We’re Only Human…

Using a buret helped to minimize error in these standard solutions.

Experimental error is always a challenging concept to teach high school chemistry students. I can imagine what goes on in a student’s mind when they get to the section of the conclusion where they must discuss experimental errors. One student thinks, “Hmmmm, I might have done my calculations wrong, that must count as experimental error. After all, it’s an error and it relates to my experiment. Yes, I’ll write about that!” And another student ponders the meaning of life with this thought, “We all make mistakes, it’s just human nature. No one is perfect, so why should I expect my lab to come out right. Human error must be my most significant source of error in this lab. If I write that, then I’ve covered all the bases. Enough said.” And then there’s the classic, “I must have read the graduated cylinder wrong, which led to my final answer for number of moles to be off. That sounds scientific and we must have used a graduated cylinder at least once today.” These thoughts get translated into an error analysis that doesn’t actually say anything meaningful and sheds very little light on the quality of the experimental results.

The “human error” statement is one that has deep roots in our science students. I encounter it nearly every time I collect a set of lab reports, even after I tell them to NEVER write that meaningless phrase in their labs. Chemistry students just can’t seem to help themselves. It must feel so satisfying to write and somehow make them feel like they are being very thorough. When I bring this up at department meetings, my colleagues are as perplexed and annoyed by the “human error” phrase in lab reports as I am. The freshman teachers promise that they aren’t instructing their students to write it, and activity discourage it. I know that the effort I make to eradicated “human error” from lab reports does not completely worked. This week I was shocked to learn that even chemistry majors at Boston University write “human error” in their lab reports. Really?! Maybe they think that college professors are finally able to fully appreciate their philosophical approach to error analysis that is lost on their high school instructors. I’m sure that college professors must think that we are telling student to always include that phrase as a “catch all” for anything that they couldn’t think of at the time of their lab report writing. Let me make this clear to everyone: students just can’t give up on human error, no matter how many ways we tell them that it doesn’t work.

So what do I tell my students when they ask me, “If I can’t blame all my bad results on human error, then what should I write about in my error analysis?” The first place to look is the chemistry. I try to get my students to think through the chemical reaction/system for factors that might take away from the desired outcome. The tricky part about the error discussion is that high school labs usually work pretty well, we don’t have time for experiments that are duds. The next thing I tell them is to look at their data chart. I challenge them to think about things they did (or didn’t do) that would change the data they recorded in during the lab, beyond misreading the graduated cylinder. Ultimately, my goal is to get me students to think critically about their observations and make some decisions about the quality of their work without falling back on broad “hand waving” statements like human error.