Density/Buoyancy Lab Report

Samantha Karp
9/24/08
Density and Buoyancy Lab
Introduction:
When first presented with the experiment, I was excited to begin, as I was wondering what the outcome would be. This experiment, which tested density, was conducted over the course of several days. The assignment was to discover the necessary density of the vial in order for it to stay in the middle of the two types of water. The water had different temperatures, as one was frigid salt water, and one was warm tap water. The warm tap water was dyed blue with food coloring, as to see the separation between the water more clearly. The warm tap water was on top of the salt water, as it had a lower density. We were told that the salt water had a density that was greater than one, and the tap water had a density of less than one, but we were not given the exact densities. In order to perform this experiment, we had to use the density formula. The density formula is mass per unit volume, represented by D=m/V, with D being density, m being mass, and V being volume. We hypothesized that the density had to be one, so it could remain in the middle. This experiment was very interesting and exciting to perform.

Hypothesis:
We hypothesized that the vial needed to have a density of around one, as the two types of water had densities greater than one and less than one. Furthermore, we knew that we had to fill the vial with either salt or sand, in order to have the vial remain in the middle. We made this hypothesis using the density formula and the variables that were given.

Materials:
• 1 graduated cylinder
• 1 fish tank
• 1 balance
• 2 vials
• Warm tap water
• Cold salt water
• Blue food coloring
• Sand
• Table Salt
• Pencil
• Paper
• Calculator

Methods
1. Gather all the materials
2. Get the salt water and measure out the desired amount
3. Get the warm tap water and measure out the desired amount
4. Using the blue food coloring, dye the warm tap water blue
5. Put both the salt water and the tap water into the fish tank, they should separate into two layers, with the salt water being on the bottom.
6. Fill the graduated cylinder with water. Do not fill it all the way up, but simply fill it up to about halfway. We filled it up to 52.3 mL.
7. Record the amount of water that was put in the graduated cylinder
8. Get the vial and put some sand in it. You may measure and record the amount of sand that is put into the vial, if desired. A good amount is around 13.0 mL of sand.
9. Place the vial with the sand into the graduated cylinder.
10. Record how much the water rises.
11. Subtract the value from step ten from the initial value of water that was put into the graduated cylinder. Record the results. This is the volume of the vial.
12. Measure and place some sand into the vial. Record how much sand was put into the vial.
13. Measure the mass of the sand and the vial using the balance. Record the results.
14. Divide the calculation from step 13 by the volume of the vial, which is step 11. This will give you the density.
15. If the density is very close to or at one, place the vial into the fish tank. Record the results.
16. If the vial was resting in the middle of the fish tank, record the data and share your results.
17. If the vial sunk or float, repeat steps 12-16, until the vial is resting in the middle.
18. Record and analyze all of the data.

Data/Results
Volume of the Vial: 52.3 mL=initial amount of water in the graduated cylinder
76.8 mL=terminal amount of water in the graduated cylinder
76.8mL-52.3mL=24.5ml=Volume of the vial
Density
Amount of Sand (mL) 13.0 11.9 12.7 12.25 12.5 12.6 12.8
Mass (g) 26.4 24.49 24.6 24.55 25.62 24.77 24.8894
Density (g/cm3) 1.077 .999 1.004 1.002 1.046 1.011 1.0158

The last number in the table, with a mass of 24.8894, was the vial that stayed in the middle. We used 12.8 mL of sand, which gave us a density of 1.0158. This was the second closest that we came to getting a density of 1, which was our goal. Even though we had a density that was 1.011, which was the closest to one, that vial still rose to the top of the water. However, even though it wasn’t exactly one, the final vial was still resting in the middle of the two types of water.

Discussion/Analysis
Our hypothesis, which was that we needed to get a density close to or around one, was proven correct. Although the vial that worked was not the closest to one, as there was another number that was closer to one, it still proves our hypothesis. Although we had to try numerous times, we were always very close to our goal density of one. The farthest density from one that we got was 1.077, which was the first value that we tested. Additionally, none of our vials sank. The vials that did not work were always too light, and we needed to add more sand, since the vials were floating to the top. We were hesitant to add a lot more sand to the vial, as we preferred that it did not sink. This would explain why all of our measurements are very close together, because the amount of sand that we added was very small. Although I am very pleased with how the experiment turned out, there would be some improvements that I would make. First, I would have recorded my notes on a neater sheet of paper, in a neater fashion. However, my results are still shown, but I would prefer a neater sheet next time. Furthermore, I would measure the amounts more carefully. Because science is an exact subject, all the measurements need to be precise, as a tenth of a decimal can make a difference. Finally, I would be more hesitant to put the first vial in the fish tank, and make sure that all the measurements were exactly how I wanted them. Although I would make these changes, I am very pleased with the way we executed the experiment.

Conclusion
This experiment was both interesting and challenging for me. It was interesting because I was excited to know what the answer to the experiment was, and I could not wait to get the result. However, determining the exact amount of sand to put in was challenging. This experiment made us think critically about what we needed to do, and how we could use the variables that were given, along with our prior knowledge. Once we knew how to perform the experiment, it was much less challenging. I enjoyed performing this experiment very much.