Saturday, November 5, 2011

Making Water

The base is in the 1-L volumetric flask.

Adding the acid to the base
More than 1 liter here!
Shakhashiri has all the answers.  I like to do the demonstration of a neutralization reaction with equal volumes of hydrochloric acid and sodium hydroxide.  The reaction produces salt and water.  If you mix 500 milliliters of 2-molar solutions of the acid and base, you will produce 18 mL of water (1 mole).  I learned about this demo at ChemEd, a great conference for chemistry teachers.  In previous years, I used a 1-liter graduated cylinder, my favorite demonstration glassware, for this reaction.  Although it always worked, the additional volume of water was very difficult to see.  Shakhashiri has a description of this same demo in volume 3, Demo 9.17, with the solution to my problem.  He uses volumetric flasks!  Of course!  Today, when I combined the 500 mL of acid and base, both made up in 500 mL volumetric flasks, the additional water was easily visible in the neck of a 1-liter volumetric flask.  I added some universal indicator to the acid and base solutions to give the demo some color.  This was an extra bonus because the two solutions formed layers when I poured them together the 1-Liter flask.  We all enjoyed the interesting effect of the blue and pink layers.  When I mixed the flask, the volume increase caused pressure to build up in the flask and the stopper popped off a couple of times.  Overall, the Demo was a great way to show the products of a neutralization reaction, including the often-overlooked water molecules that are formed.
Releasing the pressure.
Admiring the interesting layers.

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