This experiment takes a qualitative approach to equilibrium chemistry, studying Le Chatelier’s principle as it applies to the synthesis of bio-based ink.
Students performed experiments in 3 separate investigations. In the first, they mixed copper sulfate and sodium carbonate, and then added vinegar to the mixture to study solubility rules and precipitation: a blue solid, copper (II) carbonate formed. In the second, they studied acid-base equilibria by creating a color gradient using indicators and solutions of various pH. They then use the gradient to identify the pH of an unknown solution. The third investigation dealt with redox equilibria: manipulating the equilibrium of oxygen to synthesize a bio-based ink from iron sulfate, tea/oak galls, ascorbic acid, and hydrogen peroxide.
This exercise gave students a chance to see the applications of equilibrium chemistry, rather than just mixing various solutions and waiting for precipitation. It demonstrates the Green Chemistry principle s of renewable feedstocks. It is also a greener alternative to traditional experiments that use heavy metals like Cd, Pb, Hg, and Cr.
Summary prepared March 2012 by Swetha Akella at the UC Berkeley.
Douskey, M. Equilibrium investigations and the synthesis of a biobased ink, College of Chemistry, UC Berkeley, 2012