Measuring Adsorption Isotherm

When we prepared the solutions of known concentration for the calibration curve, we weighed the powder only once and diluted to get the other concentrations. For the adsorption experiments, we again weigh the dye only once but make up enough solution for all the tests. Let's say that the stock solution will contain 2 g/L of dye. We sprinkle some powdered dye into a plastic dish that fits on the analytical balance and find that we have 1.772 g. This is added to a volumetric flask of 1 liter size and di luted to the mark with water.

Now we use ordinary Ehrlenmeyer flasks of a convenient size, 250 ml should be about right. Into each we add portions of carbon that have been weighed carefully. Then 100 ml of stock solution (1.772 g/L) is added to each flask. One flask that serves as a control has no carbon. The flasks are placed on a shaker and left shaking as long as possible because adsorption can be slow. We hope to reach equilibrium.

At the end of the run, each flask is analyzed for dye using the colorimeter and the calibration curve. The results are: 

Flask #    Grams of Carbon   Concentration of Dye
  1                 0                  1.768 g/L
  2                 0.58               1.416
  3                 1.288              1.062
  4                 2.21               0.711
  5                 3.71               0.419
  6                 5.26               0.178
  7                 9.81               0.042
Go "with the flow"

 Home page for adsorption

Done

 Last update 10-Jan-95