，生成盐和水。
因此，如果我们想要测定酸中氢离子的浓度，只需使用已知氢氧根离子浓度的强碱进行滴定，直至酸被完全中和。为了准确地进行滴定，需要对碱进行标定——即必须准确知道其氢氧根离子的精确浓度。这并不总是简单的。
例如，您在实验中将使用的 NaOH 具有很强的吸湿性，这意味着它会从空气中吸收水分。无论是固体还是溶液状态，NaOH 都会发生这种现象。因此，NaOH 溶液的实际浓度可能低于您的预期。
为了确定 NaOH 的准确浓度，我们必须首先进行酸碱滴定。为此，需使用该碱滴定一种已知浓度的酸。邻苯二甲酸氢钾（KHP）是一种非吸湿性酸，因此我们可以根据其质量准确计算出其浓度。
我们可以通过使用酚酞等 pH 指示剂来判断滴定是否完成——即酸已被中和。酚酞在 pH 约 0 至 pH 8 之间呈中性且无色。
随着pH升高，两个氢离子解离。这种阴离子形式呈粉红色。因此，当我们开始滴定时，KHP溶液呈酸性，酚酞为无色。随着我们加入NaOH，氢离子被中和，pH逐渐升高。
在此反应中，当酸和碱以等量混合时，溶液呈中性。此后，再加入少量 NaOH 会使 pH 值变为碱性，溶液变为粉红色。这被称为滴定终点。如果我们知道 KHP 的物质的量以及用于中和它的 NaOH 的体积，就可以计算出碱的准确浓度。
有了标准化的碱溶液后，我们可以通过用该标准碱滴定已知浓度的酸，同时监测 pH 值，来确定该酸的 pKa。以 pH 值对加入的碱体积作图，所得曲线称为滴定曲线。该曲线通常呈 S 形或称作sigmoidal形状，曲线上最陡部分的拐点即为等当点。
此时，氢氧根离子与解离的氢离子的摩尔数相等。与 pKa 相似，每种解离的氢离子都会对应一个当量点。因此，一元酸只有一个当量点，而三元酸则有三个当量点。
进行滴定时，当 pH 指示剂刚刚由无色变为微粉红色时，即表明已超过等当点。这被称为滴定终点。与标定碱液时类似，此时溶液中含有少量过量的氢氧根离子，因而呈弱碱性。
在滴定曲线中，另一个拐点出现在达到当量点一半的位置。在此处，解离酸与未解离酸的浓度相等，因此该点的 pH 值等于 pKa。因此，如果我们进行滴定并确定当量点所对应的体积，则可通过该体积一半时的 pH 值来计算 pKa。
在本实验中，您将首先标定您的碱溶液，然后使用已标定的碱溶液进行滴定，以确定一种多质子酸的两个 pKa 值。

酸和碱的浓度

<h4>酸和碱</h4>
阿伦尼乌斯酸在水中溶解时会产生氢离子：
HA + H2O → H+(aq) + A-(aq)
此处，HA 是未解离的酸，H+ 是氢阳离子，A- 是溶剂化的阴离子——称为共轭碱。阿伦尼乌斯碱在水中溶解时会产生氢氧根离子：
BOH + H2O → B+(aq) + OH-(aq)
此处，BOH 是未解离的碱，OH- 是氢氧根离子，B+ 是溶剂化的阳离子——称为共轭酸。当酸失去一个氢离子后形成的物质称为共轭碱，其具有重新获得氢离子的潜力。同理，当碱失去一个羟基后形成的物质称为共轭酸，其具有重新获得羟基的潜力。每种酸都有其对应的共轭碱，每种碱都有其对应的共轭酸。
<h4>pH</h4>
pH 是溶液酸性的程度，用于衡量溶液中氢离子的含量。pH 值呈对数关系，范围从 0 到 14；pH 低于 7 的水溶液称为酸性，pH 高于 7 的水溶液称为碱性或碱性。pH 为 7 的溶液被视为中性。
溶液的 pH 值等于溶液中氢离子浓度以 10 为底的负对数。
<img src="/CDNSource/lm/labs/44/44_Concepts_3.jpg" alt="pH 计算公式，pH = -log[H+]，化学酸度计算，化学教育概念。" data-altupdatedat="1761830439000" />
水与氢离子之间存在强烈的相互作用，因为氢离子的强正电荷会吸引周围水分子的负极。事实上，它们之间的相互作用非常强，以至于形成共价键，并生成称为水合氢离子的 H3O+ 阳离子。上述方程式被重写以反映这一过程。
<img src="/CDNSource/lm/labs/44/44_Concepts_4.jpg" alt="pH 计算公式，pH = -log10[H3O+]，化学平衡概念，用于教学。" data-altupdatedat="1761830439000" />
为简便起见，在讨论 pH 时，我们将使用氢离子浓度而非水合氢离子浓度。溶液的 pH 值越低，所含的氢离子越多，相应地，其酸性也越强。例如，1 mM 硫酸溶液的 pH 值为 2.75，而 1 mM 盐酸溶液的 pH 值为 3.01。硫酸溶液中氢离子浓度计算为 1 × 10-2.75，而盐酸溶液中氢离子浓度为 1 × 10-3.01。因此，硫酸溶液中氢离子更多，酸性更强。需要注意的是，即使两种溶液的 pH 值仅相差不到一个单位（例如仅相差 0.5），但由于 pH 值为对数尺度，其氢离子浓度的差异实际上非常显著。
<h4>酸和碱的强度</h4>
酸的强度受其共轭碱的电负性和酸性氢原子极性的影响。因此，酸的强度指的是氢阳离子（H+）从阴离子中解离的难易程度。强酸和强碱在水溶液中完全解离，而弱酸和弱碱仅部分解离为其共轭离子。
解离常数 Ka 代表酸的强度。Ka 通过未解离酸 HA 的浓度以及氢阳离子和共轭碱 A- 的浓度来计算。较高的 Ka 值代表较强的酸，而较低的 Ka 值代表较弱的酸。
<img src="/CDNSource/lm/labs/44/44_Concepts_5.jpg" alt="酸解离常数公式，化学分析中的Ka平衡方程。" data-altupdatedat="1761830439000" />
Ka 数值上非常小，通常以 pK 的形式报告a，即 K 的以 10 为底的负对数a较低的pKa 值对应较强的酸，而较高的 pKa 数值对应于较弱的酸。
<img src="/CDNSource/lm/labs/44/44_Concepts_6.jpg" alt="pKa 计算公式：pKa = -log10 Ka；酸解离常数分析方程。" data-altupdatedat="1761830439000" />
一些酸仅解离一个氢离子，因此只有一个 pKa 值，这类酸称为一元酸。然而，有些酸能够解离多个氢离子，被称为多元酸。这些酸对每个氢离子的解离都有一个对应的 pKa 值。
pKa 还可用于计算酸碱反应的平衡 pH 值，如 Henderson-Hasselbalch 方程所示。
<img src="/CDNSource/lm/labs/44/44_Concepts_7.jpg" alt="缓冲溶液的亨德森-哈塞尔巴尔赫方程、pH 计算、化学公式。" data-altupdatedat="1761830439000" />
当已知共轭碱和弱酸的浓度时，可使用 Henderson-Hasselbalch 方程计算 pH；或者当已知 pH 及浓度时，可用于计算 pKa。
<h4>滴定</h4>
酸碱反应可通过滴定进行定量研究。在滴定实验中，使用已知浓度的溶液（称为标准溶液）来测定另一种溶液的浓度。对于酸碱滴定，将已知浓度的碱标准溶液缓慢加入到未知浓度的酸溶液中（或反之，将酸加入到碱中）。该酸碱反应是一种中和反应，生成盐和水。当酸中氢离子的物质的量与碱中加入的氢氧根离子的物质的量相等时，溶液达到中性 pH 值。
进行酸碱滴定时，使用滴定管将已标定的碱液逐滴加入盛有未知浓度酸液并正在搅拌的锥形瓶中，滴定管可用于精确测量加入碱液的体积并实现逐滴添加。在整个滴定过程中，通过向酸液中加入 pH 指示剂来持续监测溶液的 pH 值。通常使用酚酞作为指示剂，因其在酸性条件下无色，当溶液变为碱性时则呈现淡粉色。
当滴定接近当量点时，即氢离子的物质的量等于所加入的羟基离子的物质的量时，由于羟基离子过量，pH 指示剂会暂时变色。当摇动锥形瓶后，pH 指示剂会恢复为酸性条件下的颜色。当出现极微量的羟基离子过量，并使指示剂永久变为其碱性颜色时，滴定完成，达到终点。
滴定曲线是溶液 pH 值随加入的标准碱液体积变化的关系图。等当点位于曲线的拐点处，并通过滴定曲线的二阶导数计算确定。
如果一种酸是多元酸，它将有多个化学计量点，每个氢离子解离对应一个化学计量点。对于一元酸，其滴定曲线中化学计量点一半位置处的 pH 值等于该酸的 pKₐ；对于多元酸，则在相邻两个化学计量点之间的中点处，pH 值等于相应的 pKₐ。a 酸的
<h4>参考文献</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). 化学与化学反应性。加利福尼亚州贝尔蒙特：Brooks/Cole, Cengage Learning。</li>
	<li style="font-size:17px">Silberberg, M.S. (2009). 化学：物质的分子本质与变化。马萨诸塞州波士顿：McGraw-Hill。</li>
	<li style="font-size:17px">Harris, D.C. (2015). 定量化学分析。纽约州纽约市：W.H. Freeman and Company。</li>
</ol>

酸和碱  
阿伦尼乌斯酸在水中溶解时产生氢离子：  
HA + H₂O → H⁺(aq) + A⁻(aq)  
此处，HA 为未解离的……

Education

教育

JoVE Lab Manual

化学

酸和碱浓度

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 and is logarithmic, so small changes in pH can mean large changes in hydrogen ion concentration. Solutions below pH 7 are acidic, solutions above pH 7 are basic or alkaline, and solutions at pH 7 are neutral. Water strongly attracts hydrogen ions and forms hydronium, H3O+, but pH is often discussed using hydrogen ion concentration for simplicity.

Lower pH means more hydrogen ions and greater acidity. For example, 1 mM sulfuric acid has a pH of 2.75, while 1 mM hydrochloric acid has a pH of 3.01. Because the pH scale is logarithmic, even a difference of about half a pH unit can reflect a large difference in hydrogen ion amount. In this example, sulfuric acid is more acidic because it contains more hydrogen ions.

Acid and base strength describes how readily hydrogen ions separate from the anion. Strong acids and bases dissociate completely in water, while weak acids and bases dissociate only partly into their conjugate ions. Acid strength is measured with the dissociation constant, Ka, which uses the concentrations of the non-dissociated acid HA, hydrogen cations, and conjugate base A-. Larger Ka values indicate stronger acids, and smaller values indicate weaker acids. Ka is often written as pKa, the negative base-10 log of Ka, so lower pKa means a stronger acid and higher pKa means a weaker acid.

Some acids release only one hydrogen ion, so they have one pKa and are called monoprotic. Others release more than one hydrogen ion and are polyprotic, with a pKa value for each step. The Henderson-Hasselbalch equation uses pKa to find the equilibrium pH of an acid-base reaction when the weak acid and conjugate base concentrations are known, or to find pKa when pH and concentrations are known.

Acid-base reactions can also be studied by titration. In a titration, a standard solution with a known concentration is used to find the concentration of another solution. For acid-base titrations, a standardized base is added slowly to an unknown acid, or the acid is added to the base. The reaction is a neutralization reaction that produces salt and water. When the moles of hydrogen ions match the moles of hydroxyl ions added, the solution reaches neutral pH.

During the experiment, the standardized base is added drop by drop from a burette to a stirring flask of acid. The pH is monitored with an indicator such as phenolphthalein, which stays colorless until the solution turns basic and becomes light pink. Near the equivalence point, the indicator may change color because of a temporary excess of hydroxyl ions, but swirling can return its acidic color. The endpoint is reached when a tiny extra amount of hydroxyl ions makes the basic color stay permanent.

A titration curve plots pH against the volume of standardized base added. The equivalence point appears at the inflection point of the curve and is found from the second derivative. Polyprotic acids have multiple equivalence points, one for each hydrogen ion dissociation. For monoprotic acids, the pH halfway to the equivalence point, or between equivalence points for polyprotic acids, is equal to the pKa.

Acids, Bases, and pH in Titration

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 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

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

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 acids, bases, pH, Ka, and pKa connect to titration, neutralization, and titration curves in high school chemistry.

Acids, Bases, and pH in Titration | JoVE K12

new-york-state-science-learning-standards

New York State Science Learning Standards

High School

Physical Science

HS. Chemical Reactions

HS-PS1-11.

Georgia Standards of Excellence

SC3.

Indicators of Chemical Reactions

SC6.

Neutralization Reactions

通过这段 5 分钟的教师指南，准备教授 酸和碱的浓度。涵盖 JoVE Lab Manual 上 Chemistry 实验的关键准备步骤。

Chemistry 中的 酸和碱的浓度 教师准备 - 6.2K+ 观看次数 | JoVE Lab Manual

在这段 15 分钟的学生实验流程视频中，逐步学习 酸和碱的浓度 的操作步骤。属于 JoVE Lab Manual 上的 Chemistry 系列。

Chemistry 中的 酸和碱的浓度 学生实验流程 - 31K+ 观看次数 | JoVE Lab Manual

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Matter and Its Interactions: Plan and conduct an investigation of acid-base reactions to test ideas about the concentrations of the hydronium ion in an aqueous solution (pH). (P:3, CC: 3, CI: PS1)

9C.1.2.1.2

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

Acids and Bases
An Arrhenius acid produces hydrogen ions when it is dissolved in water:
HA + H2O &#8594; H+(aq) + A-(aq)
Here, HA is the non-dissociated ...

Strong Acid and Base Solutions

A strong acid is a compound that dissociates completely in an aqueous solution and produces a concentration of hydronium ions equal to the initial ...

Polyprotic Acids

Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ...

Water: A Bronsted-Lowry Acid and Base

The reaction between a Br&#248;nsted-Lowry acid and water is called acid ionization. For example, when hydrogen fluoride dissolves in water and ionizes, ...

Weak Base Solutions

Some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and ...

Weak Acid Solutions

Few compounds act as strong acids. A far greater number of compounds behave as weak acids and only partially react with water, leaving a large majority of ...

The potential of hydrogen (pH) is a measure of the acidity or basicity of a water-based solution determined by the concentration of hydronium ions (H3O+). ...

water-quality-analysis-via-indicator-organisms

Water Quality Analysis via Indicator Organisms

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba -The University of Arizona
Demonstrating Author: Luisa Ikner
Water quality analysis monitors ...

Matter and Its Interactions: Obtain and communicate information about how Minnesota American Indian Tribes and communities and other cultures construct solutions to mitigate threats to biodiversity.* (P: 8, CC: 7, CI: LS2, ETS1)

1 Exploring phenomena or engineering problems
 1.2 Planning and carrying out investigations
  1.2.1 Students will be able to design and conduct investigations in the classroom, laboratory, and/or field to test students’ ideas and questions and will organize and collect data to provide evidence to support claims the students make about phenomena.

Acids, Bases, and pH in Titration

Description

Transcript

Tags

More videos by Standards