Lab 1: Colligative Properties & Osmotic Pressure

Purpose / IntroductionThe 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 passing 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 pass through, the dialysis tubing will shrink as the syrup leaves the tubing.

Prelab QuestionsN/A

ProcedureRefer to CHE 112-BK01 lab manual

Lab 1: Colligative Properties & Osmotic Pressure (page 14)

Data / ResultsPart I: Colligative Properties

Seconds

Room Temp ℃

Ice Bath ℃

0 50 100 150 200 250 300 350 4000

5

10

15

20

Pure Water

Distilled Water Room Temp Distilled Water Ice Bath

Time (seconds)

Tem

pera

ture

(Cel

sius)

0 19 1930 19 860 19 690 19 5

120 19 5150 4180 3210 3240 2270 2300 2330 2360 2

Freezing Point 2

Seconds

Room Temp ℃

Ice Bath ℃

0 50 100 150 200 250 300 350 4000

5

10

15

20

Salt Solution

Saltwater Room Temp Saltwater Ice Bath

Time (seconds)

Tem

pera

ture

(Cel

sius)

0 19 1930 19 960 19 590 19 4

120 19 4150 3180 3210 2240 2270 2300 2330 2360

Freezing Point 2

Postlab QuestionsB. 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 PressureSugar SolutionPrior Pure Water After Pure WaterDialysis tube full of Karo syrupWater clear, no visible distortion in light

Dialysis tube expanded

Raw Egg*Prior Vinegar After Vinegar After Karo SyrupHard shellOpaque colorTextured bumps on shellElongated on one side, rounded on other side

Shell goneSunrise orange colorCan see yolkRubber ball-like textureSlightly largerElongated side rounded out

Egg white shrunk to just yolkShape is lostYolk and membrane remainDistortion 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 QuestionsA. A dialysis bag is similar to the kidney. A kidney and a dialysis bag both allow certain cells and molecules to pass through the membrane while keeping other cells and molecules from passing 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 V=0.500L m=0.302 g solute Π=8.34 mmHg

Π=MRT1 atm=760mmHg

K=( 1 K1℃ )+273.5 K

R=0.0821L ∙ molK ∙ atm

0.01097 atm=M (0.0821L∙ molK ∙ atm ) (297.1 K )

M=0.01097 atm ∙ mol24.39 atm∙ L

M=4.498 ×10−4 molL

4.498 × 10−4 molL

×500 L=2.249 ×10−4 mol

2.249 ×10−4 mol=0.302 g 0.302 g

2.249× 10−4mol=1340

gmol

8.34 mmHg×1 atm

760 mmHg=0.01097 atm

The molecular mass of the antibiotic is 1340g

mol.

ConclusionPart 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 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.

*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.