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

과학 연구에서 실험의 재현성은 매우 중요합니다. 따라서 적절한 실험실 기술과 함께 자세한 절차 기록이 포함된 실험실 노트를 보관하면 실험 결과를 재현하는 데 도움이 됩니다.
예를 들어, 액체의 부피와 같은 간단한 측정은 정확성을 보장하기 위해 적절한 유리 기구를 사용하여 수행해야 합니다. 항상 부피 측정 플라스크, 눈금이 매겨진 실린더 또는 부피 측정 피펫과 같은 부피 측정 유리 기구를 사용하여 부피를 측정하십시오. 부피는 반월판 바닥에서 측정됩니다.
비커와 삼각 플라스크의 부피 표시는 정확하지 않으며 지침으로만 사용됩니다. 부피 측정 유리 용기를 선택할 때 필요한 부피에 대해 가능한 가장 작은 용기를 선택하십시오. 체적 유리 기구는 전달하거나 포함하기 위해 보정됩니다.
전달하도록 보정된 용기는 유리 제품을 비운 후 소량의 액체가 남아 있다는 이해를 바탕으로 명시된 부피를 제공하도록 설계되었습니다. 이 경우 남은 액체를 제거할 필요가 없거나 원하는 양보다 더 많이 비워집니다. 포함하도록 보정된 유리 용기는 명시된 부피를 유지하고 전달하지만 전체 부피를 받을 수 있도록 나머지 액체를 부어야 합니다.
우리는 진정한 값을 얻기 위해 측정합니다. 그러나 항상 어느 정도의 불확실성과 오류가 존재합니다. 측정된 값은 실제 값에 대한 최선의 추정치이며, 이는 종종 우리에게 알려지지 않습니다. 오류는 측정된 값과 실제 값의 차이입니다. 측정 불확도는 실제 값이 있을 가능성이 있다고 생각하는 범위를 설명합니다. 측정값을 기록할 때 적절한 수의 유효 숫자를 유지하는 것이 중요합니다.
유효 숫자는 의미를 전달하는 측정의 숫자입니다. 기록된 마지막 숫자는 불확실성의 수준을 정의합니다. 선행 0과 후행 0을 제외한 모든 숫자는 중요합니다. 그리고 후행 0은 앞에 소수점이 있을 때 중요합니다.
예를 들어, 자를 사용하여 길이를 측정할 때 길이가 최소 1인치이지만 확실히 2인치는 아님을 알 수 있습니다. 따라서 첫 번째 유효 숫자는 1입니다. 다음 눈금 표시는 0.1인치를 나타내며 이 또한 중요합니다.
1.1인치의 기록에는 두 개의 유효 숫자가 있으며 불확실성이 10분의 1에 있음을 의미합니다. 그러나 실제 너비는 두 눈금 사이에 있습니다. 따라서 길이가 1.15인치로 보고되기 때문에 불확실성은 100분의 1 자리에 있습니다.
측정값을 사용하여 계산을 수행할 때 원래 측정보다 높은 해상도로 계산을 수행하지 마십시오. 이러한 추가 숫자는 중요하지 않으므로 포함해서는 안 됩니다. 예를 들어, 한 변의 길이가 1.15인 정사각형의 면적을 계산할 때 길이에 세 개의 유효 숫자가 있음을 알 수 있습니다. 따라서 답에는 세 개의 유효 숫자도 있어야 합니다.
계산된 면적 1.3225인치 제곱에는 5개의 숫자가 있으며 원래 측정에는 없었던 계산에 확실성을 도입합니다. 따라서 올바른 면적은 1.32인치 제곱입니다.
이 실습에서는 난자의 밀도를 측정하고 계산 및 기록에 유효 숫자를 활용하여 적절한 실험실 기술을 연습합니다. 또한 실험실 노트에 기록 보관을 연습하고 체적 유리 기구로 측정의 정확도를 검사합니다.

실험실 기술

<h4>측정 정확도</h4>
실험을 반복하고 동일한 결과를 얻을 수 있는 능력 또는 재현성은 과학 연구에서 필수적입니다. 그러나 어떻게 했는지 모른다면 실험을 반복할 수 없습니다. 따라서 과학자들은 실험에 대한 자세한 기록을 실험실 노트에 보관합니다. 이러한 기록에는 사용된 각 재료의 양 및 절차의 각 단계에 대한 설명과 같은 중요한 정보가 포함됩니다.
저울 및 체적 또는 눈금이 매겨진 유리 기구와 같은 장비는 실험을 위한 고체 및 액체 화합물을 측정하는 데 사용됩니다. 각 측정의 정밀도는 사용되는 장비에 의해 제한됩니다. 저울 및 디지털 판독 기능이 있는 기타 장비는 지원할 수 있는 최대 정밀도로 값을 자동으로 표시합니다. 눈금이 매겨진 유리 제품과 눈금자의 정밀도는 두 마크 사이의 가장 작은 거리로 표시되는 양인 증가에 따라 달라집니다.
대부분의 액체의 표면은 유리 용기의 가장자리에서 위쪽으로 구부러져 있습니다. 이러한 유형의 곡선 액체 표면을 오목한 반월판이라고 합니다. 액체의 가장자리가 아래로 구부러지면 볼록한 반월판이라고 합니다. 액체의 부피를 측정할 때 액체 상단의 기준점은 오목한 메니스커스의 바닥 또는 볼록한 메니스커스의 상단입니다. 반월판의 위치를 정확하게 식별하기 위해 눈높이에서 측면에서 액체 표면을 보고 액체의 부피를 읽습니다. 위 또는 아래에서 액체를 보면 액체 표면 레벨이 실제보다 높거나 낮게 나타납니다.
메니스커스의 기준점이 눈금이 매겨진 유리 그릇 또는 부피 측정 유리 그릇의 표시에 닿을 때, 유리 그릇은 해당 기호에 대해 정의된 부피를 유지하고 있는 것입니다. 체적 유리 기구는 특정 부피를 측정하도록 설계되었으므로 표시가 하나만 있습니다. 눈금이 매겨진 유리 제품은 다양한 부피를 측정하도록 설계되었기 때문에 일정한 간격으로 레이블이 지정된 많은 표시 또는 눈금이 있습니다. 눈금이 매겨진 유리 제품과 부피 측정 유리 제품 모두 정밀도에 대한 추가 제조업체 제공 정보가있을 수 있습니다.
<h4>교정 및 불확도</h4>
제조업체는 지정된 불확도 범위 내에서 측정이 정확한지 확인하기 위해 장비를 보정합니다. 예를 들어, 고정밀 분석 저울은 ± 0.0001g의 불확도로 소수점 이하 네 자리(0.0000g)까지 판독할 수 있습니다. 0.0345g의 판독값은 실제 값이 0.0344g에서 0.0346g 사이임을 나타냅니다.
유리 제품에는 일반적으로 측정 불확실성이 인쇄되어 있습니다. 부피 측정값을 정확하게 기록하려면 증가와 불확실성을 모두 고려해야 합니다. 예를 들어, 100mL 눈금이 매겨진 실린더에서 1mL씩 증가하고 불확도가 0.5mL± 정밀하게 측정되면 10분의 1(000.0mL ± 0.5mL)까지 기록됩니다. 반월판의 기준점이 두 표시 사이에 있는 경우 10분의 1 자리에 대한 값을 추정해야 합니다. 그렇지 않으면 0으로 둡니다. 온도는 부피에 영향을 미치기 때문에 유리 제품이 보정되는 온도가 인쇄됩니다.
유리 제품은 포함(TC) 또는 전달(TD)하도록 보정됩니다. TC 유리 제품은 표시까지 채워질 때 지정된 양의 액체를 유지하지만 다른 용기에 부을 때 소량의 액체가 남습니다. 용액은 종종 TC 유리 용기에서 준비되는데, 이는 용액 부피의 정확도가 농도의 정확도에 영향을 미치기 때문입니다. 부피 측정 플라스크는 일반적으로 포함하도록 보정됩니다.
TD 유리 제품은 표시까지 채워질 때 지정된 액체의 양보다 약간 더 많은 액체를 담을 수 있지만 지정된 부피만 분배합니다. 따라서 액체를 분배할 때 TD 유리 제품을 완전히 비워서는 안 됩니다. 이러한 유형의 유리 제품은 정확한 양의 액체를 다른 용기로 옮기는 데 유용합니다. 눈금이 매겨진 피펫과 부피 측정 피펫은 모두 일반적으로 전달하도록 보정됩니다.
달리 명시되지 않는 한, 숫자의 불확실성은 마지막 숫자의 척도에 있는 것으로 가정합니다. 따라서 불확실성이 더 큰 척도인 경우 측정의 불확실성을 보고하는 것이 특히 중요합니다. 알려진 불확실성이 없는 눈금자 및 눈금이 매겨진 유리 제품의 경우 불확실성은 가장 작은 증가의 절반으로 추정됩니다. 불확실한 숫자는 두 눈금 표시 사이에 있는 반월판의 위치를 기반으로 합니다.
<h4>유효 숫자</h4>
유효 숫자는 의미 있거나 해당 값을 적절한 정밀도로 표현하는 데 필수적인 값의 숫자입니다. 선행 0(0.001), 후행 0(1,000) 또는 과학적 표기법 승수(10x)를 제외한 모든 숫자는 항상 중요합니다.
선행 0은 숫자를 과학적 표기법으로 다시 쓰거나 SI 단위인 경우 더 작은 단위로 다시 작성하여 제거할 수 있기 때문에 결코 중요하지 않습니다. 예를 들어, 0.00123m 값에는 정보 손실 없이 1.23 × 10-3m 또는 1.23mm로 다시 쓸 수 있기 때문에 유효 숫자가 세 개뿐입니다. 동일한 SI 단위의 서로 다른 배수 사이의 스케일링 계수는 유효 숫자의 수에 영향을 미치지 않습니다.
후행 0은 소수점 앞이나 뒤에 있을 때 중요합니다. 예를 들어, 100.110mL 측정값에는 6개의 유효 숫자가 있고 100.0mL에는 4개의 유효 숫자가 있습니다. 소수점 없이 쓰여진 숫자의 후행 0은 달리 표시되지 않는 한 중요하지 않은 것으로 간주됩니다. 이러한 경우 중요한 0을 표시하기 위한 몇 가지 다른 규칙이 있지만 모호성을 피하려면 해당 값을 과학적 표기법으로 다시 작성하는 것이 좋습니다. 측정값이 SI 단위인 경우 더 큰 단위를 사용합니다.
측정의 정밀도는 측정에서 계산된 모든 값의 정밀도를 제한합니다. 계산된 값에는 계산에 사용된 가장 덜 정확한 측정값 또는 값과 동일한 수의 유효 숫자가 있습니다. 결과에 유효 숫자가 너무 많으면 적절한 정밀도로 반올림됩니다. 결과에 유효 숫자가 너무 적으면 정밀도를 유지하기 위해 유효 후행 0으로 확장됩니다. 몰 질량, 밀도 또는 일부 단위 변환 계수와 같은 실험적으로 파생된 값의 유효 수치도 계산에 사용할 때 고려해야 합니다.
계산된 값에서 유효 숫자의 수는 공식의 물리적 또는 수학적 상수나 실험에서 획득한 데이터 포인트의 수와 같은 정확한 숫자에 의해 제한되지 않습니다. 예를 들어, 구의 부피를 계산하는 공식은 V = 4/3πr3입니다. 계산된 부피에서 유효 숫자의 수는 반경 측정 r의 유효 숫자의 수에 의해서만 영향을 받습니다. 4/3 및 π은 상수이고 3은 단순히 수학 연산에 대한 표기법입니다.
정의된 변환 계수도 상수로 처리됩니다. 예를 들어, 인치는 정확히 25.4mm로 정의됩니다. 따라서 변환된 값의 유효 숫자의 수는 원래 측정에만 의존합니다. 단위 간 변환 시 변환 계수가 정확하게 정의되었는지 또는 실험 값인지 항상 확인하십시오.
측정값의 간단한 덧셈과 뺄셈을 위해 유의성 산술을 사용하여 유효 숫자의 수를 결정합니다. 이 경우 답은 유효 숫자의 수에 관계없이 소수점 이하 자릿수가 가장 적은 측정값만큼 소수 자릿수를 갖습니다. 따라서 15,643.7 mL + 0.613 mL = 15,644.3 mL입니다.
풀기 위해 더 작은 부분으로 나누는 다단계 계산 또는 복잡한 방정식의 경우 중간 값에 하나 또는 두 개의 중요하지 않은 숫자를 유지해야 합니다. 예를 들어, 분수의 분자와 분모의 값을 나누기 전에 따로 계산하는 경우, 분자와 분모의 무의미한 숫자를 나눌 때 유지해야 합니다. 이렇게 하면 전체 수식을 계산기에 한 번에 입력했을 때 얻을 수 있는 숫자와의 차이인 반올림 오류가 최소화됩니다. 이러한 중간 값을 기록해 두면 어떤 숫자가 중요하지 않은지 기록해야 합니다.
<h4>참조</h4>
해리스, DC (2015). 정량적 화학 분석. 뉴욕, 뉴욕 : WH 프리먼 앤 컴퍼니.

측정 정확도
실험을 반복하고 동일한 결과를 얻을 수 있는 능력 또는 재현성은 과학 연구에서 필수적입니다. 그렇지만...

Education

교육

JoVE Lab Manual

Chemistry

화학

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

화학 실험실에서 꼭 필요한 기본 커리큘럼 중심 비디오입니다.

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

1분 길이의 강사용 가이드를 통해 실험실 기술 수업을 준비하세요. JoVE Lab Manual의 Chemistry 실험을 위한 핵심 준비 단계를 다룹니다.

Chemistry의 실험실 기술 강사용 준비 - 9.8K+ 조회수 | JoVE Lab Manual

9분 길이의 학생 프로토콜 영상을 통해 실험실 기술 절차를 단계별로 따라 해보세요. JoVE Lab Manual의 Chemistry 컬렉션의 일부입니다.

Chemistry의 실험실 기술 학생 프로토콜 - 30K+ 조회수 | 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.

Review and Preview

Data are individual items of information obtained from a population or sample. Data may be classified as qualitative (categorical), quantitative ...

Organize quantitative or qualitative data using representations appropriate to the specialized topic of study such as scatter plots, line graphs, bar graphs, charts, data tables, diagrams, scientific drawings, and student-prepared models;

112.51.c.1.F.

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