Shouldn’t it be blue?

I love how people think, and I love teachable moments.

We were using extracted red cabbage juice as a pH indicator today, and a student came to ask what he should do if he made a mistake. I asked what had gone wrong, and he said “Something happened with our strong base sample. It’s yellowy green, but it should be dark blue”.

Since this was the part of the lab where we were observing what the colours were, I asked him why he thought it should be dark blue. His reasoning went like this: neutral is purple, mild acid (pH=3) was light pink, strong acid (pH=1) was red. Mild base (pH=9) was blue, and therefore, strong base should be dark blue. Rather than simply correct his misconception (which was, after all, a hypothesis based on extrapolation), I simply had him take another sample.

His result? Yellow green. He faced a pre-conception head on, verified for himself his results, learned that double checking results is valid, and that things can sometimes – but not always – be extrapolated. Lots of learning from one little transaction. Yay science!

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