I have used the Buffer Solutions experiment three terms now, and each term, at least one of the solutions gets all the way to 25 drops of added HCl or NaOH (or both) without the pH ever changing by more than 0.5 units after each addition. In practice, this means that the buffer capacity is at least 25 drops, but if a student puts 25 drops in, it is counted incorrect. By trial and error, we have discovered that the only answer that is counted correct is 0 drops, which is completely absurd! Looking at the "correct" answer in a student's report, I see it says the buffer capacity is NaN (which I assume means it isn't defined). This is a programming bug that needs to be addressed. Please change it so that it will accept 25 drops as the buffer capacity in those situations. That will at least make the trends more apparent.
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