2014.01.29 Postlab Report 1 Colligative Properties And Osmotic Pressure A 6a1n42

Lab 1: Colligative Properties & Osmotic Pressure Purpose / Introduction The purpose of this lab experiment is to observe and compare the freezing points of a pure solvent and a solvent mixed with a nonvolatile solute in a solution. Unlike most properties, the freezing point of a solution depends on the number of solute particles present in the solution. It should be expected that they results of this part of the experiment will show that the freezing point of the pure solvent will be lower than that of the solution. In addition to observing the freezing points, the experiment also allows the viewer to observe and develop and understanding of osmosis: the principle dialysis is based on. Osmosis is the practice of particles moving between different concentrations via a semi-permeable membrane until equilibrium is met. To stop particles from ing through the semi-permeable membrane, a pressure is needed; this pressure is called osmotic pressure. Osmotic pressure is also dependent on the number of solute particles presented. It should be expected that the Karo syrup in the dialysis tubing will travel through the semi-permeable membrane into the distilled water until equilibrium is met. If the pores in the tubing are large enough, the distilled water will do the same, but into the tubing; if the pores are too small to allow the distilled water molecules to through, the dialysis tubing will shrink as the syrup leaves the tubing. Prelab Questions N/A Procedure Refer to CHE 112-BK01 lab manual Lab 1: Colligative Properties & Osmotic Pressure (page 14) Data / Results Part I: Colligative Properties Seco nds 0 30 60 90 120 150 180 210 240 270 300 330 360

Room Temp

℃

19 19 19 19 19

Freezing Point 2

Ice Bath

℃

19 8 6 5 5 4 3 3 2 2 2 2 2

Pure Water 20 15 Temperature (Celsius) 10 5 0 0

100

200

300

Time (seconds) Distilled Water Room Temp

Distilled Water Ice Bath

400

Seco nds 0 30 60 90 120 150 180 210 240 270 300 330 360

Room Temp

℃

Ice Bath

19 19 19 19 19

℃

19 9 5 4 4 3 3 2 2 2 2 2

Salt Solution 20 15 Temperature (Celsius) 10 5 0 0

100

200

300

400

Time (seconds) Saltwater Room Temp

Saltwater Ice Bath

Freezing Point 2 Postlab Questions

B. The freezing point of the pure water was 2 ℃ . The freezing point of the salt water solution was also 2 ℃ . C. The two freezing points are the same; however, from my knowledge of colligative properties, the freezing points should have differed; the pure water freezing point should have been less than the freezing point of the salt water solution. D. There are many practical applications using colligative properties. Anti-freeze is a useful application of freezing point depression and boiling point elevation; anti-freeze keeps the engine from freezing in the winter season, while it also keeps the engine from overheating in the summer time. Part II: Osmotic Pressure Sugar Solution Prior Pure Water

After Pure Water

Dialysis tube full of Karo syrup Water clear, no visible distortion in light

Raw Egg* Prior Vinegar Hard shell Opaque color Textured bumps on shell Elongated on one side, rounded on other side

Dialysis tube expanded

After Vinegar

After Karo Syrup

Shell gone Sunrise orange color Can see yolk Rubber ball-like texture Slightly larger Elongated side rounded out

Egg white shrunk to just yolk Shape is lost Yolk and membrane remain Distortion of light in Karo around egg (water from yolk)

*Lab was repeated using apple cider vinegar instead of white vinegar. After a week, the shell did not appear to have dissolved; however upon further inspection, the shell was dissolved enough to be wiped away from the membrane under cool tap water. Additionally, dark stringy material developed in the apple cider vinegar shortly after the egg was submerged, and after a period the vinegar level began to lower.

Postlab Questions A. A dialysis bag is similar to the kidney. A kidney and a dialysis bag both allow certain cells and molecules to through the membrane while keeping other cells and molecules from ing through the membrane. This is an important process for the kidneys because it filters out waste from the arteries and veins. The difference between the kidneys and a dialysis bag is the material the membranes are composed of. Unlike the kidney, the dialysis bag is incapable of preferential transportation of ions; instead, the size of the dialysis bag's pores prevents molecules and materials too large to fit through the pores, thus keeping such molecules and materials from diffusing into the higher concentration. B. The Karo syrup is hypertonic to the egg because the water moves from inside the egg to the Karo syrup. C. T =23.6 ℃=297.1 K Π=MRT V =0.500 L

1 atm=760 mmHg

m=0.302 g solute

K=

Π=8.34 mmHg

1K ( 1℃ )+ 273.5 K

R=0.0821

(

0.01097 atm=M 0.0821 M=

L ∙ mol ( 297.1 K ) K ∙atm

)

8.34 mmHg ×

L ∙mol K ∙ atm

1 atm =0.01097 atm 760 mmHg

0.01097 atm ∙mol 24.39 atm ∙ L −4

M =4.498 × 10 4.498 ×10−4

mol L

mol ×500 L=2.249 ×10−4 mol L

2.249 ×10−4 mol=0.302 g 0.302 g g =1340 −4 mol 2.249 ×10 mol

The molecular mass of the antibiotic is

1340

g mol .

Conclusion Part I of the lab did not produce the expected results. The freezing point of the pure water should have been lower than the freezing point of the saltwater solution; unfortunately, our *Lab was repeated using apple cider vinegar instead of white vinegar. After a week, the shell did not appear to have dissolved; however upon further inspection, the shell was dissolved enough to be wiped away from the membrane under cool tap water. Additionally, dark stringy material developed in the apple cider vinegar shortly after the egg was submerged, and after a period the vinegar level began to lower.

results yielded the same freezing point. It is possible we did not let the pure water sit in the ice bath long enough to achieve the appropriate temperature that would yield results that agree with the expected and tried-and-true results. On the other hand, part II of the lab did yield expected results. As expected, the distilled water diffused into the dialysis tube where the concentration of the Karo syrup was high in comparison to the outside environment. As a result, the dialysis tube expanded as water traveled across the membrane until equilibrium was met. The results of the raw egg also yielded accurate results; except, in the raw egg's case, the water from inside the egg diffused across the membrane to the highly concentrated Karo syrup outside the egg. This process continued until the equilibrium was met.