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

Medições precisas de volume são cruciais para análises baseadas em soluções. O equipamento volumétrico padrão inclui frascos, pipetas e buretas.
Os frascos volumétricos são usados para preparar e diluir soluções para um volume específico. Eles são marcados como TC, que significa "conter".
Eles são calibrados para conter um volume preciso em temperaturas especificadas, onde o coeficiente mínimo de expansão do vidro permite um volume quase constante, apesar de pequenas alterações.
As pipetas rotuladas como TD fornecem um volume específico a uma determinada temperatura. Eles são calibrados para levar em conta a drenagem do filme nas paredes de vidro, que varia de acordo com o tempo de entrega.
As pipetas volumétricas com calibração adequada fornecem um único volume com precisão de até quatro ou cinco algarismos significativos. As pipetas de medição fornecem diferentes volumes com menor precisão de até três algarismos significativos.
Uma bureta é um tubo calibrado para segurar o titulante que pode ser dispensado com precisão através do sistema de válvula manual para controlar o fluxo do titulante.

calibração de vidraria

A calibração precisa de vidraria, como frascos volumétricos, pipetas e buretas, é essencial para garantir medições precisas no laboratório analítico. A calibração ajuda a manter a consistência entre as medições e evita erros decorrentes de volumes imprecisos.

Volumetric flasks

Os frascos volumétricos são projetados para preparar soluções aquosas com volumes precisos, com uma linha de calibração no gargalo. Para calibrar um frasco volumétrico, é importante enchê-lo com água destilada até que o menisco (a superfície curva do líquido) se alinhe com a marca de calibração. Visualizar o menisco no nível dos olhos garante leituras precisas. A calibração é normalmente realizada em uma temperatura específica (~20°C) para levar em conta o efeito da temperatura no volume. Se o nível da água estiver acima da linha, drene-a cuidadosamente até atingir a marca; se a linha de água estiver abaixo, adicione mais água gota a gota até atingir a marca. Após a calibração, a capacidade do frasco pode ser confirmada pesando a água e comparando-a com o valor teórico com base em sua densidade.

Pipetas

As pipetas são usadas para transferir volumes específicos de líquido.

Pipetas Volumétricas: são projetadas para fornecer um volume único e altamente preciso, normalmente com quatro ou cinco algarismos significativos. Para calibração, a pipeta é primeiro limpa e enxaguada com a solução a ser medida, preenchida até a marca de calibração e drenada completamente para um recipiente. A precisão é então verificada pesando a água fornecida e comparando-a com o volume teórico com base na densidade da água.

Pipetas Graduadas: diferentemente das pipetas volumétricas, as pipetas graduadas são marcadas com uma série de linhas e podem fornecer vários volumes, mas com precisão ligeiramente menor — geralmente até três algarismos significativos. O menisco também deve ser cuidadosamente observado durante a calibração e medição.

Bureta

Uma bureta é um tubo de vidro longo e graduado, com uma torneira em uma extremidade que dispensa com precisão quantidades variáveis ​​de uma solução, particularmente em titulações. Ao calibrar uma bureta, certifique-se de que o menisco esteja corretamente alinhado com as marcações antes e depois da titulação e verifique se o volume dispensado é o esperado comparando o peso da água fornecida com seu valor teórico. O reservatório da bureta contém marcações para indicar o volume do líquido. A torneira na parte inferior serve como uma válvula manual que permite aos usuários controlar o fluxo de líquido do reservatório, permitindo uma medição precisa da quantidade dispensada.

Outros Vidrarias

Outros tipos de vidrarias de laboratório, como cilindros graduados, também são comumente usados ​​para medições de volume, mas oferecem menor precisão do que equipamentos volumétricos. Eles normalmente fornecem volumes com até três algarismos significativos, adequados para trabalhos menos precisos. No entanto, a calibração desses itens ainda é importante para manter a confiabilidade da medição.

A calibração da vidraria do laboratório garante medições precisas e confiáveis, o que é crucial para manter a integridade dos resultados analíticos. Seja usando frascos volumétricos, pipetas, buretas ou outras vidrarias, as técnicas de calibração adequadas ajudam a evitar erros e melhorar a precisão do trabalho de laboratório.

Calibração de Vidraria

A calibração precisa de vidraria, como frascos volumétricos, pipetas e buretas, é essencial para garantir medições precisas no ...

Education

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidade 1

Method Development and Sampling Techniques

Desenvolvimento de Métodos e Técnicas de Amostragem

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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

development of analytical methods

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How Analytical Methods Are Checked

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Measuring Analyte Concentration

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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

Standard solutions are prepared to have a precisely known concentration or composition. In analytical chemistry, this accuracy is important because it supports reliable results. A primary standard is a highly pure, stable substance with a high molar mass. It is fully soluble in water, which is the most commonly used solvent in analytical chemistry. A primary standard solution can be used to standardize a secondary standard. Secondary standards have known concentrations, but they are usually...

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Blank Solutions in Analytical Testing

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sample preparation for analysis: overview

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sample-preparation-for-analysis-advanced-techniques

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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

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Calibrating Lab Glassware for Accurate Volume

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