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

Nella ricerca scientifica, la riproducibilità di un esperimento è estremamente importante. Pertanto, tenere un quaderno di laboratorio con registrazioni procedurali dettagliate insieme a tecniche di laboratorio adeguate aiuta a riprodurre i risultati sperimentali.
Ad esempio, le misurazioni semplici, come il volume del liquido, devono essere eseguite utilizzando la vetreria adeguata per garantire l'accuratezza. Misurare sempre il volume utilizzando vetreria volumetrica, come un matraccio tarato, un cilindro graduato o una pipetta volumetrica. Il volume viene misurato nella parte inferiore del menisco.
Le marcature del volume sui becher e sui palloni di Erlenmeyer non sono accurate e servono solo come linee guida. Quando si seleziona la vetreria volumetrica, selezionare il contenitore più piccolo possibile per il volume necessario. La vetreria volumetrica è calibrata per erogare o per contenere.
I contenitori calibrati per l'erogazione sono progettati per fornire il volume dichiarato con la consapevolezza che una piccola quantità di liquido rimarrà nella vetreria dopo che è stata svuotata. In questo caso, non è necessario rimuovere il liquido rimanente o verrà svuotato più del volume desiderato. La vetreria calibrata per contenere manterrà ed erogherà il volume dichiarato, ma richiederà che il liquido rimanente venga versato in modo da ricevere l'intero volume.
Misuriamo per ottenere un valore reale. Tuttavia, ci sarà sempre un certo livello di incertezza ed errore. Il valore misurato è la nostra migliore stima del valore effettivo, che spesso ci è sconosciuto. L'errore è la differenza tra il valore misurato e quello effettivo. L'incertezza di misura descrive l'intervallo in cui riteniamo probabile che si trovi il valore effettivo. Quando si registrano le misurazioni, è importante mantenere il numero appropriato di cifre significative.
Le cifre significative sono le cifre di una misurazione che hanno un significato. L'ultima cifra registrata definisce il livello di incertezza. Tutti i numeri diversi dagli zeri iniziali e finali sono significativi. E gli zeri finali sono significativi quando c'è un punto decimale che li precede.
Ad esempio, in una misurazione della lunghezza utilizzando un righello, vediamo che la lunghezza è di almeno un pollice, ma certamente non di 2 pollici. Quindi, la prima cifra significativa è una. Il segno di spunta successivo rappresenta 0,1 pollici ed è anch'esso significativo.
Una registrazione di 1,1 pollici ha due cifre significative e implica che l'incertezza si trova al decimo posto. Tuttavia, la larghezza reale si trova tra due segni di graduazione. Quindi, l'incertezza risiede qui al centesimo posto poiché la lunghezza è riportata come 1,15 pollici.
Quando si eseguono calcoli utilizzando i valori misurati, ricordarsi di non eseguire calcoli con una risoluzione superiore a quella della misurazione originale. Tali cifre aggiuntive non sono significative e non devono essere incluse. Ad esempio, quando si calcola l'area del quadrato con una lunghezza del lato di 1,15, vediamo che la lunghezza ha tre cifre significative. Quindi, la risposta dovrebbe avere anche tre cifre significative.
L'area calcolata di 1,3225 pollici al quadrato ha cinque cifre e introduce nel calcolo una certezza che non c'era nella misurazione originale. Pertanto, l'area corretta è di 1,32 pollici quadrati.
In questo laboratorio, eserciterai le corrette abilità di laboratorio misurando la densità di un uovo e utilizzando cifre significative nei tuoi calcoli e registrazioni. Inoltre, ti eserciterai a tenere registri nel tuo quaderno di laboratorio ed esaminerai l'accuratezza delle misurazioni con la vetreria volumetrica.

tecniche di laboratorio

<h4>Precisione di misurazione</h4>
La capacità di ripetere un esperimento e ottenere gli stessi risultati, o riproducibilità, è essenziale nella ricerca scientifica. Tuttavia, è impossibile ripetere un esperimento se non si sa come è stato fatto. Pertanto, gli scienziati tengono registrazioni dettagliate dei loro esperimenti in quaderni di laboratorio. Questi registri includono informazioni importanti come la quantità di ciascun materiale utilizzato e le descrizioni di ogni fase della procedura.
Le apparecchiature, come bilance e vetreria volumetrica o graduata, vengono utilizzate per misurare composti solidi e liquidi per gli esperimenti. La precisione di ogni misurazione è limitata dall'attrezzatura utilizzata. Le bilance e gli altri strumenti con lettura digitale visualizzano automaticamente i valori con la massima precisione che possono supportare. La precisione della vetreria graduata e dei righelli dipende dall'incremento, che è la quantità rappresentata dalla distanza più piccola tra due segni.
La superficie della maggior parte dei liquidi si curva verso l'alto ai bordi in contenitori di vetro. Questo tipo di superficie liquida curva è chiamata menisco concavo. Quando i bordi del liquido si curvano verso il basso, si parla di menisco convesso. Quando si misurano i volumi di liquido, il punto di riferimento per la parte superiore del liquido è la parte inferiore di un menisco concavo o la parte superiore di un menisco convesso. Per identificare con precisione la posizione del menisco, i volumi del liquido vengono letti osservando la superficie del liquido dal lato all'altezza degli occhi. Guardando il liquido dall'alto o dal basso, il livello della superficie del liquido apparirà più alto o più basso di quanto non sia in realtà.
Quando il punto di riferimento del menisco tocca un segno su vetreria graduata o volumetrica, la vetreria mantiene il volume definito per quel segno. La vetreria volumetrica è progettata per misurare un volume specifico, quindi ha un solo segno. La vetreria graduata è progettata per misurare una gamma di volumi, quindi ha molti segni, o graduazioni, che vengono etichettati a intervalli regolari. Sia la vetreria graduata che quella volumetrica possono avere ulteriori informazioni fornite dal produttore sulla loro precisione.
<h4>Taratura e incertezza</h4>
I produttori calibrano le apparecchiature per garantire che le misurazioni siano accurate entro un intervallo di incertezza specificato. Ad esempio, una bilancia analitica ad alta precisione può leggere con quattro cifre decimali (0,0000 g) con un'incertezza di ± 0,0001 g. Una lettura di 0,0345 g indica che il valore reale è compreso tra 0,0344 g e 0,0346 g.
La vetreria in genere ha la sua incertezza di misura stampata su di essa. Per registrare con precisione le misurazioni del volume, è necessario considerare sia l'incremento che l'incertezza. Ad esempio, una misurazione precisa del volume in un cilindro graduato da 100 mL con incrementi di 1 mL e un'incertezza di ± 0,5 mL verrebbe registrata al decimo posto (000,0 mL ± 0,5 mL). Se il punto di riferimento del menisco cade tra due segni, è necessario stimare un valore per la decima posizione; In caso contrario, lasciarlo su 0. Poiché la temperatura influisce sul volume, su di essa verrà stampata la temperatura per la quale la vetreria è calibrata.
La vetreria è calibrata per contenere (TC) o per erogare (TD). La vetreria TC trattiene il volume specificato di liquido quando viene riempita fino al segno, ma una piccola quantità di liquido rimarrà quando viene versata in un altro contenitore. Le soluzioni vengono spesso preparate nella vetreria TC perché l'accuratezza del volume della soluzione influisce sull'accuratezza della concentrazione. I matracci volumetrici sono tipicamente calibrati per contenere.
La vetreria TD contiene un po' più della quantità di liquido specificata quando viene riempita fino al segno, ma eroga solo il volume specificato. Pertanto, la vetreria TD non deve essere svuotata completamente durante l'erogazione di liquidi. Questo tipo di vetreria è utile per trasferire un volume preciso di liquido in un altro contenitore. Sia le pipette graduate che quelle volumetriche sono generalmente calibrate per erogare.
Se non diversamente specificato, si presume che l'incertezza di un numero sia sulla scala dell'ultima cifra. Pertanto, è particolarmente importante segnalare l'incertezza di una misurazione se l'incertezza è su scala più ampia. Per i righelli e la vetreria graduata senza un'incertezza nota, l'incertezza è stimata come la metà dell'incremento più piccolo. La cifra incerta si basa su dove si trova il menisco tra due segni di spunta.
<h4>Cifre significative</h4>
Le cifre significative sono i numeri di un valore che sono significativi o essenziali per esprimere tale valore con la precisione appropriata. Tutti i numeri diversi dagli zeri iniziali (0,001), dagli zeri finali (1.000) o dai moltiplicatori di notazione scientifica (10x) sono sempre significativi.
Gli zeri iniziali non sono mai significativi perché possono essere rimossi riscrivendo il numero in notazione scientifica o, se si tratta di un'unità SI, in unità più piccole. Ad esempio, ci sono solo tre cifre significative nel valore 0,00123 m perché può essere riscritto come 1,23 × 10-3 m o 1,23 mm senza perdere alcuna informazione. Si noti che il fattore di scala tra diversi multipli della stessa unità SI non influisce sul numero di cifre significative.
Gli zeri finali sono significativi quando si trovano prima o dopo una virgola. Ad esempio, la misura 100,110 mL ha sei cifre significative e 100,0 mL ne ha quattro. Si presume che gli zeri finali in un numero scritto senza virgola decimale siano insignificanti, a meno che non siano contrassegnati diversamente. Ci sono diverse convenzioni per contrassegnare zeri significativi in questi casi, ma per evitare ambiguità è consigliabile riscrivere quei valori in notazione scientifica. Se la misura è in unità SI, utilizzare unità più grandi.
La precisione di una misurazione limita la precisione di qualsiasi valore calcolato da essa. Un valore calcolato ha lo stesso numero di cifre significative della misura o del valore meno preciso utilizzato nel suo calcolo. Se il risultato ha troppe cifre significative, viene arrotondato alla precisione appropriata. Se il risultato ha un numero insufficiente di cifre significative, viene esteso con zeri finali significativi per preservare la precisione. Le cifre significative dei valori derivati sperimentalmente, come la massa molare, la densità o alcuni fattori di conversione unitaria, devono essere prese in considerazione quando vengono utilizzate nei calcoli.
Il numero di cifre significative in un valore calcolato non è limitato da costanti fisiche o matematiche in formule o numeri esatti, come il numero di punti dati acquisiti in un esperimento. Ad esempio, la formula per calcolare il volume di una sfera è V = 4/3πr3. Il numero di cifre significative nel volume calcolato è influenzato solo dal numero di cifre significative nella misura del raggio r. 4/3 e π sono costanti e 3 è semplicemente la notazione per un'operazione matematica.
Anche i fattori di conversione definiti vengono considerati come costanti. Ad esempio, il pollice è definito esattamente come 25,4 millimetri; Pertanto, il numero di cifre significative del valore convertito dipende solo dalla misurazione originale. Controlla sempre se il fattore di conversione è esattamente definito o un valore sperimentale durante la conversione tra unità.
Per semplici addizioni e sottrazioni di misurazioni, utilizziamo l'aritmetica della significatività per determinare il numero di cifre significative. In questo caso, la risposta ha tante cifre decimali quanto la misura con il minor numero di cifre decimali, indipendentemente dal numero di cifre significative. Quindi, 15.643,7 ml + 0,613 ml = 15.644,3 ml.
Per calcoli a più fasi o equazioni complesse che si suddividono in parti più piccole per risolvere, è necessario mantenere almeno una o due cifre insignificanti sui valori intermedi. Ad esempio, se si calcolano separatamente i valori del numeratore e del denominatore di una frazione prima di dividerli, è necessario mantenere le cifre insignificanti del numeratore e del denominatore quando li si divide. In questo modo si riduce al minimo l'errore di arrotondamento, che è la differenza rispetto al numero che si otterrebbe se si inserisse l'intera formula nella calcolatrice in una sola volta. Se annoti questi valori intermedi, dovresti notare quali cifre sono insignificanti.
<h4>Referenze</h4>
Harris, DC (2015). Analisi chimica quantitativa. New York, NY: W.H. Freeman e compagnia.

Tecniche di laboratorio

Precisione di misurazione
La capacità di ripetere un esperimento e ottenere gli stessi risultati, o riproducibilità, è essenziale nella ricerca scientifica. Tuttavia...

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JoVE Lab Manual

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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...

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Oxidation States in Redox Reactions

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Gas Laws Behind the Ideal Gas Equation

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Acids, Bases, and pH in Titration

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Buffer pH and the Common Ion Effect

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Solubility in Water and Other Solvents

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Hydrogen Emission Lines

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Absorbance Spectra and Beer-Lambert Analysis

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Reaction Order and Rate Constants

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Reaction Rate, Arrhenius, and Catalysts

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Electroplating with Electrolytic Cells

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Recording a Reproducible Lab Experiment

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Organic Lab Glassware and Safe Handling

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How Impurities Change Melting Points

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Boiling Point and Vapor Pressure

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Purifying Crystals by Solubility

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Separating Mixtures with Solvent Extraction

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simple distillation

Separating Liquids by Boiling Point

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Steam Distillation and Low-Boiling Separation

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TLC Separation by Polarity

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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...

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Luminol Chemiluminescence in Forensics

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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

Video completi e incentrati sul curriculum sia per gli istruttori che per gli studenti nei corsi di laboratorio di Chimica introduttiva.

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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

Preparati a insegnare Tecniche di laboratorio con questa guida per istruttori di 1 minuti. Copre i passaggi chiave di preparazione per il laboratorio Chemistry su JoVE Lab Manual.

Preparazione dell'istruttore per Tecniche di laboratorio in Chemistry - Oltre 9.8K visualizzazioni | JoVE Lab Manual

Segui le procedure passo dopo passo di Tecniche di laboratorio in questo video di protocollo studente di 9 minuti. Parte della collezione Chemistry su JoVE Lab Manual.

Protocollo studente per Tecniche di laboratorio in Chemistry - Oltre 30K visualizzazioni | 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

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