Density of Liquids

[Pages:4]Kelsey Strouse Lap Partners: Luis Rulvacaba/ Ellie Puttman 10/2/13

Density of Liquids

ABSTRACT: In this experiment, the density of water and an unknown liquid were calculated by finding the mass and volume in three separate trials for each liquid. Very precise results were found and the average density obtained for the water was 1.0g/mL, and the density for the unknown was 0.83g/mL. The results were not accurate because the accepted value of water is 0.998 g/mL and the accepted value for the unknown is 0.791g/mL. The percent error for the water is 0.20% and the percent error for the unknown is 4.93%.

INTRODUCTION: Density is a ratio and can be calculated by dividing the mass by the volume, density= mass/ volume. The density of the same substances, no matter the size or temperature, will remain constant and have the same density. There are two common measurements of density are g/mL and cm3. In this lab, the density of distilled water will be found in three different trials. An average will be obtained. Three trials will be given again, but for a mystery liquid. The percent error will be calculated for both liquids.

PURPOSE: The purpose of this experiment is to identify an unknown liquid by finding the density of that liquid.

PROCEDURE: Six micropipets were obtained and labeled 1 through 6. The micropipets were then massed to the nearest 0.01g and recorded in Data Table 1. Micropipets #1, #2 and #3 were then filled completely with tap water and massed to the nearest 0.01g and recorded in Data Table 1. The water was then transferred from micropipette #1 to a dry graduated cylinder and the volume was recorded in Data Table 1. This step was repeated for micropipets #2 and #3 and was also recorded in Data Table 1. 50mL of an unknown liquid was then obtained. Micropipets #4, #5 and #6 were then filled completely with the liquid. The same process that was used for the earlier micropipets was used again to find the mass and volume of these micropipets. The data was recorded in Data Table 2. After all liquids were disposed of, the lab area was clean and hands were washed before leaving the laboratory.

RESULTS: The unknown C and the water were both clear. The water had no odor. Unknown C had a strong alcohol based odor. The data was recorded for both samples below.

Data Table 1- Water

Mass of empty micropipet (g) Mass of filled micropipet (g) Mass of water (g)

Volume of water (mL)

Density of water (g/mL)

Trial 1 1.30 10.3 9.00 8.9 1.0

Trial 2 1.30 10.3 9.00 9.0 1.0

Trial 3 1.40 10.3 8.90 8.9 1.0

Kelsey Strouse Lab Partners: Luis Rulvacaba/ Ellie Puttman 10/2/13

Data Table 2- Unknown C

Mass of empty micropipet (g) Mass of filled micropipet (g) Mass of unknown (g)

Volume of unknown (mL)

Density of unknown (g/mL)

Trial 1 1.40 8.40 7.00 8.5 .82

Trial 2 1.30 8.30 7.00 8.7 .85

Trial 3 1.20 8.60 7.40 9.0 .82

Mass Calculations The mass of the water and unknown trials were calculated with the formula: Mass = filled micropipet ? empty micropipet. Example: water trial 1: 10.3g ? 1.30g= 9.00g

Density Calculations The density was calculated for both the water and unknown trials with the formula: density = mass/ volume. Example: water trial 1: 9.00g/ 8.90mL = 1.0g/mL

Data Table 3- Density

Water (g/mL) Unknown C (g/mL)

Trial 1 1.0 N/A

Trial 2 1.0 N/A

Trial 3 1.0 N/A

Trial 4 N/A 0.83

Trial 5 N/A 0.83

Trial 6 N/A 0.83

Average Density Calculations The average density was calculated for the water and unknown trials with the formula: sum of all trials (water and unknown) / 3. Example: unknown trials 1, 2 and 3: (.820+.850+.820) / 3= .830g/mL.

Data Table 4- Average Density Water (g/mL)

Unknown C (g/mL)

Average Density 1.0 0.83

Kelsey Strouse Lab Partners: Luis Rulvacaba/ Ellie Puttman 10/2/13

After calculating the average density for Unknown C, it was determined that Unknown C is Methanol.

Percent Error Calculations The percent error of the water and unknown trials was calculated with this formula: (measured valueaccepted value) / accepted value X 100%. Example: water trials: The accepted value for the density of water 1.0 g/mL, so (1.0 -1.0) / 1.0 X 100% = 0%

Data Table 5- % Error Water (g/mL)

Methanol (g/mL)

Accepted Value 1.0 0.79

Measured Value 1.0 0.83

Percent Error 0

4.9%

CONCLUSION: The purpose of this experiment was to determine what an unknown liquid was by finding its density. There were two liquids used in the experiment. One was water and the other was an unknown liquid. There were three trials for each and the density of each trial was calculated. Then the average density was then calculated. Based on the data of the average density of the unknown (0.830g/mL), the most likely choice for the unknown would be methanol at an accepted density of 0.791g/mL. There was also the possibility that the unknown was not even on the list since there was no liquids with the density in the 0.800g/ml-0.899g/mL category. The unknown was actually methanol with a density of 0.791g/mL. With this knowledge, the results still had high precision but a low accuracy. The measured values differ from the accepted values so much because there may have been left over water in the beaker when the methanol was put into it. Allowing the beaker to have time to dry before adding the methanol would have avoided this problem. The results were not what were expected, since there was a huge percent error. The purpose was not accomplished because of the moderate gap between the accepted and measured values.

DISCUSSION: There were many possible places for error. One would be the uncertainty of the measuring tools that were used. If there was an error from measurement it would have most likely came from the mass measurements, since they had lower precision between the mass and the volume measurements. The volume measurements were not precise because all the measurements came out to slightly different recordings. Another possible error was that the temperature of the liquid, when the density, measured value and accepted value were recorded, was different. This would be a problem because as liquid gets warmer, it becomes less dense and vice versa as the liquid gets cooler. This can be viewed in ice and water. The ice is less dense than the water because it is a solid and has a much lower temperature. Another possible source of error was how closely related the densities were on the listed liquids. For example if the density of 0.79g/mL was recorded, there would be three possible choices to make. There is ethanol at 0.789g/mL, isopropyl alcohol at 0.786g/mL and methanol at 0.791g/mL. Without correctly knowing the right liquid, there is no way to tell which liquid the unknown is. The final possible source of error could have been that the methanol and water were mixed within the micropipet and/or the beaker, and the liquid was no longer pure. Since there was such a moderate margin between the measured and accepted values, one of the possible sources of error must have played a large part on the outcome.

Kelsey Strouse Lab Partners: Luis Rulvacaba/ Ellie Puttman 10/2/13

Density is one of the physical properties used to determine what a substance is, but it is not always accurate. There are many possible sources of error that will affect the outcome. There are several examples of density in everyday life that are very obvious but often looked over. One example is cleaning up a petroleum oil spill in sea water. The oil is on top of the water, so the methods of clean-up have to concentrate precisely on top of the water. Another example is how the ice affects organisms in an environment. The ice is on top of the water and animals like polar bears can't get into the water if the ice is too thick. If the ice is too thin, they can fall in and won't survive because they can't spend the rest of their lives in water.

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