Reference no: EM132633100

Laboratory Exercise

Osmosis and Diffusion

A. Introduction  Osmosis

The purpose of this lab is to provide a hands-on demonstrate of the concepts of diffusion and osmosis to students. is the diffusion of water molecules through a semi-permeable membrane.  This is how water and other small chemical substances get into and out of our cells. In this lab we will investigate the effects of different solutions on the water content of an ordinary egg, which will serve as our model of a cell.

Remember, when comparing 2 solutions, the one with the greatest amount of substance dissolved in it (the "solute") is called hypertonic, while the one with the lesser amount of a solute dissolved in it is called hypotonic. Therefore, hypertonic solutions have less water (and more solute) in them than hypotonic solutions (which have relatively more water, less solute). Water, like most substances, will try to move from an area of greater concentration to one of a lesser concentration. If allowed to move freely, most chemicals will try to evenly distribute themselves in a solution. So if you were to mix a hypertonic and a hypotonic solution together and allow them to sit for a while (or if you stirred or mixed them together) eventually a single isotonic (which mean equal) solution would form. So when you add dry sugar (a hypertonic solution although there is very little water in it) into your tea (a hypotonic solution) they will mix eventually. But who has time to wait for that?! So we stir the sugar in to get it to dissolve and distribute into solution faster. Are these concepts clear now? If not, let me know.

B. Materials and Methods

In this experiment you will observe the movement of water into and out of an egg. we will remove the minerals from the egg shell leaving only a membrane that is permeable to water. This experiment takes 5 days minimum to complete. START EARLY! Follow the directions below to observe the movement of water into and out of an egg. Please answer all of the questions within the results section (Part C) which will guide you through the final online lab report.

1. Supplies needed: 3 eggs; 4 drinking glasses or clear containers; vinegar (about 2 cups); foil or plastic wrap; white Karo syrup (or any brand of heavy corn syrup); water.

2. Place the eggs into a container and cover them with vinegar. Cover the container with foil or plastic wrap and set it in the fridge for 3 days. The vinegar is an acid (which you already know from a previous lab) and it will dissolve the minerals in the shell so that the eggs will become very soft. So handle carefully - you really only need 2 eggs, the third one is an extra in case you didn't believe me on how soft they will be! Observe and photograph the eggs daily and note any change in shape or size you see for the report. After 3 days remove the eggs from vinegar and gently rinse with tap water. Discard vinegar and rinse container.

3.  Put each egg into a clear glass and cover completely with Karo/corn syrup. Let egg sit for approximately 1 day. Based on knowledge of chemical solutions, form a hypothesis for your report as to what you think will happen to the eggs in the syrup. Observe and photograph any changes in the eggs.

4. After 1 day remove the eggs and rinse gently with water then completely cover with water in a clear cup. Form a hypothesis as to what you think will happen to the eggs in the water and let sit for 1 day. Observe and photograph any changes in the eggs. Make sure you take one good selfie showing yourself and the final state of the eggs. After this step you may discard the eggs and clean up the experiment.

C. Laboratory results

DIRECTIONS: Answer these questions based on your observations and conclusions from the egg experiment. Use these to answer the questions within the online lab report.

1. What did you observe happening to the eggs as they sat in vinegar, syrup, and water?

2. Was syrup hypertonic or hypotonic compared to the fluids in the egg in step 3? Why?

3. Was water hypertonic or hypotonic compared to the fluids in the egg in step 4? Why?

4. APPLICATION: If a shipwrecked sailor drinks sea water, he will probably die. Why is salty seawater not drinkable?

5. APPLICATION: If a bowl of fresh strawberries is sprinkled with sugar, a few minutes later the berries are covered with juice. Can you explain why?