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LAB_Osmosis Powered By Docstoc
					Name: ______________________ Date: ________ Class: ______

Under What Conditions Does Osmosis Occur?

Osmosis is the diffusion of water through a selectively permeable
membrane. There are three possibilities for the direction of water
     1.)        Water moves out; when water diffuses out of the cell, the
                cell shrinks, (weight loss). The solution responsible for this
                loss is called a hypertonic solution, which has a lower free
                water molecule concentration than the inside of the cell.
     2.)        Water moves in; when water diffuses into the cell, the cell
                swells, (weight gain). The solution responsible for this gain
                is called a hypotonic solution, which has a higher free water
                molecule concentration than inside the cell.
     3.)        No net water movement; when water diffuses into and out
                of the cell at equal rates, the cell stays the same size,
                (equilibrium). The solution responsible for this equilibrium is
                called an isotonic solution, which has the same free water
                molecule concentration as the inside of the cell.

You can observe the movement of water into or out of a grape under
different conditions.

     3 grapes
     3 small jars
     3 saran wrap pieces large enough to fit over top of jars
     3 rubber bands to hold saran wrap around lid
     1 saturated salt water solution (in a pitcher)
     grape juice
     tap water
     marking pen
     masking tape for labels
     paper towel
     electric balance
      1. Fill and label one jar with grape juice.
      2. Fill and label a second jar with salt water solution.
      3. Fill and label the third jar with tap water.
      4. Using an electric balance, find the mass of the first grape and
         place the grape into the grape juice jar, covering it with saran wrap
         and placing the rubber band around the lid to seal it. Record this
         grape’s mass in table 1 – 1, under Original Mass.
      5. Repeat step 4 for the final two grapes and their solutions.
      6. Once the experiment is set up, set the jars aside making sure you
         put your initials and class period on the masking tape used to label
         the solutions so you can find it tomorrow. It will now sit for 40
      7. Predict whether the mass of the grape will increase or decrease
         over the next 40 minutes. Record this prediction in Table 1 – 1,
         under Predicted Mass. Explain why you predicted this.
      8. After 40 minutes, remove each grape from its jar, and dry it
         gently with a paper towel. Using the electric balance, find its mass
         again. Record your results in Table 1 – 1, under Actual Mass.
      9. Clean up your materials.

TABLE 1 – 1
Solution       Original Mass   Predicted       Explain why   Actual Mass
                               Mass            the predicted
Grape Juice

Salt Water

Tap Water

   1. List the solutions in which osmosis occurred.

   2. How did you determine whether osmosis occurred in each of the three

   3. After noting the change in each of the grapes masses, label each
      solution as hypertonic, hypotonic, or isotonic.

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