Laboratory Weighing Techniques Quiz
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Questions and Answers

What advantage do stirred water baths have over non-circulating water baths?

  • Lower cost
  • Quicker heat-up time
  • Lighter weight
  • More accurate temperature control (correct)

    • Which type of water bath relies primarily on convection?

  • Cooled water bath
  • Stirred water bath
  • Non-circulating water bath (correct)
  • Circulating water bath

    • For applications requiring precise temperature uniformity, which water bath is most suitable?

  • Non-circulating water bath
  • Circulating water bath (correct)
  • Boiling water bath
  • Shaking water bath

    • What is a typical feature of boiling water baths?

    <p>Analog control for temperature regulation</p> Signup and view all the answers

    What function does an immersion thermostat serve in cooled water baths?

    <p>It maintains temperatures below ambient conditions</p> Signup and view all the answers

    What is one primary feature of the balances described?

    <p>Internal calibration option</p> Signup and view all the answers

    Which of the following features is common in shaking water baths?

    <p>Speed-controlled shaking platform</p> Signup and view all the answers

    What effect does weighing a hot item have on the scale reading?

    <p>It displays a lower weight due to buoyancy.</p> Signup and view all the answers

    Why is it important to keep the balance clean?

    <p>Cleaning the balance reduces the risk of chemical reactions.</p> Signup and view all the answers

    What is a key consideration when using laboratory water baths below 4°C?

    <p>Filling with a liquid that does not freeze</p> Signup and view all the answers

    What is typically included in the design of boiling water baths?

    <p>Water level device</p> Signup and view all the answers

    What is the lowest class of weight set that provides average precision?

    <p>Class M</p> Signup and view all the answers

    What should users do before using items on the balance?

    <p>Ensure items are at room temperature.</p> Signup and view all the answers

    Which of the following is NOT a standard feature of the balances mentioned?

    <p>Automatic data logging</p> Signup and view all the answers

    What can be used to clean dust off the balance?

    <p>A camel's hair brush</p> Signup and view all the answers

    What is a likely consequence of not regularly calibrating a balance?

    <p>It may yield inaccurate weight measurements.</p> Signup and view all the answers

    What is the primary function of an analytical balance?

    <p>To measure the mass of objects</p> Signup and view all the answers

    Why must analytical balances be covered by a draft shield?

    <p>To eliminate the effect of air currents on measurements</p> Signup and view all the answers

    Which component of an analytical balance allows for precise leveling?

    <p>Leveling feet</p> Signup and view all the answers

    What accuracy can actual analytical balances achieve at full capacity?

    <p>One part in 106</p> Signup and view all the answers

    How does an equal arm balance determine the mass of an object?

    <p>By summing the weights on both sides until balanced</p> Signup and view all the answers

    What is a characteristic feature of modern analytical balances?

    <p>Automatic internal calibration mechanisms</p> Signup and view all the answers

    What is the main purpose of laboratory water baths?

    <p>To cool water or remove heat from equipment</p> Signup and view all the answers

    What is the role of a beam arrest in an analytical balance?

    <p>To prevent damage during weighing</p> Signup and view all the answers

    Which material is commonly used for the interiors of laboratory water baths?

    <p>Stainless steel</p> Signup and view all the answers

    What is the maximum weighing capacity typical for an analytical balance?

    <p>From 1 g to a few kilograms</p> Signup and view all the answers

    Which practice is NOT recommended when using water baths?

    <p>Heating bath fluid above its flash point</p> Signup and view all the answers

    What is the recommended action to prevent organism growth in water baths?

    <p>Raise the temperature to 90 °C weekly</p> Signup and view all the answers

    What should be done if liquid that gives off fumes is used in a water bath?

    <p>Operate the bath in a fume hood</p> Signup and view all the answers

    Which aspect of the internal tank dimensions is misleading?

    <p>The total volume capacity listed</p> Signup and view all the answers

    For anaerobic cultivation, which gas mixture is replaced in the jar?

    <p>10% CO2 + 90% H2</p> Signup and view all the answers

    What signifies a successful anaerobiosis in the use of anaerobic jars?

    <p>A growth free culture plate</p> Signup and view all the answers

    What is one of the main uses of colorimeters in chemistry laboratories?

    <p>Determining the concentrations of plant nutrients</p> Signup and view all the answers

    How does a colorimeter determine the concentration of an unknown sample?

    <p>It compares the sample to a calibration curve created from known concentrations</p> Signup and view all the answers

    What role does the Greek letter lambda (λ) play in colorimetry?

    <p>It denotes the specific wavelength affected by a reaction</p> Signup and view all the answers

    What is a common application of colorimeters beyond laboratory research?

    <p>Testing water quality for specific chemicals</p> Signup and view all the answers

    Which of the following is NOT a factor that influences the results obtained from a colorimeter?

    <p>The temperature of the surrounding environment</p> Signup and view all the answers

    What is the observable change noted in colorimetry during a reaction?

    <p>Color change of a solution</p> Signup and view all the answers

    For what purpose can a colorimeter be used in food quality assessment?

    <p>To monitor the color in vegetable products and sugar</p> Signup and view all the answers

    What process do colorimeters utilize to assess the concentration of a solution?

    <p>Measurement of light absorption as it passes through</p> Signup and view all the answers

    Study Notes

    Analytical Balance

    • Used for precise weighing in laboratories
    • Measures mass, not weight, unaffected by gravity
    • Capacity ranges from 1 gram to a few kilograms
    • Precision and accuracy often exceed one part in 10⁶
    • Features: beam arrest, pan for weighing objects, leveling feet
    • Sensitive to air currents, requires draft shield for protection

    Equal Arm Balance/Trip Balance

    • Modern version of ancient Egyptian scales
    • Two pans on opposite sides of a lever
    • Used to determine mass by balancing weights
    • Can also be used to compare the masses of two objects
    • Commonly used in laboratories for tasks like determining liquid density

    Balance and Scale Care and Use

    • Items to be measured should be at room temperature
    • Keep scales clean to avoid corrosion and contamination
    • Camel's hair brush recommended for dust removal
    • Regular calibration is essential for accuracy
    • Weight sets are available for self-calibration or use professionals

    Circulating Water Baths

    • Ideal for temperature uniformity and consistency
    • Water is circulated throughout the bath for consistent temperature

    Non-Circulating Water Baths

    • Rely on convection for heat transfer, less accurate for temperature control
    • Stirring can be added to improve heat transfer

    Shaking Water Baths

    • Have a shaking platform tray (usually reciprocal motion)
    • Hold different vessels using adaptors

    Laboratory Water Bath Accessories

    • Lift-off or hinged lids, stainless steel or plastic
    • Racks for holding tubes and flasks
    • Holes with concentric rings in lids for flasks of various sizes

    Care and Maintenance of Water Baths

    • Do not use for moisture-sensitive or pyrophoric reactions
    • Do not heat bath fluid above its flash point
    • Regular monitoring of water level and use distilled water only
    • Add disinfectants to prevent growth of organisms
    • Raise temperature to 90 °C or higher weekly for decontamination
    • Water-resistant markers are recommended
    • Operate in a fume hood or well-ventilated area
    • Keep cover closed to prevent evaporation and aid in reaching high temperatures

    Anaerobic Jars

    • Used to create an oxygen-free environment for culturing anaerobic bacteria
    • Culture media and indicator system (e.g., Pseudomonas aeruginosa) are placed inside the jar
    • Air is pumped out and replaced with hydrogen or a hydrogen/carbon dioxide mixture

    Colorimeters

    • Measure light absorbance through solutions
    • Used for assessing color in various applications
    • Used to determine the concentration of chemicals or materials in a solution
    • Can be used for water quality testing, food and beverage analysis, and biological research
    • Several known samples of the solution are tested to create a calibration curve
    • Unknown samples are then compared to the curve to determine concentration

    How to Use a Colorimeter

    • Different types of colorimeters exist, but the procedures are similar
    • Change in color is observed as a reaction takes place
    • The wavelength of light most affected by the reaction is denoted by λmax
    • Wavelength selection can be done using different methods

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    Laboratory Instrumentation and Techniques PDF

    Description

    Test your knowledge on laboratory weighing techniques, including the use of analytical and equal arm balances. This quiz covers the care and usage of balances and scales, ensuring accuracy and precision in measurements. Ideal for students and professionals in scientific fields.

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