We all teach about Raoult's law and the positive and negative deviations from ideality, but showing such effects in the lab have been difficult. We have found that precision surface tension measurements demonstrate this effect nicely and have developed a laboratory for students to see this for themselves. Commercial equipment for contact angle measurement and pendant drop proved insufficient for precise determination of surface tension of mixtures and so we constructed an inexpensive system that can be 10X more accurate and precise.

Nonlinear deviations from ideality in surface tension: A practical PChem experiment

245th National Meeting (2013)

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