Name: calibrating lab glassware for accurate volume
Uploaded: 2024-12-05T18:31:54.000Z
Duration: 1 min 11 s
Channel: JoVE

Des mesures de volume précises sont cruciales pour les analyses basées sur des solutions. L’équipement volumétrique standard comprend des flacons, des pipettes et des burettes.
Les fioles jaugées sont utilisées pour préparer et diluer des solutions pour un volume spécifique. Ils sont marqués TC, qui signifie « contenir ».
Ils sont calibrés pour contenir un volume précis à des températures spécifiées, où le coefficient minimum de dilatation du verre permet un volume presque constant malgré des modifications mineures.
Les pipettes étiquetées TD délivrent un volume spécifique à une température donnée. Ils sont calibrés pour tenir compte du drainage du film sur les parois en verre, qui varie avec le délai de livraison.
Les pipettes jaugées avec un calibrage approprié délivrent un seul volume avec une précision allant jusqu’à quatre ou cinq chiffres significatifs. Les pipettes de mesure délivrent différents volumes avec une précision inférieure allant jusqu’à trois chiffres significatifs.
Une burette est un tube calibré pour maintenir le titrant qui peut être distribué avec précision via le système de valve manuelle pour contrôler le débit du titrant.

Étalonnage de la verrerie

L'étalonnage précis de la verrerie, comme les fioles jaugées, les pipettes et les burettes, est essentiel pour garantir des mesures précises dans le laboratoire d'analyse. L'étalonnage permet de maintenir la cohérence entre les mesures et d'éviter les erreurs résultant de volumes inexacts. Fioles jaugées

Les fioles jaugées sont conçues pour préparer des solutions aqueuses de volumes précis avec précision grâce à une ligne d'étalonnage sur le col. Pour étalonner une fiole jaugée, il est important de la remplir d'eau distillée jusqu'à ce que le ménisque (la surface incurvée du liquide) s'aligne avec le repère d'étalonnage. La visualisation du ménisque au niveau des yeux garantit des lectures précises. L'étalonnage est généralement effectué à une température spécifique (~ 20 °C) pour tenir compte de l'effet de la température sur le volume. Si le niveau d'eau est au-dessus de la ligne, égouttez-la soigneusement jusqu'à ce qu'elle atteigne le repère; si la ligne d'eau est en dessous, ajoutez plus d'eau goutte à goutte jusqu'à ce qu'elle atteigne le repère. Après l'étalonnage, la capacité du flacon peut être confirmée en pesant l'eau et en la comparant à la valeur théorique basée sur sa densité.

Pipettes

Les pipettes sont utilisées pour transférer des volumes spécifiques de liquide.

Pipettes volumétriques: elles sont conçues pour délivrer un volume unique et très précis, généralement à quatre ou cinq chiffres significatifs. Pour l'étalonnage, la pipette est d'abord nettoyée et rincée avec la solution à mesurer, remplie jusqu'au repère d'étalonnage et laissée s'écouler complètement dans un récipient. La précision est ensuite vérifiée en pesant l'eau délivrée et en la comparant au volume théorique basé sur la densité de l'eau.

Pipettes graduées: contrairement aux pipettes volumétriques, les pipettes graduées sont marquées d'une série de lignes et peuvent délivrer plusieurs volumes mais avec une précision légèrement inférieure, généralement jusqu'à trois chiffres significatifs. Le ménisque doit également être soigneusement observé pendant l'étalonnage et la mesure.

Burette

Une burette est un long tube en verre gradué doté d'un robinet à une extrémité qui distribue avec précision des quantités variables d'une solution, en particulier dans les titrages. Lors de l'étalonnage d'une burette, assurez-vous que le ménisque est correctement aligné avec les repères avant et après le titrage, et vérifiez que le volume distribué est conforme aux attentes en comparant le poids de l'eau délivrée à sa valeur théorique. Le réservoir de la burette contient des repères pour indiquer le volume du liquide. Le robinet d'arrêt ou le robinet situé au fond sert de vanne manuelle qui permet aux utilisateurs de contrôler le débit de liquide du réservoir, ce qui permet une mesure précise de la quantité distribuée.

Autres verreries

D'autres types de verrerie de laboratoire, comme les cylindres gradués, sont également couramment utilisés pour les mesures de volume, mais offrent une précision inférieure à celle des équipements volumétriques. Ils fournissent généralement des volumes allant jusqu'à trois chiffres significatifs, adaptés à un travail moins précis. Cependant, l'étalonnage de ces éléments reste important pour maintenir la fiabilité des mesures.

L'étalonnage de la verrerie de laboratoire garantit des mesures précises et fiables, ce qui est essentiel pour maintenir l'intégrité des résultats analytiques. Qu'il s'agisse de fioles jaugées, de pipettes, de burettes ou d'autres verreries, des techniques d'étalonnage appropriées aident à prévenir les erreurs et à améliorer la précision du travail en laboratoire.

Un étalonnage précis de la verrerie, telle que les fioles jaugées, les pipettes et les burettes, est essentiel pour garantir des mesures précises dans le ...

Education

Enseignement

JoVE Core

Analytical Chemistry

Chimie analytique

Unit 1

Unité 1

Method Development and Sampling Techniques

Développement de méthodes et techniques d'échantillonnage

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Glassware Calibration

calibrating lab glassware for accurate volume

Calibrating lab glassware helps students measure liquids accurately in the analytical laboratory. It reduces volume errors and supports consistent results across measurements. This matters when using volumetric flasks, pipettes, burettes, and other tools that depend on precise volume readings.

Volumetric flasks are used to prepare aqueous solutions with a precise final volume. They have a calibration line on the neck. To calibrate one, fill it with distilled water until the meniscus, the curved surface of the liquid, lines up with the mark at eye level. This is usually done at about 20°C because temperature can affect volume. If the water rises above the line, drain it carefully. If it is below the line, add water drop by drop until it reaches the mark. The flask’s capacity can then be checked by weighing the water and comparing it with the theoretical value from its density.

Pipettes are used to transfer set amounts of liquid. Volumetric pipettes are made to deliver one highly accurate volume, often to four or five significant figures. To calibrate one, clean it and rinse it with the solution to be measured, fill it to the calibration mark, and let it drain completely into a container. The volume delivered is checked by weighing the water and comparing it with the theoretical volume based on water density. Graduated pipettes have a series of marks and can deliver different volumes, but they are slightly less accurate. They are generally used to about three significant figures, so the meniscus must still be read carefully.

Burettes are long, graduated glass tubes with a tap at one end. They are used to dispense variable amounts of solution, especially during titrations. When a burette is calibrated, the meniscus must be aligned with the markings before and after use. The volume dispensed is then compared with the expected value by weighing the water delivered. The reservoir shows the liquid level, and the stopcock, or tap, acts as a manual valve that controls flow for precise measurement.

Other glassware, such as graduated cylinders, is also used for measuring volume. These tools are less accurate than volumetric equipment, but they are still useful for work that does not need the highest precision. They usually measure up to three significant figures. Even so, calibration remains important for reliable measurements in the lab. Careful calibration of lab glassware helps protect the accuracy and integrity of analytical results.

Calibrating Lab Glassware for Accurate Volume

calibrating-lab-glassware-for-accurate-volume

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Quality Checks in Analytical Testing

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Calibrating Lab Instruments for Accurate Results

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glassware calibration

Calibrating lab glassware helps students measure liquids accurately in the analytical laboratory. It reduces volume errors and supports consistent results across measurements. This matters when using volumetric flasks, pipettes, burettes, and other tools that depend on precise volume readings. Volumetric flasks are used to prepare aqueous solutions with a precise final volume. They have a calibration line on the neck. To calibrate one, fill it with distilled water until the meniscus, the...

standard solutions

Preparing Standard Solutions in the Lab

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Blank Solutions in Analytical Testing

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sample handling

Sample Transport and Storage Basics

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contaminants and errors

Sampling Errors in Sample Preparation

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key terms and concepts

Learn how volumetric flasks, pipettes, burettes, and graduated cylinders are calibrated to improve volume accuracy, consistency, and lab reliability.

Calibrating Lab Glassware for Accurate Volume | JoVE K12

analytical chemistry

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Calibrating Lab Glassware for Accurate Volume

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