Author: Jon

The secret area in acid-base titration

With phenolphthalein (in 50% EtOH) as the indicator, and base as the titrant, it is common knowledge that the solution turns from colorless to magenta.  However, with careful sub-drop addition, the solution actually first turns milky-white, then milky-pink, before it clears up to a transparent pink at the end point: After learning about the existence of the “secret area”, many students did the titration with utmost care.  It was fun (and pretty tense) to watch. Chemistry-wise I am not too sure what is precipitating.  (Both the acid / base forms of phenolphthalein should be completely soluble.)  Surely I am...

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Van der Waal Equation / Ideal Gas Law Explorer

See the Pen Vue / graph.js – VdW eqn exploration by Jon Chui (@jkwchui) on CodePen. The ideal gas equation PV = nRT assumes an ideal gas of which the individual gas molecule has no attraction for another gas molecule, occupies no volume of its own. Real gases do not obey the Ideal Gas Law at some conditions, and their deviation can be corrected by using the Van der Waal equation instead.  In the VdW equation, an attraction constant a and a volume constant b is introduced to account for the two above properties of real gases. A curious and diligent student revised over summer and asked about the VdW equation.  I tried to answer Matthew’s queries to the best of my ability (which isn’t much.  Sadly, after years with Tom Fyles I haven’t developed the taste or acumen for physical chemistry).  While doing so, I realized that a list of measured VdW constants is easy to find, but visualizing how this correction impacts the P-V isotherm is not available.  So I built one. I used Vue.js for the two-way binding and reactivity, bulma for styling, and chart.js for graphing.  Panning and zooming used the Pan/Zoom plugin for chart.js.  I tried plotly.js for graphing but I could not get the reactivity to work.  Actually, I still don’t understand many aspects of the reactivity: somehow if the display of the array...

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Our New Assessment Calendar

Background Historically at LPCUWC we centralize student assessments on a paper calendar in the Staff Room.  Not all assessments were consistently updated, testing conflicts were seen but unresolved, and its utility has been limited.  In May 2015 our Director of Studies asked me to look at the a spreadsheet that would be the assessment calendar for the new year.  Over a weekend I shaped the Sheet, making it easy to work with and easy to maintain, and layered with functionalities that help both teachers and students.  This is the corresponding How-to Guide, designated for students and teachers. Even though this was designed...

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