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Chemistry Techniques and Explorations: An Introductory Chemistry Laboratory Manual: 26

Chemistry Techniques and Explorations: An Introductory Chemistry Laboratory Manual
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table of contents
  1. About PA-ADOPT
  2. About OER
  3. About the Author
    1. Author Acknowledgements
    2. Goal of Laboratory Manual
  4. Table of Contents
  5. Safety and Record Keeping
    1. Safety Rules
    2. RAMP Approach to Safety
    3. Laboratory Notebook
    4. References
  6. Separating Substances, Measuring Mass, and Analyzing Data - Technique Laboratory
    1. Introduction for Measurement of Masses
    2. Separating a Heterogeneous Mixture and Determining Masses
    3. Experiment
    4. Safety Considerations
    5. Waste Disposal
    6. Introduction for Treatment of Data
    7. Pre-Lab Questions
    8. Post-Lab Questions
    9. References
  7. Measuring Volumes - Technique Laboratory
    1. Motivation
    2. Cleaning Glassware for Volumetric Measurements
    3. Volume Measuring Devices
    4. Practice Technique for Graduated Cylinder, Volumetric Pipet, and Volumetric Flask
    5. Waste Disposal
    6. Safety Considerations
    7. Pre-Lab Questions
    8. Post-Lab Calculations and Questions
  8. Reaction Types and Qualitative Analysis - Technique Laboratory
    1. Introduction
    2. Observing Chemical Reactions
    3. Oxidation-Reduction Reactions: Movement of electrons
    4. Acid-Base Reactions: Movement of H+
    5. Precipitation Reactions: Solid Formation
    6. Flame Tests
    7. Safety Considerations
    8. Waste Disposal
    9. Pre-lab Questions
    10. Post-Lab Questions
  9. What is Contaminating the Water Supply? - Exploration Laboratory
    1. Background
    2. Experiment
    3. Available Materials
    4. Data Collection
    5. Safety Considerations
    6. Waste Disposal
    7. Pre-Lab Questions
    8. Post-Lab Questions
  10. Titrations Technique Laboratory
    1. Titration Background and Application
    2. Safety Considerations
    3. Disposal of Waste
    4. Laboratory Activities
    5. Calculations
    6. Pre-Lab Questions
    7. Post-Lab Questions
    8. References
  11. What is the Acidity of Vinegar? - Exploration Laboratory
    1. Background
    2. Experiment
    3. Safety Considerations
    4. Disposal of Waste
    5. Pre-Lab Questions
    6. Post-Lab Questions
    7. References
  12. Absorption Spectroscopy Technique Laboratory
    1. Absorbance Spectroscopy Background
    2. Ultraviolet-Visible Absorbance Spectroscopy
    3. Safety Considerations
    4. Disposal of Waste
    5. Laboratory Activities
    6. Calculations
    7. Pre-Lab Questions
    8. Post-Lab Questions
    9. References
  13. What is the Dye Composition of a Drink?-Exploration Laboratory
    1. Background
    2. Experiment
    3. Safety Considerations
    4. Disposal of Waste
    5. Pre-Lab Questions
    6. Post-Lab Questions
    7. References

When you are reading a

graduated cylinder, it is critical

that you take the time to look

closely at the markings and

understand the spacing. Not all

graduated cylinders are the

same, so you can’t assume a

certain marking pattern. In the

picture above each milliliter is

marked (19, 20, 21, and 22).

In addition, there are nine lines

in-between each milliliter value

so each of these lines

represents one-tenth of a

milliliter. When reading the

graduated cylinder in the

picture above, I see the bottom

of the meniscus is in between

the 1st and 2nd line after the 20

mL mark. Notice that the

bottom of the meniscus is

likely to not fall exactly on a

marking, which allows us to

interpolate the value to get the

correct value along with an

estimate of the uncertainty.

My thought process for reading

the cylinder in figure 3.6 is first

to note that the value is

somewhere between 20 and 21 mL, then I go a step further and see it is

between 20.1 and 20.2 mL, and then finally I make my determination of the

recorded value by estimating the last digit. It looks as if it is closer to 20.2 mL

than 20.1 mL, so I would read it as 20.18 mL. Someone else might come along

and have a slightly different estimation of the last digit, maybe they think that it

is 20.16 mL or 20.19 mL. This slight disagreement is fine and gives an

approximation of the uncertainty of the measurement. I would record this value

with four significant digits since my last recorded digit should be the one that has

uncertainty.

26

Close-up of volume measuring device showing markings and meniscus.

Figure 3.6: "Buret" by photobunny is licensed under CC BY-NC-ND 2.0. Figure 3.6: "Buret" by photobunny is licensed under CC BY-NC-ND 2.0.

Figure 3.6: "Buret" by photobunny is licensed under CC BY-NC-

ND 2.0.

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