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Summary
In this lab, students use different types of laboratory glassware to measure 50 mL of water and determine the accuracy of each piece of glassware.
Grade Level
High school
Objectives
By the end of this lesson, students should be able to
- determine the accuracy of different pieces of glassware.
- explain why some pieces of glassware produce better accuracy than others.
- calculate percent error.
Chemistry Topics
This lesson supports students’ understanding of
- Accuracy
Time
Teacher Preparation: 10 minutes
Lesson: 60 minutes
Materials
For each group:
- Beaker
- Erlenmeyer flask
- Graduated cylinder
- Volumetric flask
- Burette capable of measuring exactly 50 mL
Safety
There are no special safety considerations for this lab.
Teacher Notes
- As long as each piece of glassware is capable of holding 50 mL, the exact size is not important.
- If groups have different sized beakers, flasks, and cylinders, discuss which size was the most accurate and why.
- When measuring the mass of water from the burette, have students use a separate beaker to hold the water, since the burette will be difficult to place on the scale.
For the Student
Lesson
Purpose
To determine which piece of glassware provides the greatest accuracy when measuring a 50 mL sample of water.
Materials
- Beaker
- Erlenmeyer flask
- Graduated cylinder
- Volumetric flask
- Burette capable of measuring exactly 50 mL
Procedure
- Obtain one clean & dry beaker, Erlenmeyer flask, graduated cylinder, volumetric flask and burette capable of measuring exactly 50 mL.
- Tare (zero) the balance.
- Place the beaker on balance. Record tare mass of beaker below.
- Fill test beaker exactly to the 50 mL line with water. Record mass of H2O plus beaker.
- Repeat steps three and four for each of the other pieces of glassware and record readings below.
Note: use a different beaker and obtain tare mass for vessel to hold the 50 mL sample from the burette.
| 50 ml H2O from: | Tare (g) | Total Mass (g) |
|---|---|---|
| Beaker | ||
| Erlenmeyer Flask | ||
| Graduated Cylinder | ||
| Burette* | ||
| Volumetric Flask |
Analysis
- Why can you use a known volume of water to decide whether or not glassware is accurate?
- Do the same sizes and types of glassware have the same tare mass? How do you know?
- Calculate the mass of each 50 mL water sample by subtracting the tare mass from the total mass.
- Calculate the percent error for each type of glassware tested. The actual mass of 50 mL of water is 50 g.
- List the glassware in order of the most accurate to the least accurate. How were the rankings determined?
- Why does some laboratory glassware have a large percent error?
- List at least two sources of error for this experiment.
- How could this experiment have been improved?