Turn on a Spectronic 20 and warm it up for at least 15 minutes. Be sure the wavelength is set to 540nm. When the instrument has warmed up, use a clean small test tube from the drawer filled 2/3 with the first NaOH solution that is planned to use, as a blank set 0% and 100% transmittance.
Take a %T reading every minute for at least 15 minutes so it may be convenient to wait until the room clock’s second hand approaches 12 before beginning the following procedure. Add one single drop of the crystal violet dye solution, invert to mix the contents of the test tube, and carefully place the tube into the instrument. When the drop hits the surface is your “time zero”, and one minute later you will begin taking readings of %T. Leave the sample tube in the instrument throughout the data collection process. Obtain readings of %T every minute for at least 15 minutes. Record %T values to one decimal place, as this allows you to convert to absorbance and retain three significant figures.
When the 15th and final reading has been taken, remove the sample from the instrument and prepare to re-zero the instrument with a new NaOH blank in another test tube. Then repeat the entire 15-minute data collection a second time.
After this is all finished, turn off the instrument, discard the samples down the drain, and carefully clean the test tubes used.
The disappearance of the purple color indicated the consumption of the crystal violet dye. As the reaction proceeded, the color would fade and more of the incident light would be allowed through. In this experiment the percent transmittance increased as time passed by. The percent transmittance was converted to absorbance, and it is directly proportional to concentration, and our data sets were of absorbance versus time. The abrosbances were treated as if they were actually concentrations of the crystal violet dy...