Name: measuring with accuracy in the lab
Uploaded: 2020-03-26T07:22:24.000Z
Duration: 4 min 14 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Specialised Topic in Science

112.51.c.1.

112.51.c.1.D.

Lab Techniques

在科学研究中，实验的可重复性极为重要。因此，通过使用实验记录本详细记录实验步骤，并结合规范的实验操作技术，有助于重现实验结果。
例如，像液体体积这样的简单测量必须使用适当的玻璃器皿以确保准确性。应始终使用容量瓶、量筒或移液管等容量玻璃器皿来测量体积。体积读数应以弯月面底部为准。
烧杯和锥形瓶上的体积刻度并不精确，仅可作为参考。在选择容量玻璃器皿时，应选用能够容纳所需体积的最小容器。容量玻璃器皿的校准方式分为“排出”或“容纳”两种。
标有“量出式”的容器经过校准，可提供标示的体积，但需注意倒出液体后器壁会残留少量液体。因此，不应试图移除残留液体，否则会导致倒出的液体体积超过所需量。标有“量入式”的玻璃器皿可容纳并准确提供标示体积的液体，但需要将残留液体完全倒出，以确保接收到全部体积的液体。
我们进行测量以获得真实值。然而，测量结果总会存在一定程度的不确定性和误差。测量值是我们对实际值的最佳估计，而实际值通常未知。误差是测量值与实际值之间的差异。测量不确定度描述了我们认为实际值可能落入的范围。在记录测量结果时，保持适当数量的有效数字非常重要。
有效数字是指测量中具有意义的数字。最后一位数字定义了不确定性的程度。除前导零和末尾零以外的所有数字均为有效数字；当末尾零前面有小数点时，这些末尾零也是有效的。
例如，在使用直尺测量长度时，我们看到长度至少为1英寸，但肯定不到2英寸。因此，第一位有效数字是1。下一个刻度线代表0.1英寸，同样也是有效数字。
1.1 英寸的测量值具有两位有效数字，表示不确定度位于十分位。然而，实际宽度介于两条刻度线之间，因此当长度记录为 1.15 英寸时，不确定度位于百分位。
使用测量值进行计算时，切记不要将计算结果保留到比原始测量值更高的精度。这些额外的数字并不具有有效意义，不应包含在内。例如，当计算边长为 1.15 的正方形面积时，我们注意到该长度具有三位有效数字，因此结果也应保留三位有效数字。
计算得到的面积1.3225平方英寸包含五位有效数字，这在计算中引入了原始测量中并不存在的精确性。因此，正确的面积应为1.32平方英寸。
在本实验中，您将通过测量鸡蛋的密度并在计算和记录中使用有效数字，练习正确的实验技能。此外，您还将练习实验记录本中的记录方法，并考察容量玻璃器皿测量的准确性。

实验技术

<h4>测量准确性</h4>
能够重复进行实验并获得相同结果，即可重复性，在科学研究中至关重要。然而，如果你不清楚自己是如何进行实验的，就不可能实现重复。因此，科学家会在实验记录本中详细记录其实验过程。这些记录包括所用每种材料的用量以及实验步骤的详细描述等重要信息。
天平和容量瓶或刻度玻璃器皿等设备用于测量实验所需的固体和液体化合物。每次测量的精确度受限于所使用的设备。具有数字读数的天平及其他设备会自动显示其可支持的最高精度数值。刻度玻璃器皿和尺子的精度取决于分度值，即最小刻度线间距所代表的量。
大多数液体在玻璃容器中的表面边缘会向上弯曲。这种弯曲的液体表面称为凹液面。当液体边缘向下弯曲时，则称为凸液面。在测量液体体积时，液体表面的参考点为凹液面的底部或凸液面的顶部。为了准确定位液面位置，读取液体体积时应从侧面与眼睛齐平的位置观察液体表面。从上方或下方观察液体会导致液面看起来比实际位置偏高或偏低。
当弯月面的参考点与量具或容量玻璃器皿上的刻度线对齐时，该器皿所容纳的液体体积即为该刻度所标示的体积。容量玻璃器皿专用于测量特定体积，因此仅有一条刻度线。而量具玻璃器皿则设计用于测量一系列不同体积，因此具有多条等间距标示的刻度线，即分度线。无论是量具还是容量玻璃器皿，其表面可能还标有制造商提供的有关其测量精度的附加信息。
<h4>校准与不确定性</h4>
制造商对设备进行校准，以确保测量结果在指定的不确定度范围内准确。例如，一台高精度分析天平的读数可精确到小数点后四位（0.0000 g），其不确定度为 ± 0.0001 g。读数为 0.0345 g 时，表示真实值介于 0.0344 g 与 0.0346 g 之间。
玻璃器皿上通常会印有其测量不确定度。为了准确记录体积测量值，必须同时考虑最小分度值和不确定度。例如，使用量程为100 mL、最小分度为1 mL、不确定度为±0.5 mL的量筒进行精确体积测量时，测量结果应记录到十分位（000.0 mL ± 0.5 mL）。如果弯月面的参考点位于两条刻度线之间，应估读十分位的数值；否则，该位记为0。由于温度会影响体积，因此玻璃器皿上会标明其标定温度。
玻璃器皿经校准后，其刻度要么 包含 （总胆固醇）或 递送 （TD）。当TC玻璃器皿装液至标线时，其所容纳的液体体积即为标示体积，但在将液体倒入其他容器时，会有少量液体残留。由于溶液浓度的准确性受溶液体积准确性的影响，因此常使用TC玻璃器皿配制溶液。容量瓶通常标定为“容纳”（to contain）。
“TD”玻璃器皿在液面达到标线时所容纳的液体体积略大于标称容量，但其仅能准确释放出标称的体积。因此，在使用“TD”玻璃器皿分装液体时，不应将其完全排空。此类玻璃器皿适用于将精确体积的液体转移至另一容器。通常情况下，刻度移液管和容量移液管均按“排放式”进行校准。
除非另有说明，一个数值的不确定度通常被认为与最后一位数字的量级相当。因此，如果测量的不确定度处于更大的量级，则尤其需要明确报告其不确定度。对于没有已知不确定度的直尺和量具玻璃器皿，不确定度通常估计为最小刻度的一半。不确定数字的确定依据是液面弯月面位于两个刻度线之间的位置。 
<h4>有效数字</h4>
有效数字是指一个数值中具有意义或对以适当精度表达该数值至关重要的数字。除前导零（0.001）、末尾的零（1,000）或科学计数法中的乘数（10x）外，所有其他数字均为有效数字。
前导零从不具有有效数字意义，因为可以通过将数字改写为科学记数法，或在使用国际单位制（SI）单位时改写为更小的单位来去除。例如，数值 0.00123 m 只有三位有效数字，因为它可以改写为 1.23 × 10-3 米或1.23毫米，且不丢失任何信息。请注意，同一国际单位制单位不同倍数之间的换算系数 不 影响有效数字的位数。
当末尾的零位于小数点前或后时，这些零是有效数字。例如，测量值 100.110 mL 有六位有效数字，而 100.0 mL 有四位有效数字。对于未写出小数点的数字，其末尾的零通常被视为无效数字，除非另有标注。在这些情况下，存在多种不同的标注有效零的方法，但为了避免歧义，建议将这些数值改写为科学记数法。如果测量值使用的是 SI 单位，可改用更大的单位表示。
测量的精确度限制了由其计算所得数值的精确度。一个计算值的有效数字位数与用于计算的测量值相同。 最少 在计算中使用的精确测量值或数值，其结果的有效数字位数需与测量精度相匹配。若结果的有效数字过多，则应按适当精度进行修约；若有效数字过少，则需补足有效位的尾随零以保持精度。当实验测得的数值（如摩尔质量、密度或某些单位换算因子）用于计算时，也必须考虑其有效数字位数。
计算值中的有效数字位数 不 受限于公式中的物理或数学常数，或实验中获取的数据点数量等精确数值。例如，计算球体体积的公式为 V = 4/3πr3计算体积的有效数字位数为 仅 受半径测量有效数字位数的影响 r. 4/3&#8201; 和 π 是常数，且 3 仅仅是一种数学运算的符号表示。
明确定义的换算系数也被视为常数。例如，1英寸被定义为精确等于25.4毫米；因此，换算后数值的有效数字位数仅取决于原始测量值。在进行单位换算时，务必确认换算系数是明确定义的数值还是实验测定值。
对于测量值的简单加减运算，我们使用有效数字运算法则来确定有效数字的位数。在此类情况下，结果的小数位数与小数位数最少的测量值相同，而不考虑有效数字的位数。因此，15,643.7 mL + 0.613 mL = 15,644.3 mL。
对于需要分解为多个小步骤求解的多步计算或复杂方程，应在中间结果中至少保留一位或两位无效数字。例如，在分别计算分数的分子和分母后再进行除法运算时，应在进行除法时保留分子和分母中的无效数字。这样做可以最小化舍入误差，即与将整个公式一次性输入计算器所得结果之间的差异。如果需要记录这些中间值，应注明哪些数字是无效的。
<h4>参考文献</h4>
Harris, D.C. (2015). 定量化学分析. 纽约, 纽约州: W.H. Freeman and Company.

测量准确性  
重复实验并获得相同结果的能力，即再现性，在科学研究中至关重要。然而，……

Education

教育

JoVE Lab Manual

Chemistry

化学

实验室技术

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 maximum precision they can support. For rulers and graduated glassware, precision depends on the increment, which is the smallest distance between two marks.

Liquid levels must also be read correctly. Most liquids curve upward at the edges in glass containers. This curved surface is called a concave meniscus. When the edges curve downward, it is called a convex meniscus. To measure volume, the reference point is the bottom of a concave meniscus or the top of a convex meniscus. The reading should be taken from the side at eye level. Looking from above or below can make the level seem higher or lower than it really is.

Graduated and volumetric glassware are designed for different jobs. Volumetric glassware measures one specific volume and has only one mark. Graduated glassware measures a range of volumes and has many marks, or graduations, at regular intervals. When the meniscus reference point touches the mark, the glassware is holding the volume defined by that mark. Both types may also include manufacturer information about precision.

Manufacturers calibrate equipment so measurements stay within a stated range of uncertainty. A high-precision analytical balance may read to four decimal places, such as 0.0000 g, with an uncertainty of ±0.0001 g. That means a reading of 0.0345 g could represent a true value between 0.0344 g and 0.0346 g. Glassware usually has its uncertainty printed on it. For a 100 mL graduated cylinder with 1 mL increments and an uncertainty of ±0.5 mL, the volume should be recorded to the tenths place.

Temperature also affects volume, so calibrated glassware lists the temperature it is made for. Glassware can be calibrated to contain, or TC, or to deliver, or TD. TC glassware holds the stated volume when filled to the mark, but some liquid remains after pouring. This is why volumetric flasks are usually TC and are often used to prepare solutions, since solution concentration depends on volume accuracy. TD glassware dispenses the stated volume and should not be emptied completely. Graduated and volumetric pipettes are typically TD and are useful for transferring an exact volume to another container.

Recording numbers correctly also requires understanding uncertainty and significant figures. Unless stated otherwise, uncertainty is assumed to be on the scale of the last digit. If a ruler or glassware has no known uncertainty, estimate it as half of the smallest increment. Significant figures are the digits that are meaningful for the precision of a value. Leading zeroes are not significant, while trailing zeroes are significant when they appear before or after a decimal point. A number written without a decimal point may need scientific notation to avoid ambiguity.

Calculated values must match the precision of the measurements used to find them. The result should have the same number of significant figures as the least precise value in the calculation. If the answer has too many significant figures, round it. If it has too few, add significant trailing zeroes to show the correct precision. Constants such as 4/3 and π in the sphere volume formula do not limit the number of significant figures, and exact conversion factors like 1 inch = 25.4 millimeters also do not. For addition and subtraction, the answer keeps the same number of decimal places as the least precise value. For multi-step problems, keep one or two extra digits during intermediate steps to reduce rounding error.

Measuring with Accuracy in the Lab

lab techniques

Measuring with accuracy in the lab starts with careful records, the right tools, and correct reading of data. Scientists use lab notebooks to record how an experiment was done. These notes include the amounts of materials used and each step of the procedure. Without that record, an experiment cannot be repeated in the same way. Balances and glassware are used to measure solids and liquids for experiments. The precision of a measurement depends on the equipment used. Digital balances show the...

scientific measurement and lab skills

Graphs, Curve Fit, and Standard Deviation

Two-dimensional graphs help students compare an independent variable with a dependent variable in science data. In a chemistry example, temperature is the independent variable and volume is the dependent variable. After data are collected, the relationship between the two measurements must be quantified so it can be evaluated and compared with other relationships. A graph can also show when no relationship exists between the two variables. To make a two-dimensional graph, each data point needs...

stoichiometry, product yield, and limiting reactants

stoichiometry-product-yield-and-limiting-reactants

Balancing Equations and Reactant Limits

Chemical equations show how reactants change into products during a reaction. Stoichiometry is the study of the relative amounts of reactants and products. It is based on the Law of Conservation of Mass, which says matter is neither created nor destroyed. Because atoms are only rearranged, the number and identity of atoms must match on both sides of a reaction. That is why a chemical equation must be balanced. A balanced equation has the same number of atoms for each element in the reactants...

redox reactions

Oxidation States in Redox Reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number. Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding...

ideal gas law

Gas Laws Behind the Ideal Gas Equation

The ideal gas equation brings together the main gas laws used in chemistry. Gases have molecules that are far apart, so their behavior is described with four measurable variables: pressure, volume, number of moles, and temperature. The ideal gas law links these variables with the gas constant, R, which equals 8.314 J·K−1 mol−1. Boyle’s law describes the link between pressure and volume. When temperature and the number of moles stay constant, pressure and volume change in opposite directions.

acid and base concentrations

Acids, Bases, and pH in Titration

Acids, bases, and pH explain how acidic or basic a solution is. An Arrhenius acid releases hydrogen ions when it dissolves in water, while an Arrhenius base releases hydroxide ions. These reactions also create conjugate partners: an acid forms a conjugate base after losing hydrogen, and a base forms a conjugate acid after losing hydroxyl. Every acid has a conjugate base, and every base has a conjugate acid. pH measures the amount of hydrogen ions in a solution. The pH scale runs from 0 to 14...

buffers

Buffer pH and the Common Ion Effect

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

enthalpy of reaction

Reaction Heat, Hess’s Law, and Calorimetry

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

solubility

Solubility in Water and Other Solvents

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

metal flame emission

Flame Test Metal Color Clues

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

balmer series

Hydrogen Emission Lines

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

beer's law

Absorbance Spectra and Beer-Lambert Analysis

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

concentration dependence

Reaction Order and Rate Constants

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

temperature dependence

Reaction Rate, Arrhenius, and Catalysts

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

galvanic cells

Battery Power from Redox Reactions

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

electrolytic cells

Electroplating with Electrolytic Cells

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

proper lab notebook keeping

Recording a Reproducible Lab Experiment

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

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

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

melting points

How Impurities Change Melting Points

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

boiling points

Boiling Point and Vapor Pressure

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

recrystallization

Purifying Crystals by Solubility

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

extraction

Separating Mixtures with Solvent Extraction

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

simple distillation

Separating Liquids by Boiling Point

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

steam distillation

Steam Distillation and Low-Boiling Separation

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

thin-layer chromatography

TLC Separation by Polarity

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

column chromatography

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 students measure liquids and solids, read meniscus levels, use TC and TD glassware, and apply uncertainty and significant figures.

Measuring with Accuracy in the Lab | JoVE K12

CHEM.1

CHEM.1.D

Biology

BIO.1

BIO.1.E

通过这段 1 分钟的教师指南，准备教授 实验室技术。涵盖 JoVE Lab Manual 上 Chemistry 实验的关键准备步骤。

Chemistry 中的 实验室技术 教师准备 - 9.8K+ 观看次数 | JoVE Lab Manual

在这段 9 分钟的学生实验流程视频中，逐步学习 实验技术 的操作步骤。属于 JoVE Lab Manual 上的 Chemistry 系列。

Chemistry 中的 实验技术 学生实验流程 - 30K+ 观看次数 | JoVE Lab Manual

The Scientific Method

The scientific method is a detailed, empirical problem-solving process used by biologists and other scientists. This iterative approach involves ...

Inductive Reasoning

Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. It is uncertain and operates in ...

Deductive Reasoning

Deductive reasoning, or deduction, is the type of logic used in hypothesis-based science. In deductive reasoning, the pattern of thinking moves in the ...

Correlation and Causation

Correlation and CausationStatistical tests can calculate whether there is a relationship, or correlation, between independent and dependent variables. A ...

Ask questions and define problems related to specialized topics of study based on observations or information from text, phenomena, models, or investigations;

112.51.c.1.A.

Scientific Method

The scientific method is used to solve problems and explain phenomena. The development of the scientific method coincided with changes in philosophy ...

Demonstrating the Scientific Method with Tree Branches
ExpandObtain branches containing a few dozen typical leaves from five different local tree species. ...

Observation and Background Research
ExpandNOTE: The first two steps in the scientific process involve studying and observing natural phenomena of ...

Problem-Solving

A problem-solving strategy is a plan of action used to find a solution. It involves trial and error, algorithms, heuristics, and insights. Effective ...

Problem Definition

Problem definition is the initial and the most essential step in research.
The researcher identifies and explains the specific issue or gap to be ...

Apply science practices related to specialized topics of study to plan and conduct investigations or use engineering practices to design solutions to problems;

112.51.c.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 ...

Decontamination for Laboratory Biosafety

Robert M. Rioux and Zhifeng Chen, Pennsylvania State University, University Park, PA
Decontamination is essential for laboratory biosafety, as the ...

Proper Waste Disposal

Robert M. Rioux and Taslima A. Zaman, Pennsylvania State University, Pennsylvania, PA

Users are responsible for the proper disposal of the waste ...

Use appropriate safety equipment and practices during laboratory, classroom, and field investigations as outlined in Texas Education Agency-approved safety standards;

112.51.c.1.C.

Common Lab Glassware and Uses

Source: Laboratory of Dr. Neal Abrams &#8212; SUNY College of Environmental Science and Forestry
Glassware is a regular appearance in the professional ...

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

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Preparation of LaboratoryExpand
	Here we show the laboratory preparation for 10 students ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Determining the Density of an EggExpand
	Density is a measure of how compact a substance or ...

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 ...

Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA

	Preparation of the LaboratoryExpand
	Here, we show the laboratory preparation ...

Source: Lara Al Hariri and Ahmed Basabrain at the University of Massachusetts Amherst, MA, USA

	Nitration of Methyl BenzoateExpand
	From this lab onward, ...

Use tools appropriate to the specialized topic of study;

SI Units: 2019 Redefinition

Measurement is integral to analytical chemistry. Each record comprises a number &#8211; denoting the magnitude&#160; &#8211; and the unit &#8211; a ...

International System of Units

The International System of Units, known as the SI system, is a universally accepted measurement system recognized and used worldwide. The SI system is ...

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, ...

Collect quantitative data using the International System of Units (SI) or qualitative data as evidence as appropriate to the specialized topic of study;

112.51.c.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 explain phenomena or design solutions using appropriate tools and models. The student is expected to:

Measuring with Accuracy in the Lab

Description

Transcript

More videos by Standards