Name: graphs, curve fit, and standard deviation
Uploaded: 2020-03-26T07:22:24.000Z
Duration: 4 min 34 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.1

CHEM.1.D

Scientific Measurement and Lab Skills

将实验结果从数据点转化为图形等可视化表示，对于确定两个或多个属性之间的关系至关重要。这些属性称为变量。当存在两个变量时，根据数据绘制的图形称为二维图。该图形具有两个坐标轴：自变量绘制在横轴（x轴）上，因变量绘制在纵轴（y轴）上。
以气体温度和体积的这组示例数据为例。气体的体积取决于温度。因此，我们将测量得到的温度绘制在 x 轴上，体积绘制在 y 轴上。
当多个数据点具有相同的 x 值时，例如在某一温度下多次测量体积，我们还需计算这些测量值的标准差。标准差是一个统计学数值，用于表示一组数值中变异程度的大小。
标准差使用此公式计算，其中 n 为数据点的数量，x̄ 为数据点的平均值，xi 表示每个单独的数据点。您可以手动计算标准差，也可以使用电子表格程序自动计算。标准差越接近 0，数据点越接近平均值。如果标准差等于 0，则所有输入的数据点具有相同的数值。
让我们查看数据集中每个温度下体积测量值的平均值和标准差。我们可以将每组数据点总结为平均值±标准差的形式。每个平均值的有效数字由相应的测量值确定，并据此对平均值进行修约。
每组的标准差必须与均值的小数位数相同，因此我们将每个标准差四舍五入至百分位。为了以图形方式确定两个变量之间的关系，我们可以使用最佳拟合函数对数据进行拟合。
该函数由电子表格软件自动生成，可以表现为线性趋势线、多项式函数，或指数函数、对数函数等形式。在本例的温度与体积数据中，二者关系呈线性，因此数据点通过线性最小二乘回归进行拟合。您的电子表格程序将返回最佳拟合直线的方程以及 r 平方值。r 平方值越接近 1，表示数据的拟合程度越好。
接下来，您可以使用电子表格软件计算斜率、y轴截距以及计算所得y值的标准偏差。为了确定方程中各数值的有效数字位数，我们遵循一个简单规则：每个数值的最后一位有效数字应与该数值标准偏差的第一个有效小数位相对应。
因此，我们将斜率保留至千分位，y轴截距保留至十分位，标准偏差也相应地进行四舍五入。斜率为 0.167 ± 0.003 升每开尔文，y轴截距为 -40.6 ± 1.2 升。任何计算得到的y值都将保留至十分位，误差为 ± 0.8 升。该方程描述了气体温度与体积之间的关系。
在本实验中，您将通过测量不同尺寸烧杯的直径和周长，建立一组自变量与因变量的数据集。然后，您将使用这些数据绘制散点图并进行线性回归分析，同时注意有效数字的重要性。您还将练习实验室技能，例如使用移液管进行过滤和体积测量，并关注测量与分析过程中的不确定性。

科学测量与实验技能

二维图
一些化学实验通过直接改变所研究体系的某一性质（即自变量，如温度），并测量其对另一性质（即因变量，如体积）的影响来进行。数据收集完成后，必须分析这两个参数之间的相互关系。 定量 — 或转化为可评估的形式，并与其他关系进行比较。
二维图形可用于推导两种性质之间的某些类型数学关系，或确定它们之间不存在此类关系。分析最终将确定因变量如何随自变量的变化而变化。例如，在调节液体或气体温度并监测其体积变化时，温度是自变量，体积是因变量。
绘制二维图形时，每个数据点必须具有一个称为坐标值的数值，分别对应因变量和自变量。自变量绘制在横轴（x轴）上，因变量绘制在纵轴（y轴）上。这些图形可方便地通过电子表格软件绘制，该软件还可用于分析已绘制的数据。
曲线拟合
将数据集绘制在二维图上后，可通过曲线拟合为因变量相对于自变量生成一个方程，即 函数。该函数代表了最能描述其来源数据的数学模型。曲线拟合是一种寻找函数的方法，使其生成的曲线与数据点的分布模式高度吻合。电子表格软件通常提供多种曲线拟合工具，称为“最佳拟合”。这通常采用线性最小二乘回归分析，但大多数软件也提供非线性最小二乘回归。
可以通过代入数据点的 x 值，将最佳拟合线性方程的“理论”结果与数据点的实际 y 值进行比较，从而检验该方程的精确度。电子表格软件通常会计算函数的决定系数（R2）值，该值反映了函数与数据点的吻合程度。R2 值越接近 1，线性回归的拟合效果越好。其他函数则有更专门的方法来判断函数对数据的拟合优度。
确定由最佳拟合函数计算出的因变量值的不确定性，需要使用复杂的“误差传递”技术。然而，可以通过计算最佳拟合函数斜率和 y 轴截距的标准差，来确定方程中的不确定性。这通常需要使用不同于生成二维图的工具来完成。
标准差
标准差用于描述一组数值中变异程度的大小。当数据来源于一个有限总体中的每个成员时，使用总体标准差（σ），例如一袋弹珠中每一颗弹珠的质量。在所有其他情况下均使用样本标准差（s），这也是电子表格软件中默认的标准差计算方式。1 除非特别说明，“标准差”通常指样本标准差。
随机测量误差通常被认为遵循近似“正态”分布，即约68%的数据值落在均值左右一个标准差的范围内，95%的数据值落在均值左右两个标准差的范围内，99.7%的数据值落在均值左右三个标准差的范围内。因此，标准差是描述误差和不确定性的有效方法。
样本标准差的计算公式为：
<img src="/CDNSource/lm/labs/42/42_Concepts_1.jpg" alt="标准差公式，统计方程，方差计算，描述性统计。" data-altupdatedat="1761830439000" />
在此方程中，N 为数值的个数； <img src="/CDNSource/lm/labs/42/30034eq02.jpg" alt="mean value symbol in statistical equation, relevant for data analysis and interpretation" data-altupdatedat="1761830439000" /> 是各数值的平均值（或均值）；以及 xi 表示每个单独的数值。因此，手动计算标准差时，需先计算这组数值的平均值，用每个数值减去平均值，将所得差值平方，再将所有平方差相加，将总和除以数值个数减一，最后对所得商取平方根。数值越接近 s 为零时，数值间的变异程度越小。若将数值输入电子表格软件，可直接在软件中计算标准差。
标准差的有效数字位数取决于其所对应的数据。当报告在相同条件下测得的一组数据点的标准差时，应首先确定平均值的适当有效数字位数，然后将标准差修约至与平均值相同的小数位数。例如，对于一组具有四位有效数字的体积数据，若其平均值为 15.361 mL，标准差为 0.2313，则平均值和标准差应报告为 15.36 mL ± 0.23 mL。
在报告通过最小二乘法分析确定的最佳拟合函数的均值和截距的标准偏差时（这是电子表格软件通常采用的方法），标准偏差的第一位小数即为均值或截距的最后一位有效数字。因此，标准偏差应四舍五入至一位有效小数位，而斜率或截距也应相应地四舍五入到同一位小数。例如，若斜率为 0.1691 L·K-1，其标准偏差为 0.00512，则该斜率应表示为 0.169 L·K-1 ± 0.005 L·K-1。
如果斜率或 y 轴截距的标准偏差远小于其对应数值，以致按照此规则确定的有效数字位数超过了原始测量数据所允许的范围，则应根据 x 和 y 值来确定斜率或 y 轴截距的有效数字位数，并将标准偏差修约至一位有效数字。因此，对于一个斜率为 0.1691 L·K 的情况-1，标准偏差为0.0000512，且x和y值具有四位有效数字时，斜率应报告为0.1691 L·K-1 ± 0.00005 L·K-‍1在这种情况下，计算值与其标准偏差的小数位数可以不同。需要注意的是，最小二乘法利用x值和y值共同计算斜率和y轴截距。
以标准偏差表示不确定度范围时，务必明确指出该不确定度代表一个标准偏差。这表明在假设呈正态分布的前提下，测量值的真实值约有68%的概率落在该均值范围内。通常，以均值的两个标准偏差来报告不确定度可能更为合适，因为这可将概率提高至约95%。为此，只需在将标准偏差修约至适当有效数字之前，将其乘以2即可。
参考文献
<ol style="font-size:17px">
	<li style="font-size:17px">Harris, D.C. (2015). 定量化学分析. 纽约, 纽约: W.H. Freeman and Company.</li>
</ol>

二维图  
某些化学实验的形式是直接改变所研究系统的某一性质，这被称为……

Education

教育

JoVE Lab Manual

化学

科学测量和实验室技能

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 a coordinate for both variables. The independent variable is plotted on the x-axis, and the dependent variable is plotted on the y-axis. These plots are often made in spreadsheet software, which can also be used to analyze the data. This helps show how the dependent variable changes in response to the independent variable.

Once the data are plotted, curve fitting can turn the pattern into an equation, or function. A function is a mathematical model that best matches the data it comes from. Curve fitting looks for a line or curve that fits the data points well. In many cases, spreadsheet tools use a best-fit method based on linear least-squares regression, although nonlinear least-squares regression is also available in most software.

The quality of a best-fit line can be checked by comparing the x values in the equation with the actual y values from the data. Spreadsheet software usually reports the coefficient of determination, or R squared, which shows how well the function matches the plotted points. A value closer to 1 means a better fit for linear regression. Finding uncertainty for values calculated from the equation can be more complicated, but standard deviation can be used to describe the uncertainty in the slope and y-intercept of a best-fit line.

Standard deviation shows how much values vary in a set. Population standard deviation, written as sigma, is used when data are available for every member of a finite population, such as the mass of each marble in a bag. Sample standard deviation, written as s, is used in all other cases and is the default in spreadsheet software. For that reason, standard deviation usually means sample standard deviation. Random measurement error is assumed to follow a roughly normal distribution, where about 68% of values fall within one standard deviation of the mean, 95% fall within two, and 99.7% fall within three.

The sample standard deviation can also be calculated by hand. First find the mean. Then subtract the mean from each value, square each difference, add the squared differences, divide by one less than the number of values, and take the square root. The closer s is to zero, the less variation there is in the data. Spreadsheet software can also calculate standard deviation directly.

When reporting standard deviation, the number of significant figures depends on what it describes. For a group of measurements taken under the same conditions, the standard deviation is rounded to the same number of decimal places as the mean. For example, 15.361 mL with a standard deviation of 0.2313 should be reported as 15.36 mL ± 0.23 mL. When reporting the standard deviation of a slope or y-intercept from least-squares analysis, the first decimal place of the standard deviation becomes the last significant figure of the value. So 0.1691 L·K-1 with a standard deviation of 0.00512 is reported as 0.169 L·K-1 ± 0.005 L·K-1.

If the standard deviation is much smaller than the slope or y-intercept, this rule can give more significant figures than the original x and y data allow. In that case, use the significant figures from the data and round the standard deviation to one significant figure. For example, 0.1691 L·K-1 with a standard deviation of 0.0000512 and x and y values with four significant figures is reported as 0.1691 L·K-1 ± 0.00005 L·K-1. It is important to state whether the uncertainty represents one standard deviation. One standard deviation gives about a 68% chance that the true value lies within that range. Two standard deviations may be a better choice when a wider uncertainty range is needed, since that raises the chance to about 95%.

Graphs, Curve Fit, and Standard Deviation

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

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

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.

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Learn how to plot independent and dependent variables, use best-fit lines, and report standard deviation to describe uncertainty in science data.

Graphs, Curve Fit, and Standard Deviation | JoVE K12

通过这段 3 分钟的教师指南，准备教授 科学测量与实验技能。涵盖 JoVE Lab Manual 上 Chemistry 实验的关键准备步骤。

Chemistry 中的 科学测量与实验技能 教师准备 - 5.8K+ 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 科学测量与实验技能 的操作步骤。属于 JoVE Lab Manual 上的 Chemistry 系列。

Chemistry 中的 科学测量与实验技能 学生实验流程 - 20K+ 观看次数 | JoVE Lab Manual

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

The Scientific Method

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

CHEM.1.A

What is an Experiment?

An experiment is a planned activity carried out under controlled conditions. The purpose of an experiment is to investigate the relationship between two ...

Study Design in Statistics

A study design is a set of techniques that allow a researcher to collect and analyze data from different variables defined for a specific research ...

Observational Studies

Observational studies are a type of analytical study where researchers observe events without any interventions. In other words, the researcher does not ...

Experimental Designs

An experimental design is a systematic process that allows researchers to evaluate the relationship between dependent and independent variables. There are ...

Randomized Experiments

The randomization process involves assigning study participants randomly to experimental or control groups based on their probability of being equally ...

Crossover Experiments

Crossover experiments, also called the repeated-measurements design, is a study design in which all experimental units are exposed to all treatments in ...

Controls in Experiments

When conducting an experiment, it is crucial to have control to reduce bias and accurately measure the dependent variables. It also marks the results more ...

Bias

Bias refers to any tendency that prevents a question from being considered unprejudiced. In research, bias occurs when one outcome or answer is selected ...

Blinding

Blinding is a commonly used method of not telling participants which treatment a subject is receiving. Blinding is a critical part of a randomized control ...

CHEM.1.B

Proper Personal Protective Equipment

Robert M. Rioux &#38; William A Elliott, Pennsylvania State University, University Park, PA
Hazards are many and varied in the laboratory, but the right ...

Emergency Eyewash and Shower Stations

Robert M. Rioux, Pennsylvania State University, University Park, PA
The Occupational Safety and Health Administration (OSHA) mandates that an emergency ...

Electrical Safety

Robert M. Rioux &amp; Suprita Jharimune, Pennsylvania State University, University Park, PA
Among the many hazards present in the laboratory, electrical ...

Working with Centrifuges

Source: Robert M. Rioux &amp; Suprita Jharimune, Pennsylvania State University, University Park, PA
Earth's gravitational force is capable of separating ...

Working with Hot and Cold Sources

Source: Robert M. Rioux &amp; Suprita Jharimune, Pennsylvania State University, University Park, PA
Working with extreme temperatures, both high and low, ...

guidelines-in-case-of-a-laboratory-emergency

Guidelines in Case of a Laboratory Emergency

Robert M. Rioux &amp; Zhifeng Chen, Pennsylvania State University, University Park, PA
The most common laboratory emergencies include chemical spills, ...

chemical-storage-categories-hazards-and-compatibilities

Chemical Storage: Categories, Hazards And Compatibilities

Source: Robert M. Rioux &amp; Taslima A. Zaman, Pennsylvania State University, University Park, PA
While the use of various chemicals in experimental ...

Safe Handling of Mineral Acids

Source: Robert M. Rioux &#38; Taslima A. Zaman, Pennsylvania State University, University Park, PA
A mineral acid (or inorganic acid) is defined as a ...

Handling Chemical Spills

Source: Robert M. Rioux &#38; Taslima Zaman, Pennsylvania State University, University Park, PA
Since chemicals are commonly used for laboratory research ...

Proper Use of Autoclaves

Robert M. Rioux &amp; Zhifeng Chen, Pennsylvania State University, University Park, PA
Autoclaving is one of the most commonly used methods in the ...

Fume Hoods and Laminar Flow Cabinets

Robert M. Rioux &amp; William A. Elliott, Pennsylvania State University, University Park, PA
Fume hoods and laminar flow cabinets are engineering controls ...

handling-air-and-water-sensitive-chemicals-using-a-schlenk-line

Handling Air- and Water-Sensitive Chemicals Using a Schlenk Line

Robert M Rioux, Ajay Sathe, Zhifeng Chen, Pennsylvania State University, University Park, PA
The use of reagents sensitive to oxidation or moisture ...

proper-operation-of-vacuum-based-equipment

Proper Operation of Vacuum Based Equipment

Source: Robert M. Rioux, Ajay Sathe &#38; Zhifeng Chen, Pennsylvania State University, University Park, PA
Vacuum is required for a number of laboratory ...

Operating the Glovebox

Robert M Rioux, Ajay Sathe, Zhifeng Chen, Pennsylvania State University, University Park, PA 
A glovebox is an isolated enclosure that is designed to ...

operation-of-high-pressure-reactor-vessels

Operation of High-pressure Reactor Vessels

Robert M Rioux, Pennsylvania State University, University Park, PA
The use of gases in a synthetic chemistry laboratory is essential for carrying out a ...

CHEM.1.C

Lab Techniques

Measurement Accuracy
The ability to repeat an experiment and get the same results, or reproducibility, is essential in scientific research. However, ...

Two-Dimensional Graphs
Some chemistry experiments take the form of directly changing one property of the system that you are studying otherwise known as ...

Proper Lab Notebook Keeping

Organic Lab Notebook Keeping
Record keeping is a vital skill in science and organic chemistry labs. Without proper notes, descriptions, quantities, or ...

Basic Organic Chemistry Techniques

Glassware in Organic Chemistry
There are standard pieces of glassware that are used in the organic chemistry lab. Beakers and Erlenmeyer flasks are ...

Measurement: Standard Units

Every measurement provides three kinds of information: the size or magnitude of the measurement (a number), a standard of comparison for the measurement ...

Measurement: Derived Units

The International System of Units or SI system, by international agreement, has fixed measurement units for seven fundamental properties: length, mass, ...

uncertainty-in-measurement-accuracy-and-precision

Uncertainty in Measurement: Accuracy and Precision

Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to evaluate both the precision and the accuracy ...

uncertainty-in-measurement-reading-instruments

Uncertainty in Measurement: Reading Instruments

Counting is the type of measurement that is free from uncertainty, provided the number of objects being counted does not change during the process. Such ...

CHEM.1.E

Scientific and engineering practices. The student, for at least 40% of instructional time, asks questions, identifies problems, and plans and safely conducts classroom, laboratory, and field investigations to answer questions, explain phenomena, or design solutions using appropriate tools and models. The student is expected to:

Graphs, Curve Fit, and Standard Deviation

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