In all cells, survival depends on the ability to maintain homeostasis by regulating the movement of molecules across the cell membrane. In osmosis, water molecules move across a selectively permeable membrane toward a solution with a higher concentration of solutes. The molecules continue to move until equilibrium is reached (that is, equal concentrations of water molecules and of solute molecules on either side of the membrane).
The concentration of solutes in water is low or nonexistent. Therefore, water is hypotonic to the fluid within the corpuscles. If human red blood corpuscles are placed in water instead of blood plasma, water will enter the corpuscles until they swell, burst, and die. If the corpuscles are placed in a solution with a high concentration of solute compared to the corpuscles, water will pass through the cell membranes into the surrounding hypertonic solution, and the corpuscles will shrink, or plasmolyze.
The selectively permeable membrane you will use to study osmosis is the membrane within an eggshell. It allows water to pass through in response to concentrations of the solutions on either side of the membrane. The water will move toward the more hypertonic, or highly concentrated, solutions.

PRE-LAB PREP:

You should be able to buy 1 molar hydrochloric acid solution. If you can not, then mix 2.2 ml of concentrated hydrochloric acid with enough distilled water to make a total volume of 25 ml. (REMEMBER: NEVER ADD WATER TO ACID, ALWAYS ADD ACID TO WATER.)

MATERIALS:

Safety goggles
Balance 400-mL beaker
Raw egg 250-mL beaker
Spoon
1molar Hydrochloric acid(HCl)
Karo syrup, undiluted
Paper towels

PROCEDURE:

1. Determine the mass of a raw egg to the nearest 0.01 g. Record the mass as mass of raw egg and shell in the DATA TABLE.

2. Put on your safety goggles. Place a 400-ml beaker on several sheets of paper toweling. Carefully place 250 mL of HCl solution in the beaker. CAUTION: HCl will burn if spilled on your skin or clothing.

3. Using a spoon or tongs, carefully place the egg into the HCl solution. Place a 250-mL beaker half full of water over the egg to keep it submerged . Wait 15 minutes and record your observations.

4.Over the sink, remove the egg with a spoon and rinse it well under tap water. Also rinse all glassware to remove the acid.

5. Place the egg on a paper towel and CAREFULLY blot it dry. Find the mass of the egg and record it in the DATA TABLE as mass of egg without shell.

6. Place the egg in a 400-mL beaker. Pour water into the beaker so that the egg is completely covered. Wait 20 minutes. Record your observations.

7. Remove the egg from the beaker using a spoon. Place the egg on a paper towel and CAREFULLY blot it dry. Find the mass of the egg and record it in the DATA TABLE as mass of egg after 20 minutes in water.

8. Now place the egg in a 400-mL beaker and cover it with Karo syrup. Observe the egg in the syrup after 20 minutes. Record your observations. Place the beaker and egg in a safe place for 24 hours.

9. The next day, remove the egg from the Karo syrup, rinse, and blot. Find the mass of the egg and record it in the DATA TABLE as mass of egg after 24 hours in Karo syrup. Record your observations.

DATA TABLE:

Mass of raw egg and shell. ________ g

Mass of egg without shell. ________ g

Mass of egg after 20 minutes in water. ________ g

Mass of egg after 24 hours in Karo syrup. ________ g

QUESTION 1. What effect did the acid have on the egg?

QUESTION 2. What passive process of moving molecules is demonstrated in this experiment?

QUESTION 3. In which instance is the egg in a hypertonic solution?

QUESTION 4. In which instance is the egg in a hypotonic solution?

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