Measurements and Calculations Laboratory Activity by 6xNrDX

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                 Accuracy, Precision, and Measurements



Introduction

It would be hard to overstate the importance of taking proper
measurements in the chemistry laboratory. The goal of most of the
experiments that you will perform this year is to obtain accurate, precise
data. You will use your data to perform calculations and formulate
conclusions about chemical principles. Obviously, these calculations
and conclusions can only be as accurate as the measurements that they
are based on. For this reason, you must take each measurement to the
maximum accuracy allowed by the instrument you use. The accuracy of
each measurement is limited by two things: the limitations of the
instrument and the care of the experimenter. You must also make sure
that you don’t accidentally claim that a measurement or calculation is
more accurate than it actually is.

Purpose

The objectives of this lab are to:
   Measure each physical quantity to the maximum accuracy allowed
      by the appropriate instrument.
   Record measurements and calculations with the appropriate units
      from the international system of units.
   Calculate volumes and densities to the appropriate number of
      significant digits.

Materials

electronic balance                   100 mL graduated cylinder
50 mL buret                          150 mL beaker
distilled water                      ring stand
buret clamp

Procedure

Measuring Volume Using a Graduated Cylinder
1. Determine the mass of a 100 mL graduated cylinder and record the
   value in Table 1. Remember to include appropriate units and an
   estimation digit for the measurement.
2. Obtain about 100 mL of distilled water in a clean Erlenmeyer flask.
   Determine and record the temperature of the distilled water.

3. Fill the graduated cylinder with distilled water so that the meniscus of
   the water level lines up with the 25 mL calibration mark of the
   cylinder.

4. Dry the outside of the graduated cylinder.

5. Determine the mass of the graduated cylinder and water and record
   the value in Table 1. Remember to include appropriate units and an
   estimation digit for the measurement.

6. Determine the actual amount of water placed in the graduated
   cylinder and record the value in Table 1. Remember to include
   appropriate units and an estimation digit for the measurement.


Measuring Volume with a Beaker
1. Clean and dry a 150 mL beaker.

2. Determine the mass of the beaker and record the value in Table 2.
   Remember to include appropriate units and an estimation digit for the
   measurement.

3. Obtain about 100 mL of distilled water in a clean Erlenmeyer flask.
   Determine and record the temperature of the distilled water.

4. Fill the beaker with distilled water to the 50 mL calibration mark of
   the beaker.

5. Dry the outside of the beaker.

6. Determine the mass of the beaker and water and record the value in
   Table 2. Remember to include appropriate units and an estimation
   digit for the measurement.

7. Record the amount of water placed in the beaker. Remember to
   include appropriate units and an estimation digit for the
   measurement.


Measuring Volume with a Buret

1. Clean and dry a 150 mL beaker.
2. Determine the mass of the beaker and record the value in Table 3.
   Remember to include appropriate units and an estimation digit for the
   measurement.

3. Determine and record the initial liquid level in the buret. Remember
   to include appropriate units and an estimation digit for the
   measurement.

4. Place the 150 mL beaker under the stopcock of the buret.

5. Open the stopcock of the buret and run water into the beaker until
   approximately 25 mL of water has been dispensed.

6. Determine and record the final liquid level in the buret. Remember to
   include appropriate units and an estimation digit for the
   measurement.

7. Determine and record the mass of the beaker and water. Remember
   to include appropriate units and an estimation digit for the
   measurement.

8. Determine and record the temperature of water in the beaker.


Data Analysis

For each problem below, show your work in your laboratory notebook.
Record your answer in the data table. Remember to include appropriate
units and the correct number of significant figures with your answer.


1. Calculate the mass of water in the graduated cylinder. Record your
   answer in Table 1.

2. Using the mass of water and the density of water at the measured
   temperature, calculate the volume of water actually in the graduated
   cylinder. Record this answer in Table 1. Remember,

   Density = mass
             volume


3. Calculate the difference in the observed volume and the calculated
   volume for the graduated cylinder. Record your answer in Table 1.
4. Calculate the mass of water in the 150 mL beaker. Record your
   answer in Table 2.

5. Calculate the actual volume of water in the 150 mL beaker. Record
   your answer in Table 2.

6. Calculate the difference in the observed volume and the calculated
   volume for the graduated cylinder. Record your answer in Table 2.

7. Calculate the mass of water transferred from the buret. Record your
   answer in Table 3.

8. Calculate the volume of water transferred from the buret. Record your
   answer in Table 3.

9. Calculate the actual volume of water transferred from the buret.
   Record your answer in Table 3.

10. Calculate the difference in the observed volume and the calculated
   volume for the buret. Record your answer in Table 3.

Conclusion

1. Based on the data collected in this experiment, which piece of
   volumetric glassware is the most accurate, the graduated cylinder, the
   beaker, or the buret? Use data you collected in this lab to justify
   your answer.

2. Which piece of volumetric glassware allowed you to make the most
   precise measurements? How can you tell?
Table 1. Determining the Accuracy of a Graduated Cylinder

Mass of empty 100 mL graduated
cylinder
Mass of cylinder + water sample

Mass of water in cylinder

Observed volume of water in
cylinder
Temperature of water in cylinder

Density of water at this
temperature
Calculated volume of water
transferred
Difference between observed and
calculated volume




Table 2. Determining the Accuracy of a Beaker

Mass of empty 150 mL beaker

Mass of beaker + water sample

Mass of water in beaker

Observed volume of water in beaker

Temperature of water in beaker

Density of water at this
temperature
Calculated volume of water
transferred
Difference between observed and
calculated volume
Table 3. Determining the Accuracy of a Buret

Mass of empty 150 mL beaker

Initial liquid level in buret

Final liquid level in buret

Volume of liquid transferred

Mass of beaker + water sample

Mass of water in beaker

Temperature of water in beaker

Density of water at this
temperature
Calculated volume of water
transferred
Difference between observed and
calculated volume

								
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