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

데이터 포인트의 실험 결과를 그래프와 같은 시각적 표현으로 변환하는 것은 둘 이상의 속성 간의 관계를 결정하는 데 필수적입니다. 이러한 속성을 변수라고 합니다. 변수가 두 개인 경우 데이터에서 생성된 그래프를 2차원이라고 합니다. 그래프에는 두 개의 축이 있습니다. 독립 변수는 x축에 표시되고 종속 변수는 y축에 그려집니다.
예를 들어, 가스의 온도와 부피에 대한 이 샘플 데이터를 생각해 보십시오. 가스의 부피는 온도에 따라 다릅니다. 따라서 측정된 온도를 x축에 표시하고 부피를 y축에 표시합니다.
한 온도에서 부피를 여러 번 측정한 경우와 같이 동일한 x-값을 가진 여러 데이터 포인트가 있는 경우 해당 측정값의 표준 편차도 계산합니다. 표준 편차는 통계 값으로, 값 집합에 존재하는 변동의 양을 나타냅니다.
표준 편차는 이 공식을 사용하여 계산되며, 여기서 n은 데이터 포인트의 수, x bar는 데이터 포인트의 평균값, xi는 각 개별 데이터 포인트를 나타냅니다. 표준 편차는 직접 계산하거나 스프레드시트 프로그램에서 자동으로 계산할 수 있습니다. 표준 편차가 0에 가까울수록 데이터 점이 평균값에 더 가깝습니다. 표준 편차가 0이면 입력된 모든 데이터 포인트가 동일한 값을 갖습니다.
데이터 세트의 각 온도에서 부피 측정의 평균값과 표준 편차를 살펴보겠습니다. 각 데이터 포인트 집합을 평균에 표준 편차를 더하거나 뺀 값으로 요약할 수 있습니다. 해당 측정에서 각 평균에 대한 유효 숫자를 결정하고 그에 따라 평균 값을 반올림합니다.
각 그룹의 표준 편차는 평균과 소수점 이하 자릿수가 같아야 하므로 각 표준 편차를 100분의 1 자리로 반올림합니다. 두 변수 간의 관계를 그래픽으로 결정하기 위해 최적 맞춤 함수로 데이터를 맞출 수 있습니다.
이 함수는 스프레드시트 소프트웨어에 의해 자동으로 생성되며 선형 추세선, 다항식 함수 또는 지수 또는 로그 함수의 형태를 취할 수 있습니다. 온도 및 부피 데이터의 경우 관계는 선형 관계입니다. 따라서 데이터 포인트는 선형 최소 제곱 회귀에 의해 적합합니다. 스프레드시트 프로그램은 최적선과 r-제곱 값에 대한 방정식을 반환합니다. r-제곱 값이 1에 가까울수록 데이터의 적합도가 더 좋습니다.
다음으로, 스프레드시트 소프트웨어를 사용하여 기울기의 표준 편차, y절편 및 계산된 y-값을 찾을 수 있습니다. 방정식의 값에 대한 유효 숫자를 결정하기 위해 간단한 규칙을 따릅니다. 각 값의 마지막 유효 숫자는 표준 편차의 첫 번째 유효 소수점 이하 자릿수에 해당합니다.
따라서 경사면을 1,000분의 1 자리로, y절편을 10분의 1 자리로 반올림한 다음 표준 편차를 반올림하여 일치시킵니다. 기울기는 켈빈당 0.167 +/- 0.003리터이고 y절편은 -40.6 +/- 1.2리터입니다. 계산된 모든 y 값은 10분의 1 자리로 반올림되며 +/- 0.8리터가 됩니다. 이 방정식은 온도와 기체 부피 사이의 관계를 설명합니다.
이 실습에서는 다양한 크기의 비커의 직경과 둘레를 측정하여 종속 변수와 독립 변수의 데이터 세트를 만듭니다. 그런 다음 이 데이터를 사용하여 산점도를 만들고 유효 숫자의 중요성을 염두에 두고 선형 회귀를 수행합니다. 또한 피펫을 사용하여 부피를 필터링하고 측정하는 것과 같은 실험실 기술을 연습하고 측정 및 분석의 불확실성에 주의를 기울이게 됩니다.

과학적 측정 및 실험실 기술

2차원 그래프
일부 화학 실험은 온도와 같은 독립 변수라고도 하는 연구 중인 시스템의 한 속성을 직접 변경하고 부피와 같은 종속 변수라고도 하는 다른 속성에 대한 영향을 측정하는 형태를 취합니다. 데이터가 수집되면 두 매개 변수 간의 상호 작용을 정량화하거나 평가할 수 있는 형식으로 변환하여 다른 관계와 비교해야 합니다.
2차원 그래프는 두 속성 간에 특정 유형의 수학적 관계를 도출하거나 두 속성 사이에 이러한 관계가 존재하지 않음을 확인하는 데 사용할 수 있습니다. 분석은 궁극적으로 종속 변수가 독립 변수에 대한 반응으로 어떻게 변경되는지를 결정합니다. 액체 또는 기체의 온도를 조정하고 부피의 변화를 모니터링하는 예에서 온도는 독립 변수이고 부피는 종속 변수입니다.
2차원 그래프를 만들려면 각 데이터 포인트에 종속 변수와 독립 변수 모두에 대한 좌표라는 값이 있어야 합니다. 독립 변수는 x축에 표시되고 종속 변수는 y축에 그려집니다. 이러한 플롯은 스프레드시트 소프트웨어에서 쉽게 만들 수 있으며 플롯된 데이터를 분석하는 데에도 사용할 수 있습니다.
곡선 피팅
데이터 세트가 2차원 그래프에 그려지면 곡선 피팅을 사용하여 독립 변수 측면에서 종속 변수에 대한 방정식 또는 함수를 생성할 수 있습니다. 함수는 파생된 데이터를 가장 잘 모델링하는 수학적 모델을 나타냅니다. 곡선 피팅은 데이터 포인트의 패턴과 잘 일치하는 선을 생성하는 함수를 찾는 기술입니다. 스프레드시트 소프트웨어에는 '최적'이라고 하는 다양한 곡선 맞춤 도구가 있습니다. 이것은 일반적으로 선형 최소제곱 회귀 분석이지만 대부분의 소프트웨어는 비선형 최소제곱 회귀도 제공합니다.
최적 선형 방정식의 정밀도는 데이터 포인트에 대한 x 값을 연결하고 방정식의 '이론적' 결과를 데이터 포인트의 실제 y 값과 비교하여 확인할 수 있습니다. 스프레드시트 소프트웨어는 일반적으로 함수의 결정 계수(R2) 값을 계산하며, 이는 함수가 데이터 포인트와 얼마나 잘 일치하는지를 보여줍니다. R2 값이 1에 가까울수록 선형 회귀에 더 잘 맞습니다. 다른 함수에는 함수가 데이터에 얼마나 잘 맞는지 확인하기 위해 보다 전문화된 방법이 있습니다.
최적 맞춤 함수에서 계산된 종속 값의 불확실성을 결정하려면 복잡한 "오류 전파" 기술이 필요합니다. 그러나 방정식 내의 불확실성을 최적 함수의 기울기와 y절편 모두에 대한 표준 편차의 형태로 계산할 수 있습니다. 이 작업은 일반적으로 2차원 플롯을 생성하는 데 사용되는 도구가 아닌 다른 도구를 사용하여 수행됩니다.
표준 편차
표준 편차는 값 집합에 존재하는 변동의 양을 설명합니다. 모집단 표준 편차(σ)는 유한한 모집단의 각 구성원의 데이터(예: 구슬 봉지에 있는 각 구슬의 질량)가 있을 때 사용됩니다. 표본 표준 편차는 다른 모든 경우에 사용되며 스프레드시트 소프트웨어의 기본 표준 편차 계산입니다. 1 '표준 편차'가 표본 표준 편차를 나타낸다고 가정할 수 있습니다.
무작위 측정 오류는 대략적으로 '정규' 분포를 따르는 것으로 가정되며, 값 집합의 약 68%가 평균의 양쪽에서 1 표준 편차 범위 내에 있고, 값의 95%가 평균의 양쪽에서 2 표준 편차 내에 있으며, 값의 99.7%가 평균의 양쪽에서 3 표준 편차 내에 있습니다. 따라서 표준 편차는 오류와 불확실성을 설명하는 유용한 방법입니다.
표본 표준 편차에 대한 방정식은 다음과 같습니다.
<img src="/CDNSource/lm/labs/42/42_Concepts_1.jpg">
이 방정식에서 N은 값의 수입니다. <img src="/CDNSource/lm/labs/42/30034eq02.jpg">는 값의 평균(또는 평균)이고 xi는 각 개별 값을 나타냅니다. 따라서 표준 편차를 직접 계산하려면 값 집합의 평균을 계산하고, 각 값에서 평균을 빼고, 각 차이를 제곱하고, 제곱 차이를 더하고, 총 합계를 값 수보다 1 작게 나누고, 몫의 제곱근을 취합니다. s가 0에 가까울수록 값 사이의 변동이 적습니다. 값이 스프레드시트 소프트웨어에 입력되면 소프트웨어 내에서 표준 편차를 계산할 수 있습니다.
표준 편차의 유효 숫자의 수는 그것이 어떤 값을 위한 것인지에 따라 다릅니다. 동일한 조건에서 수집된 데이터 포인트 그룹에 대한 표준 편차를 보고할 때 평균값에서 적절한 유효 숫자의 수를 먼저 결정해야 합니다. 그런 다음 표준 편차는 평균과 동일한 소수점 이하 자릿수로 반올림됩니다. 유효 숫자가 4개이고 평균이 15.361mL이며 표준 편차가 0.2313인 부피 세트의 경우 평균 및 표준 편차는 15.36mL ± 0.23mL로 보고됩니다.
스프레드시트 소프트웨어의 일반적인 방법인 최소제곱 분석에 의해 결정된 최적 함수에 대한 평균 및 y절편의 표준 편차를 보고할 때 표준 편차의 소수점 첫째 자리는 평균 또는 y절편의 마지막 유효 숫자입니다. 따라서 표준 편차는 하나의 중요한 소수점 이하 자리로 반올림해야 하고 기울기 또는 y-절편은 해당 소수점 이하 자리로 반올림해야 합니다. 예를 들어, 경사가 0.1691 L·K-1이고 표준 편차가 0.00512인 경우 경사는 0.169 L·K-1 ± 0.005 L·K-1로 보고되어야 합니다.
기울기 또는 y절편의 표준 편차가 해당 값보다 훨씬 작아 이 규칙을 따르면 원래 측정 데이터에서 허용하는 것보다 더 많은 기울기 또는 y절편에 더 많은 유효 수치를 제공할 수 있는 경우, 대신 x 및 y 값에서 기울기 또는 y절편의 유효 수치를 결정하고 표준 편차를 하나의 유효 숫자로 반올림합니다. 따라서 기울기 0.1691 L·K-1, 표준 편차 0.0000512, 유효 숫자 4개가 있는 x 및 y 값에 대해 기울기는 0.1691 L·K-1 ± 0.00005 L·K-1로 보고해야 합니다. 이 경우 계산된 값과 표준 편차가 소수점 이하 자릿수가 달라도 됩니다. 최소 제곱 방법은 x 값과 y 값을 모두 사용하여 기울기와 y절편을 계산한다는 점을 명심하십시오.
표준 편차를 불확실성 범위로 보고할 때는 불확실성이 1 표준 편차를 나타낸다는 점에 구체적으로 유의해야 합니다. 이것은 독자에게 정규 분포를 가정할 때 측정의 실제 값이 평균의 해당 범위 내에 속할 확률이 약 68%임을 알려줍니다. 불확실성을 평균에서 두 개의 표준 편차로 보고하는 것이 더 적합할 수 있으며, 이렇게 하면 확률이 약 95%로 증가합니다. 이렇게 하려면 적절한 유효 숫자 수로 반올림하기 전에 표준 편차에 2를 곱하기만 하면 됩니다.
참조
<ol :>
	<li style="font-size:17px">Harris, D.C. (2015). 정량적 화학 분석. 뉴욕, 뉴욕 : WH 프리먼 앤 컴퍼니.</li>
</ol>

2차원 그래프
일부 화학 실험은 연구하고있는 시스템의 한 속성을 직접 변경하는 형태를 취합니다.

Education

교육

JoVE Lab Manual

화학

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

화학 실험실에서 꼭 필요한 기본 커리큘럼 중심 비디오입니다.

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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

3분 길이의 강사용 가이드를 통해 과학적 측정 및 실험실 기술 수업을 준비하세요. JoVE Lab Manual의 Chemistry 실험을 위한 핵심 준비 단계를 다룹니다.

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15분 길이의 학생 프로토콜 영상을 통해 과학적 측정 및 실험실 기술 절차를 단계별로 따라 해보세요. JoVE Lab Manual의 Chemistry 컬렉션의 일부입니다.

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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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