Osmosis Lab Report
BIOL 120 Lab Week 9 - Osmosis
Introduction: In this experiment you will explore the effects of osmosis on eggs. An egg is surrounded by a semipermeable membrane and a hard shell. To observe the effects of osmosis the hardshell will first need to be removed.
In your kit Provided by you
distilled water 500 mL (about 16 oz) of acetic acid (vinegar)
gloves 4 eggs
graduated cups ¼ cup salt
125 mL (about 4 oz) of any other household liquid of your choice (ie applesauce, corn syrup, sugar solution, juice, broth)
one bowl
one plate
Part 1: Remove the outer hard shell of the eggs. Instructions adapted from Double Helix magazine.
Forty-eight hours ahead of your scheduled lab time you will soak your eggs in vinegar to dissolve the hard outer shell.
Egg shells contain calcium carbonate (CaCO3), and vinegar’s active ingredient is acetic acid (CH3COOH). When these chemicals react together you end up with a salt called calcium ethanoate, some water, and carbon dioxide gas. The reaction for this equation looks like this:
CaCO3 + 2CH3COOH → Ca(CH3COO) 2 + CO2 + H2O
Based on this chemical equation, what do you think will happen to the hard shell of your eggs while the egg is soaking in vinegar? I think it will dissolve. DAY 1 - 48 hours before Lab
1. Put the eggs in the large bowl.
2. Pour vinegar into the bowl until the eggs are completely covered. The eggs will start to bubble.
extra cup for mixing
large spoon (ie soup spoon)
tapwater
Paper and marker to label
3. Leave eggs overnight.
You should notice that the eggs are bubbling. Based on the chemical equation for this reaction provided above. What do you think are the bubbles? DAY 2 - 24 hours before Lab
4. At this point the hard outer shell on your egg should have started to dissolve, and your egg may feel soft to the touch. You can rinse the eggs under the sink faucet and gently rub away remaining shell. If the shell does not rub away easily, your eggs are not ready.
5. In order to be ready for the experiment your outer shell must be completely
dissolved and the yellow yolk be visible as seen below. If your egg is not as pictured below, and the bubbles have slowed or ceased, you must replace the vinegar with fresh vinegar (proceed to step 6). If your egg is ready, you may place it in the fridge until it is time for lab and now proceed to step 7.
6. Gently drain the old vinegar out of the bowl into your sink. Cover the eggs with fresh vinegar. Continue to let soak until the hard outer shell is completely dissolved. Once the eggs are ready, you can rinse them with water and keep them in the fridge until it is time for lab.
7. While you’re waiting, create a saturated salt solution in your extra by dissolving as much salt as you can into 125 mL of the distilled water from your kit (measure because you’ll need the remaining distilled water for day 2). Keep adding salt until a few salt crystals are left on the bottom that will not go away, no matter how long you stir.
Day THREE - Lab Day:
1. The eggs should be soft and squishy. Remove from the vinegar and gently rub any remaining shell off the egg with your fingertips until you can see the yolk through the membrane (clear covering). You can gently place the extra eggs on your plate while you measure the volume of each in the next step.
2. You will next measure the volume of each egg using displacement. Fill one of
your graduated cups to the 150mL mark with tapwater.
3. Add the egg. Note the new volume: _____________
4. Calculate the volume of the egg
New volume - 150mL = ___________ Gently place the egg on your plate. Use a piece of paper or tape to label the egg #. Repeat for each egg, making sure to fill to 150mL mark before you add the egg. Table 1. Egg volumes at Timezero
5. Next empty the graduated cups. Label the cups as follows
Cup 1: Control Cup 2: Water (hypotonic) Cup 3: Salt (Hypertonic) Cup 4: Home solution (unknown tonicity)
Egg 1 Egg 2 Egg 3 Egg 4
Egg volume 90 95 100 90
Make a prediction for each cup. What do you think will happen in each cup? Which direction will water move? What will happen to the volume of the egg? Table 2. Predictions
Now that you have written your predictions write a 1-2 hypothesis that includes the scientific principle being tested (osmosis) and your predictions. It may be helpful to think about your hypothesis as an “if…. then” statement. For example “If scientific principle is occurring, then prediction will happen” I predict that if the solution is hypertonic then the egg will shrink and vice versa.
6. Next prepare your treatments. Leave cup 1, control, empty. Add egg #1. 7. Fill cup 2 with 125 mL of distilled water. Add egg #2. 8. Fill cup 3 with 125 mL of the salt solution you prepared yesterday (make sure it is
well stirred). Add egg #3. 9. Fill cup 4 with 125 mL of your unknown tonicity solution. Add egg #4. 10.Leave eggs overnight (at least 24 hours). 11.Take each egg out of their cup one at a time and measure the final volume using
the same displacement method to measure the original volume (fill cup to 150mL mark and then add egg, measure new volume).
New volume - 150mL = final egg volume
Cup Prediction (write a sentence including the direction of water movement and final egg volume)
Control (no liquid)
The water will remain where it is and vol should remain 90
Water (hypotonic)
Water will move in the egg and vol 115
Salt (Hypertonic )
Water will move out of the egg and vol. 75
Home solution (Unknown)
Water will move out of the egg and vol. 60
*If for some reason your cup overflows you will need to use a larger container for the displacement. 12. Then calculate the change in volume and your visual observations. Final egg volume - Original egg volume = Change in volume Table 3. Egg volumes at TimeFinal
Discussion Questions
1. Did your eggs change in size? yes
2. Did the physical appearance of the eggs change? Yes one of then turned red
3. Did any eggs stay the same? yes
4. Did your results match your predictions? yes
5. Based on your results what can you conclude about the tonicity of your unknown solution relative to the egg?
My unknown solution was hypotonic
6. Do you think the egg's inner membrane is selectively permeable? Why or why not?
Yes it is because water moves through the membrane easily.
Egg 1 Egg 2 Egg 3 Egg 4
Final egg volume 90 120 80 110
Change in volume no yes yes yes
Observations Stayed the same
Got bigger shrunk Red, got bigger