Significant figures on the AP Chemistry exam

March 19, 2015
Categories: 2013-14 Curriculum | AP | Unit 0

What’s the deal? Good question! As far as I am aware (happy to be corrected), there has never been a clear, written policy on this matter from the College Board – yet ANOTHER failure to communicate; AP Chemistry Czar anyone?

However, there was a ‘unwritten’ and ‘understood’ rule in place for many years, that a random question would be selected on the exam, where the ‘rules’ regarding significant figures would be tested, and that only one point would be at stake across the whole AP exam. In addition, anecdotal evidence suggested that there was a tolerance of +/- on the correct number of significant figures. For example, no point would be deducted for an answer that SHOULD have had three significant figures, if the student wrote two, three or four sig figs. As a result, the common (sensible) advice from chemistry teachers was usually, ‘simply write three sig figs in your answer, and the likelihood is that you won’t lose any points’. This whole situation was thought to be ‘understood’, since anecdotal evidence from graders supported it, as did scoring standards.

5698345_sThen, suddenly, completely out of the blue, and with no announcement circa 2008 (it may have been Q2 in 2008 but I am not sure about that), it turned out that the EXACT number of significant figures had to be used on a particular question, and that the tolerance was (apparently) torn up. Again, still no official word.

It’s a mess, and the fact that we are left guessing is another example of the CB’s ambiguity and IF the CB is going to persist with the loss of even a single point on the exam for ‘incorrect’ sig figs, then ‘we’, as teachers and students, have an absolute need/right to know what the policy actually is.


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