Experimental Error by Design

By Laura Hospitál on Dec 08, 2015

This activity is the result of a lab gone awry.  Students most often complete labs that have been set up to "work".  This is not how most real science often works and it is beneficial for students to have the opportunity to experience and research experimental error.


Set up a lab that won't work, but don't tell the students!
The Rate of Reaction Lab http://www.perkinselearning.org/accessible-science/rate-reaction-lab  was the lab that didn't work for me because I chose chalk that wasn't made of calcium carbonate.
If you choose this lab, buy sidewalk chalk (not usually made of calcium carbonate) for the experiment. See the materials section for more information. 


Depending on the lab chosen, the materials will vary.   If you choose to use the Rate of Reaction lab, the following is the list per lab group. Make sure not to buy chalk made of calcium carbonate.   Materials
  • vinegar – 100 mL
  • chalk – 2 small pieces- Crayola sidewalk chalk doesn't contain calcium carbonate while Crayola Anti-Dust White chalk does.  You can buy sidewalk chalk at toy, grocery, and drug stores while Crayola Anti-Dust White chalk is found at school and educational supply stores.
  • a mortar and pestle


After the students' lab doesn't work, ask the students to consider what might have gone wrong.  In the Rate of Reaction Lab, we all expected (including me) the chalk and vinegar to react.  When there is not any evidence of a reaction, ask the students to speculate what could be the case for this?  We considered the reactants (chalk and vinegar) and discussed the procedure.     Begin a discussion about experimental error.  Introduce the topic but tell students that in place of a lab report, they will write a brief report about experimental error based on research they do.  I required at least 50 words but this will depend on your students.   They should consider the following for their report.  
  • What is experimental error?
  • What are the various factors that can cause experimental error?
Post Lab: When students have turned in their reports and the instructor has has a chance to read them over, return to the topic briefly during class.  Focus on the fact that experimental error will cause inaccuracy in the results and that scientists must ALWAYS consider experimental error when analyzing and evaluating results.  Give examples from your experience or science projects your students have done.  Talk about the possibility of human error, equipment malfunctioning, etc.  


A lab other than the The Rate of Reaction lab could be used but set up the lab NOT to work (wrong chemicals, etc)  

NGSS Standards:

Middle School - Science and Engineering Practices
Conduct an investigation and evaluate the experimental design to produce data to serve as the basis for evidence that can meet the goals of the investigation. (MS-PS2-5)
Apply scientific ideas or principles to design, construct, and test a design of an object, tool, process or system. (MS-PS3-3)
High School - Science and Engineering Practices
Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models.  Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly. (HS-PS1-3)


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