Life Science Curriculum 8-12
Submitted by: Kristen Stoermer
Institution: Azusa Pacific University
Title of Experiment: Why Things Float Better in the Ocean
- 6 raw eggs
- 6 identical drinking glasses
- table salt
- a teaspoon
- a small scale
- graduated cylinder
Scientific Background of Experiment:
Density is described as a substance's mass per unit volume. Everything has a different density, and that density affects other properties of the substance. For instance, a liquid's density will determine how well objects are able float or sink in it. This lab will look at the differences in the density of salt-water and freshwater, and the effects that has on an object's ability to float in each. The difference in the densities should show us why things float better in seawater, as opposed to their sinking in freshwater. The fact that seawater has salt dissolved in it makes things more able to float in it. The salt in seawater causes it to weigh more per unit volume than freshwater. The higher weight causes saltwater to have a higher density, as density is directly related to the mass of the substance. Also, different amounts of salt will have different affects on the density. That is why we will use a variety of amounts of salt in this lab, to see the gradual changes in an egg's floating ability as it corresponds to the density of the water it is in.
1. Put 400mL of water into each of the two glasses.
2. Add five heaping teaspoons of salt to one of the glasses. Mix until the salt is dissolved.
3. Carefully put one egg in each glass, and observe what happens to each egg.
4. Now, take the eggs out of each glass, and weigh them. Compare your results with the observation you made before.
5. Now fill the other four glasses with 400mL water. Add one heaping teaspoon of salt to the first glass, two to the second, three to the third, and four to the fourth. Mix each glass thoroughly.
6. Now line up all six glasses that you have, in order from the one with the most amount of salt added, down to the glass with no salt.
7. Place an egg in each of the glasses, and observe the position of each egg in its glass.
8. Using your observations, guess which glass of water has the greatest density. Now, remove the eggs and weigh each glass of water.
9. You can now calculate the density of the water in each glass by using the equation density = mass/volume. Use the weight that you just measured for the mass, and the volume of water that you put in each glass, which was 400mL.
10. Compare the results of your calculations to your guess. Were you correct about which glass had the highest density?
Misc. Helpful Information/ Hints/ Suggestions:
To make the lab more fun for younger age groups, allow them to use food coloring in the water, and to decorate their "swimming" eggs.