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Sig Figs, Units, Scientific Notation and other time consuming stuff

August 25, 2006

Well, I’ve been at school for a week now and as usual there is a colossal amount of stuff to do and it’s very hectic as we try to get the year off to a good start. In terms of teaching AP, I feel that a fast start along with the setting of VERY high expectations & goals is absolutely crucial. This does a couple of things; firstly it sets the tone, and secondly it helps the kids see AP Chemistry as different to the other subjects they are studying. By emphasizing the fact that quite literally from day one we are focusing on the AP exam, they get a tangible goal that is often lacking in some other classes. Don’t get me wrong, great things are happening in other classes, but sometimes academically immature sophomores don’t quite appreciate the value of those other things and their attitude is a bit more passive! Given that this is their first AP class and they have NO background in chemistry we have to instill a sense of urgency and drive. In AP chemistry I want there to be no doubt about why we are here and what the goal is.

In light of the need for a blistering start to the year, I find myself constantly frustrated by the relative triviality of my TOPIC 1 – Matter & Measurement. It seems as though sig figs, units, scientific notation and all that “math” stuff should either be taught ONCE in a science context, or perhaps not at ALL by scientists and left to the math folk. A few years ago I completely gave up teaching the stuff in TOPIC 1, and I went ahead and started assigning it as homework’s and test preparation on day one. We have a TOPIC 1 test, a few days into the year. Even by doing that, the constant (largely irrelevant) questions about the confusion over sig figs (they’ve heard it three or four times form different teachers with slightly different rules and expectations by the time they get to me) serve to distract the kids from FAR more important chemistry issues. I find the whole thing a real anchor working against me.

I think the solution is what I have said above – teach it ONCE in a ninth grade science class, or not at ALL and liaise with the math department so they can carry the burden. Even though this is review for many kids it hampers my momentum at a very important juncture.


  1. MrB

    I agree that students are confused about sig fig. In addition to only teaching it once in ninth grade, the library should provide programmed materials that would review or even teach this topic and other necessary but basic topics.

  2. waterman

    I agree 100%. Do not teach SF. I do not teach SF at all. I teach students to round ALL their answers to three numbers, regardless of where the decimal is. The AP exam accepts plus/minus one SF so that technique covers two, three and four SF. If the correct answer falls out of that range and it rarely does, students lose 1 point of 160 raw points.
    As for the MC question regarding SF, I treat it only when students ask about such a question on a practice exam. Then and only then, are they ready to learn it. So I spend two to three minutes covering how to treat SF when performing mathematical calculations. The ones who get it, get the question right. The ones who do not understand fully, probably make a pretty good guess. If they don’t, they lose only another 1 point out of 160. Let’s teach students chemistry!
    Ed Waterman

  3. scoulombe

    I agree to a point, I prefer to teach it in the context of an actual lab. I have a density lab and they have to “see” what a significant digit with a label is. How to estimate to one place after the indexed scale. They can see why when you find the mass of a small piece of lead vs a large piece you get more sig figs and more precision etc. I too am spending less time on it. I don’t know what to do about sci not, I tried getting them to all use the same calculator. They get the order of operations mixed up.


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