Experiment #1 - Post Lab for Densities of Solids and Liquids lab. PDF

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Post Lab for Densities of Solids and Liquids lab....

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Densities of Solids and Liquids: Mass/ Volume Measurements

Objective Statement and Introduction: The most common measurements in a laboratory are mass and volume. In this lab, we utilized basic principles of measuring mass and volume to find the density of an object, while reporting data with correct significant figures to evaluate the precision and accuracy of a volumetric pipet, graduated cylinder, and beaker. The purpose was to gain experience with common lab practices along with lab equipment. Measuring accurately and precisely is essential in carrying out any scientific research or theory development. However, measurements are only as accurate as the limitations of the measuring tool allow, which is why it is important to calculate with the correct number of significant figures. Two properties we calculated frequently in this lab were the density and volume. Density is found by dividing the mass (grams) by volume (mL), p=m/v. This equation can be manipulated in a few ways to solve for one of the three variables.

Procedure and experimental details: There are 4 parts to the lab. For this experiment, we will be running three trials for each. For part A, we calibrated the volumetric pipet to determine accuracy and precision. We weighed a dry, empty 50 mL beaker. We then took the temperature of the water that we were using to see what the density was. At 21.0 degrees celsius, the density of our water was .997992 g/ml. The 10 mL volumetric pipet was used to add 10mL of water to the beaker and we weighed it again. Then, using the given density and the calculated mass of displaced water, we were able to calculate the volume of the water given by the volumetric pipet. We essentially did the same procedure again, except we used a graduated cylinder for the second time. We

also took the temperature of our water again. The water changed from a density of 0.997992g/mL to 0.998099g/mL. For part B, we used the calibrated volumetric pipet to transfer an unknown liquid to a dry beaker that we weighed beforehand. We determined the mass of the liquid by subtracting the weight of the liquid and beaker from the beaker itself. We then used the average volume from the calibration of the pipet to calculate the density of the unknown liquid. For part C, we measured the dimensions of a brass cylinder. Using a ruler, we measured the diameter and height and used those values to determine the volume and density. For part D, we calculated the density of the brass using the dunking method. We started off by measuring the mass of the brass cylinder and the volume of water in the cylinder. We then carefully placed the object into the water and recorded the new volume, calculating the difference in volume, and using that number and the mass to calculate the density of the object. Trial 1

Trial 2

Trial 3

Mass of empty 50 mL beaker

27.32 g

27.35g

27.36g

Mass of beaker + 1 pipet of H20

37.29g

37.31g

37.33g

Mass of H20 transferred

9.97g

9.96g

9.97g

Calculated volume of water

9.99mL

9.98mL

9.99mL

Trial 1

Trial 2

Trial 3

Mass of empty 50 mL beaker

27.3g

27.3g

27.3g

Mass of beaker + 1 graduated cylinder of H20

36.9g

36.9g

36.8g

Mass of water transferred

9.6g

9.6g

9.5g

Calculated volume of water

9.6mL

9.7mL

9.5mL

Trial 1

Trial 2

Trial 3

Mass of empty 50 mL beaker

27.33g

27.35g

27.35g

Mass of beaker + 1 pipet of unknown liquid

38.94g

39.02g

38.98g

Mass of unknown liquid

11.61g

11.67g

11.63g

Calculated density of unknown liquid

1.16g/mL

1.17g/mL

1.16g/mL

Trial 1

Trial 2

Trial 3

Mass of brass cylinder

53.90g

53.85g

53.80

Diameter of brass cylinder

1.20cm

1.20cm

1.20cm

Height of object

5.10cm

5.10cm

5.10cm

Volume of object

5.77cm^3

5.77cm^3

5.77cm^3

Density of object

9.34g/cm^3

9.34g/cm^3

9.34g/cm^3

Trial 1

Trial 2

Trial 3

Mass of brass cylinder

53.90g

53.84g

53.80g

Volume of H20 in cylinder

14.5mL

14.0mL

17.0mL

Volume of H20 + object

21.0mL

21.0mL

23.5mL

Calculated volume of object

6.50cm^3

7.0cm^3

6.50cm^3

Calculated density

8.30g/cm^3

7.7g/cm^3

8.2g/cm^3

Calculations: For part A and B Mass of H20/liquid transferred (trials 1-3)= mass #2- original mass

Part A Calculations Calculating volume for pipet (trial 1 and 3) (trial 2, pipet)

9.97/0.997992= 9.99mL 9.96/0.997992= 9.98mL

Average volume for pipet

(9.99+9.98+9.99) = 9.99mL 3 Percent error for calibration of pipette (9.99-10.0) x 100 = -.10% 10.0 Standard deviation ((9.99-9.99)^2+(9.98-9.99)^2+(9.99-9.99)^2)^.5= 0.007mL (3-1) Calculating volume for graduated cylinder (trial 1 and 2) 9.6/0.998099= 9.6mL (trial 2) 9.5/0.998099= 9.5mL Average volume for graduated cylinder (9.6+9.7+9.5) = 9.6 mL 3 Percent error for calibration of graduated cylinder (9.6-10.0) x 100 = -4.0% 10.0 Standard deviation ((9.6-9.6)^2+(9.7-9.6)^2+(9.5-9.6)^2))^.5 = 0.10mL (3-1) Part B Calculations Density of unknown liquid (trial 1) 11.61/9.99 = 1.16g/mL (trial 2) 11.67/9.99 = 1.17g/mL (trial 3) 11.63/9.99 = 1.16g/mL Average density (1.16+1.17+1.16) = 1.16g/mL 3 Part C Calculations Volume of brass cylinder (trial 1,2, and 3) Density of brass cylinder (trial 1,2 and 3)

Average density of brass cylinder % error Standard deviation

(π)(.60)^2 = 5.77 cm^3 53.90/5.77=9.34g/cm^3 53.85/5.77=9.33g/cm^3 53.80/5.77=9.32g/cm^3 (9.34+9.33+9.32)/3 = 9.33g/cm^3 (9.33-8.73) x 100 = 6.87% 8.73 ((9.34-9.33)^2+(9.33-9.33)^2+(9.32-9.33)^2))^.5 =.01cm^3 (3-1)

Part D Calculations Calculated volume of brass cylinder using water displacement

Calculated density

(trial 1) 21.0-14.5 =6.50cm^3 (trial 2) 21.0-14.0=7.0cm^3 (trial 3) 23.5-17.0=6.50cm^3 (trial 1) 53.90/6.50 = 8.30 g/cm^3 (trial 2) 53.84/7.0 = 7.70 g/cm^3

(trial 3) 53.80/6.50 = 8.28 g/cm^3 Average density % error Standard deviation

(8.30+7.70+8.28)/3 = 8.09 ((8.09-8.73)/8.73) x 100= -7.33% ((8.30-8.09)^2+(7.70-8.09)^2+(8.28-8.09)^2))^.5 = .34 g/cm^3 (3-1)

Sources of error/results: There are many possibilities in terms of experimental error, most of which come from human error. When using a volumetric pipet, it is created in a way that purposely retains water in the tip. However, there is almost always a drop of water that you have to let drip out. It is possible that we could have forgotten to do so. We also could have read the ruler inaccurately and rounded to the wrong number. Other possibilities are fluctuating temperatures in water that would, therefore, change the density or scale error in which air movement affects the mass. The results on precision and accuracy are further discussed in the post-lab questions.

Post-lab Questions: 1. Based on our observations, the volumetric pipet is more accurate because it had a lower percent error and a lower standard deviation meaning the measurements were closer to the actual measurement of 10 mL. 2. The volumetric pipet was also more precise because the standard deviation was significantly lower than the one of the graduated cylinder. 3. No, because precision is measured by the number of times you get a similar result. So a single measurement would not allow evaluating for precision. 4. If the water changed temperatures, the density would change, therefore, making the calculations inaccurate and imprecise....