Osmosis

 

We are going to see how water move through the membrane of a cell (a raw egg) when it is placed in solutions with different concentrations of water.  The egg has had its shell removed by placing it in vinegar.  BE CAREFUL!!  Do not break the egg.

 

Materials:  Fill in the materials while your egg is in the first solution for eight minutes.

 

Procedure:

            1.  Gently dry the egg.  Then measure and record its mass.

            2.  Place the egg in 20% salt for 8 minutes. (Make your data table and fill in the materials.)

            3.  Dry the egg and find and record the new mass.

            4.  Place the egg in 5% salt solution for 8 minutes.

            5.  Dry the egg and find and record the new mass.

            6.  Place the egg in distilled water for eight minutes.

            7.  Dry the egg and find and record the new mass.

            8.  Return the egg to the teacher.

 

Data:

            Make a table for your data.

 

Analysis:

            Find the change in mass of the egg while in the 20% salt solution.

             

                Mass of egg after 20% salt             If this number is negative, be sure you

              -Mass of egg at start                         record the negative sign to show that the egg lost mass.  If the number is positive record the positive sign to show that the egg gained                                                                                                        mass.

 

            Find the change in the mass of the egg in 5% salt solution.

             

              Mass of egg after 5% salt

            -Mass of egg after 20% salt

 

Find the change in the mass of the egg in deionized water.

           

              Mass of egg after DI water

            -Mass of egg after 5% salt

 

Conclusion: 

1.  Describe what happened to the mass of the egg as it was placed in each solution.

 

2.  Define osmosis.

 

3.  Explain each change in mass based on the concentration of water in each solution.

 

4.  Predict what would happen to the egg if it were left in deionized water overnight.
Osmosis

 

            Water is the most abundant substance in any cell.  All of the chemical processes of the cell involve water in some way.  Water passes into and out of the cell by osmosis.  Osmosis is the diffusion of water through a semipermeable membrane from where the concentration of water is high to where the concentration of water is low.

            The cell membrane is a semipermeable membrane.  It allows some substances to pass through while blocking others.  Because water molecules are relatively small, they easily pass through the cell membrane.  If the cell is in an environment where the concentration of water molecules is greater outside than it is inside, water will move through the membrane and into the cell  by osmosis.  If the concentration of water is greater inside the cell than it is outside, the water will move out of the cell by osmosis.

 

  

 

 

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