Osmosis

Students applied inquiry skills by performing 3 tests using iodine, biuret’s reagent, and benedict's solution. After adding these reagents, students concluded that starch was the mystery substance in the bag because iodine caused a color change from brown to blue-black when it came in contact with the substance inside the bags. When students added buiret’s and Benedict's reagent, there were no color change, indicating that the substance in the bag was not a protein or glucose. Students concluded that the bag was a dialysis bag because molecules small enough to pass through the tubing moved into the bag in the direction of low concentration. Dialysis maximizes the concentration gradient in effort to achieve equilibrium. The indication of starch allowed students to visualize the high concentration of iodine moving to the low concentration of starch creating the blue color. In this experiment, there were several opportunities to make an error. If there was a leak or tear where the tubing was twisted shut, the mass of the bag would be inaccurate. If the student managing the dialysis bag accidentally touched the portion of the tubing that serves as the semipermeable membrane, the oils from their fingertips could have blocked the pores and holes, maki ng the data invalid. If the bag contained residue from the water it was submerged in, the mass of the bag would increase and be imprecise. A suggestion to eliminating this error is to gently dry the bag with a paper towel after taking it out of the beaker. This experimentation serves as an exceptional example of the use of inquiry in scientific settings. Without inquiry skills such as observation, inference, prediction, classification, and communication, students would not be able to distinguish the substance inside the bag and correspondingly, what the bag was.