Study of student precision using volumetric glassware

Jason Kenfield
Lafayette High School
Red Lake Falls, Minnesota
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Summary

This lab is designed to have students measure the liquid volume an unknown sample using both a transfer (serological) and volumetric pipette or wheel and pipette bulb, along with an electronic balance. They will then record all of their data onto an excel spreadsheet and do a simple statistical analysis of their data to determine which combination of tools allows for them to measure the volume of a substance with the most precision.

Learning Goals

  • The students will be able to properly use volumetric glassware to measure the volume of any liquid.
  • The students will be able to calculate simple statistics based on their own data.
  • The students will be able to manipulate data on a spreadsheet into a graph that gives a visual aid for a short presentation.

Key Concepts:
  1. Take into account the effect temperature has on the volume of a substance.
  2. The difference between the use of a transfer pipette and a volumetric pipette.

Vocabulary Words:
  1. Percent Error
  2. Pipette
  3. Precision
  4. Histogram

Context for Use

This activity is a lab designed as an introduction to measuring the volume of a liquid using more advanced techniques primarily for 1st year chemistry students at the high school level. You can keep this lab fairly safe just by using deionized water instead of any solutions, or whatever you may wish to use. The lab normally takes three 50 min class periods for data acquisition and one more class period to get the students set up on their spread sheets. I typically use this lab within the first few weeks of the school year to get students acquainted with the use of lab devices and techniques.

Description and Teaching Materials

Materials: (Per group of 2-4)
10 mL Volumetric Pipette
10 mL Serological (transfer) Pipette
Pipette Bulb
Pipettor Wheel
5 50 mL Beakers
Deionized Water at Room Temperature or other solutions
Thermometer
Electronic Balance with precision to 0.01 g

1st Day: Introduce students to the lab by discussing the importance of following directions in order to gain the most precision possible in a laboratory setting. Then introduce the pieces of equipment they are going to use in the lab and tell the students they are to use the pieces however they deem appropriate, while following all safety rules, to get the most precise volume of material. Measure the mass of the water on the electronic scale and have them record all data in table similar to one attached. This data collected is to be labeled the pre-instruction data.

2nd Day: Demonstrate proper use of all the pieces of equipment, remembering that when using a serological (transfer) pipette, always blow the remainder of the solution out of the tip. Where with a volumetric pipette, never blow out the last bit, just touch the tip of the pipette to the side of the container you just transferred to.

3rd Day: Allow students to perform the lab according to the proper techniques that were demonstrated on the prior day, collecting the post-instruction data.

4th Day: Have students create spreadsheets similar to their data tables. Graph % error and also construct a histogram. In the spreadsheets, students are also to determine their own mode, mean, median and standard deviation of their data. The last few parts after they set up their spreadsheets may be assigned as homework. Tell students they are to prepare a short presentation of their data and how their precision was.

1 week later: Compile all student data on your own spreadsheet and show the class their results as a whole to show the relevance of the more data points compiled, the better the results should be; but again we are in science where things sometimes don't go as planned, which provides great discussion by the way! Water Data Table 07 Excel Pre & Post Data with % Error (Excel 119kB Aug13 08) Water Data table 07 Excel Pre & Post Data with % error & histograms (Excel 166kB Aug13 08) Water Data Table Blank (07 Excel) (Excel 11kB Aug13 08)

Teaching Notes and Tips

I just designed this activity in the 07-08 school year, so there are going to be a few bugs to work out. You may want to make sure to take the temperature of the water or solutions for the pre-instruction data as well.

Assessment

Give a short presentation of their data to the rest of the class and turn in a short writing on the possible sources of error for both the pre & post instruction data.

Standards

Standards Match:
  1. 9-12.I.B.3 Use mathematics and models to analyze and support conclusions
  2. 9-12.I.B.4 Identify possible sources of errors and the effects on results.

References and Resources