4. Diffusion & Osmosis - Don't Stop Movin' (Part 1)

  DIFFUSION: Molecules are always in constant motion, and tend to move from a place of higher concentration to another with lower concentration. And the net movement of those molecules are called diffusion. The diffusion can occur in gas, liquid, or through solids. One example of diffusion is that when a bottle of perfume is opened, within minutes people in further distance can smell the perfume.

  OSMOSIS: Osmosis is a type of diffusion. However, it is special as well since it involves a selectively permeable membrane in the transport. The membrane allows certain molecules to pass through to the place with lower concentration, while it restricts the movement of others.

  TYPES OF SOLUTION BASED ON SOLUTE CONCENTRATION:
  If the solution in the bag has lower concentration than the solution in the beaker, the solution in the bag is hypotonic to the solution in beaker.
  If the solution in the bag has higher concentration than the solution in the beaker, the solution in the bag is hypertonic to the solution in beaker.
  If the solution in the bag has same concentration as the solution in the beaker, the solution in the bag is isotonic to the solution in beaker.

  WATER POTENTIAL: Water potential is the tendency of water to move from the place of higher concentration to another with lower concentration. It is affected by the pressure and the amount of solute.
 
  According the 1st lab we did today on diffusion and osmosis, we made 6 small packs ("cells") of 7 ml of solutions in different molarities.

  After we dried and massed all the 6 cells, we placed each of them into a labeled cup, which contained 50ml of distilled water.

  We let them stay for 30 minutes. After taking them out of the cups, we re-massed the cells and calculated the percent change in mass to find out the molarities.

  The 2nd lab we did today was based on diffusion and osmosis as well. However, instead of using "cells" of different solutions, we used russet potato. We cut 24 pieces of russet potatoes into roughly same size. We massed every 4 pieces of potatoes before we put them in each labeled cup.

  Later, we put 25ml of each solution into each labeled cup, and after we covered the top of the cups, we let them stay for about 9 hours. Then after we took the potatoes out of each cup, we re-massed them and calculated the percent change in each cup.

-Andy Liu'15