Density and Compsition PDF

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Density and Composition of Solutions 05/10/2021 CHEM-1100 Section 13 Professor Kubo-Anderson Sally Bledsoe

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Purpose: The goal for this lab was to determine the density of various sucrose solutions and to find the fastest and easiest way for finding the corresponding compositions using the direct and indirect methods.

Theory/Principles: When finding the density of these sucrose solutions, you can use the indirect and direct methods. When using the direct method, you use data that you can see. By using the equation 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = [𝑚𝑎𝑠𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟 𝑎𝑛𝑑 𝑙𝑖𝑞𝑢𝑖𝑑−𝑚𝑎𝑠𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑒𝑚𝑝𝑡𝑦 𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟] 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑙𝑖𝑞𝑢𝑖𝑑

, you can use the direct method. This one

may be easier if you know the exact measurements because you have all the numbers right there.The indirect method definitely takes up more time though. This method involves getting a sinker involved. The indirect method to find density is found by the equation below: 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =

[𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑 𝑖𝑛 𝑎𝑖𝑟−𝑎𝑝𝑝𝑎𝑟𝑒𝑛𝑡 𝑚𝑎𝑠𝑠 𝑠𝑜𝑙𝑖𝑑 𝑖𝑛 𝑙𝑖𝑞𝑢𝑖𝑑]1.00𝑔 𝑚𝐿

𝑀𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑 𝑖𝑛 𝑎𝑖𝑟−𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑 𝑖𝑛 𝑤𝑎𝑡𝑒𝑟

. We also must find the percentage by

weight of sucrose by this equation: % 𝑏𝑦 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑢𝑐𝑟𝑜𝑠𝑒 =

100∗𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑢𝑐𝑟𝑜𝑠𝑒 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑢𝑐𝑟𝑜𝑠𝑒+𝑚𝑎𝑠𝑠 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟

.

Using both the indirect and direct methods, we should be able to calculate the composition and density of the unknown sample.

Procedure: There are four parts to this lab. Part A We will need to prepare our sucrose solutions in this section of the lab. Solution A will contain 7.5 grams of sugar and 40 mL of water. Solution B will have 14 g of sugar and 36 mL of

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water. Lastly, Solution C will have 30 g of sugar and 30 mL of water. Make sure the sugar is dissolved all the way in each of the solutions. Part B In this portion, we will be weighing a graduated cylinder with and without liquids. First, find the weight of the empty graduated cylinder. Next, we will measure the cylinder with water in it. After that, we will measure the weight respectively with solutions A, B, and C. Between each one, remember to rinse the graduated cylinder with 2 mL of the solution you will be measuring. Part C In this part, we will need to record the mass of a sinker in different environments. First, we weigh it suspended from a triple beam balance with a string. Next, we will measure the sinker in a 100 mL beaker filled with water. Lastly, we will submerge the sinker in solutions A, B, and C respectively, making sure to completely dry both the beaker and the sinker before measuring for each solution. For each measurement, make sure the sinker does not touch the bottom or sides of the beaker for a more accurate measurement. Part D For the last portion of this lab, we will be testing the unknown. Solution. We will be repeating the processes from part B and C for the unknown solution. Once we find the unknown solutions volume and the sinkers apparent mass in this solution, we can now graph it on excel. The x-axis will be the percent wright of sucrose and the y-axis will be the density. We will include points from both the direct and indirect methods to get a curve.

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Data Tables and Graphs: Part A mL of

Grams of

Solution

Mass of

Mass of

Mass of

water

sucrose

Designation

Empty

beaker +

beaker +

Beaker, g

sucrose, g

sucrose + H2O, g

40.0

7.5

A

61.22

68.74

108.08

36.0

14.0

B

59.92

73.93

109.42

30.0

30.0

C

47.42

71.44

107.20

Part C & D Mass of Sinker, g In air

10.73

In water

9.25

In solution A

9.19

In solution B

9.12

In solution C

8.92

In unknown solution

9.255

Part B & D Mass of empty 10 mL graduated cylinder, g

25.21

Mass of grad. cyl. + 10mL water, g

35.37

Mass of grad. cyl. + 10mL solution A, g

35.97

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Mass of grad. cyl. + 10mL solution B, g

36.62

Mass of grad. cyl. + 10mL solution C, g

37.78

Mass of grad. cyl. + 10mL unknown solution,

36.25

g

Results/Calculations: Part A:

Part B

Part C

Part D

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Direct Method 1.28 1.26 1.24 1.22 1.2 1.18 1.16 1.14 1.12

1.1 1.08 1.06 0

10

20

30

40

50

60

40

50

60

Indirect method 1.24 1.22 1.2 1.18 1.16 1.14 1.12 1.1

1.08 1.06 1.04 1.02 0

10

20

30

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Discussion: Ultimately, the measurements we did in parts B and C lead to the way we calculated part D for the unknown solution. The graphs show us what percentage the unknown is at for the weight of sucrose. The first method gives us about a 21/22 percent for the weight of sucrose. The second results of the indirect method I found to be inconclusive, as the graph doesn’t go smaller than 1.02 on the y-axis. Using the equations specified in the procedure, we were able to calculate the density and composition of each solution, including the unknown. 1. a. Calculate the % uncertainty in each of the measurements you made in parts B and C i. Don’t have actual number to calculate uncertainty b. Calculate the % uncertainty in the densities found in parts B and C i. Don’t have actual number to calculate uncertainty c. Which of the two methods of determining density is the more precise? Give your reasons. i. I believe the first method is more accurate because the measurements only involve the solutions and the graduated cylinder rather than a sinker also mixed in. 2. Calculate the density of the sinker you used a. Density = mass/volume b. Density=10.73/1.48=7.25g/mL 3. The buoyancy method can be used to determine the densities of high melting or corrosive liquids. A platinum sinker suspended by a thin platinum wire from a balance weighted

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58.35 g in the air. When it was completely immersed in the water at room temperature, the apparent weight of the sinker was 49.26g. the sinker was dried and immersed in a crucible containing molten potassium tungstate at 925°C. its new apparent weight was 30.17 g. Use the data given to determine the density of molten potassium tungstate at 925° C. a.

(58.35 − 30.17)/(58.35-49.26)=3.10g/mL

Conclusion: The use of the direct method was the easiest version to use to find the density of each sucrose solution. I found that the indirect method can be a little hard to work with and officially find the percent weight of sucrose of the unknown solution. However, for the known A, B, and C solutions, both the indirect and direct methods worked well. References: Goldwhite, H., Kubo-Anderson, V., Tikkanen, W., Experiemnt 1. Density and Composition of Solution, Experiments in General Chemistry, 5th ed.; The McGraw Hill Compnaies. (2124)...