Lab #10: The Effect of Mass on Energy



Accuracy and Precision When Determining the Density of Water

Objective(s) - to evaluate the precision and accuracy of different laboratory glassware when determining the density of water.

Hypotheses: Four different pieces of glassware will be tested today – 50 mL graduated cylinder, 100 mL graduated cylinder, 50 mL beaker, and 100 mL beaker.

Which piece of glassware should result in the most precise measurements for the density of water and why?

Which piece of glassware should result the most accurate measurement for the density of water and why?

Materials and Methods

Part I –Beaker Measurements

1 – Obtain about 450 mL of water in a beaker to use at your station. (Pick a good size for this!)

2 – Get the mass of a clean, dry, 50 mL beaker using an electronic balance. Record this value in table 1.

3 - Fill the 50 mL beaker up to 35 mL with water, using no other glassware. Record this volume in table 1.

4 – Get the mass of this beaker plus water and record in table 1.

5 – Empty out the beaker, dry it well, and repeat all steps above two more times.

6 – Get the mass of a clean, dry 100 mL beaker using an electronic balance. Record this value in table 2.

7 - Fill the 100 mL beaker up to 35 mL with water, using no other glassware. Record this volume in table 2.

8 – Get the mass of this beaker plus water and record in table 2.

9 – Empty out the beaker, dry it well, and repeat all steps above two more times.

Part II – Graduated Cylinder Measurements

1 – Refill your beaker with 450 mL of water to use at your station.

2 – Get the mass of a clean, dry (but don’t stick paper towels in it!), 50 mL graduated cylinder using an electronic balance. Record this value in table 3.

3 - Fill the 50mL graduated cylinder up to 35.0 mL with water, using no other glassware. Record this volume in table 3 to the nearest mL.

4 – Get the mass of this graduated cylinder plus water and record in table 3.

5 – Empty out the graduated cylinder, dry it as much as possible (again don’t shove paper towel in it), and repeat all steps above two more times.

6 – Get the mass of a clean, dry, 100 mL graduated cylinder using an electronic balance. Record this value in table 4.

7 - Fill the 100 mL graduated cylinder up to 35.0 mL with water, using no other glassware. Record this volume in table 4 to the nearest mL.

8 – Get the mass of this graduated cylinder plus water and record in table 4.

9 – Empty out the graduated cylinder, dry it (without getting paper towel stuck), and repeat all steps above two more times.

Results

Record results in tables below. Be sure to include units! There is some math needed to get the mass of water alone.

Table 1 – 50 mL Beaker Measurements

| |Trial #1 |Trial #2 |Trial #3 |Average |

|Mass of Empty Beaker | | | |X |

|Mass of Beaker Plus Water | | | |X |

|Mass of Water | | | | |

|Volume of Water | | | | |

Table 2 – 100 mL Beaker Measurements

| |Trial #1 |Trial #2 |Trial #3 |Average |

|Mass of Empty Beaker | | | |X |

|Mass of Beaker Plus Water | | | |X |

|Mass of Water | | | | |

|Volume of Water | | | | |

Table 3 – 50 mL Graduated Cylinder Measurements

| |Trial #1 |Trial #2 |Trial #3 |Average |

|Mass of Empty Graduated | | | |X |

|Cylinder | | | | |

|Mass of Graduated Cylinder | | | |X |

|Plus Water | | | | |

|Mass of Water | | | | |

|Volume of Water | | | | |

Table 4 – 100 mL Graduated Cylinder Measurements

| |Trial #1 |Trial #2 |Trial #3 |Average |

|Mass of Empty Graduated | | | |X |

|Cylinder | | | | |

|Mass of Graduated Cylinder | | | |X |

|Plus Water | | | | |

|Mass of Water | | | | |

|Volume of Water | | | | |

Calculate the average density for each piece of glassware. D=m/V Then calculate the percent error given the accepted value of water density is 1.00 g/mL.

Percent error = accepted value – experimental value x 100

accepted value

Fill out this summary table #5.

Table #5 – Density and Percent Error

|Type of Glassware |Average Density |Percent Error |

| | | |

| | | |

| | | |

| | | |

Analyze tables 1 – 4 to determine qualitatively which piece of glassware seems to take the most precise results. We could have calculated standard deviation for this but are going to make it simple and just analyze by looking and estimating which piece of glassware produced the most consistent data when measuring mass of a given volume.

Lab Report – Specifics and Hints for this Lab!

Introduction background topics should include at least: density definition, very brief history of density including Archimedes, density as a physical property of matter, accuracy vs. precision, beakers and graduated cylinders and their uses in labs. Reliable sources must be used – not just class notes. Don’t go overboard nor should you skimp. Find a happy medium. Be sure to read original guidelines about how to construct this section and what else to include besides background. Be sure you have many in text citations!

Materials and Methods section should include everything done but in past tense, paragraph form instead of steps as listed above. Recall that materials are NOT listed separately. Only include parts of procedure, not clean up and NOT later analysis or little notes from me in parentheses. You can use a lot of the same language as I did in the original procedure without it being plagiarism but it does need to be in past tense, read in paragraphs instead of steps, and it can’t use any personal pronouns! Passive voice passive voice passive voice!!

Include all five tables above in results section. Be sure to construct them carefully and include units and measurements to proper decimal places.

DO NOT show the simple subtraction used to get masses of water alone.

DO show all calculations for density (4 of them) using the 3 step method discussed in lab/class.

DO show all calculations for percent error (4 of them) using the 3 step method discussed in lab/class.

Calculations are a subsection underlined and either typed or handwritten – see original guidelines for more info.

Table 5 can appear either before Calculations or after – your choice since it is summative. All tables are results and calculations are also part of results.

*** Construct a bar graph showing glassware type on x axis and density on y axis. Also include a fifth bar for accepted value of water density of 1.00 g/mL. This must be a hand drawn graph, which will be Figure #1 unless you included figures in your introduction. See original guidelines for more info.

The Discussion section must infer which piece of glassware was most precise in use by looking at precision of water masses obtained throughout trials. It must also infer which piece of glassware was most accurate, using data/results for density to back it up. At this point the hypotheses can be discussed.

The Discussion should explain WHY results were obtained and pull in some of the intro theory and definitions as needed to help explain what was going on in the lab.

Discuss ALL error sources with specifics!! And HOW the error source affected results.

See original guidelines for more info.

Don’t forget References section and use my quick reference APA guide and/or the link on our class website.

Everyone should have an appended bar graph and possibly appended calculations if attached at end.

Use the original guidelines!! Use the hints and reminders to do a check of your report before handing it in!

Turn it in using by class time on the day the report is due. A hard copy is also due at the beginning of class. Late 1 minute to late 1 day = - 15 points. Any day after that lab reports are accepted but can receive a maximum of 50% credit. Last day accepted is 1 week before end of quarter, date TBA.

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