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Avogadro’s Number Oleic Acid Pancake Experiment 6.022 ×1 023 Calculations 1. Calculate Average Diameter: d 1+ d 2 + d 3 Average Diameter= 3 13.0 cm+10.5 cm +11.0 cm Average Diameter= 3 Average Diameter=11.5 cm 2. Calculate Radius: Davg R= 2 11.5 cm 2 2 R=5.75 cm R=

3. Calculate Area of Film A=π r 2 2 5.75 cm¿ A=π ¿ 2 A=103.87 cm 4. Calculate the Volume of a Single Drop 1.0 cm3 V= 24 V =0.042 cm3 5. Calculate the Volume of Oleic Acid 5 V =volume of a single drop × 1000 5 3 V =0.042 cm × 1000 −4 3 V =2.1 ×1 0 c m Calculate the Depth of the Layer volume of oleic acid Depth= areaof film 0.000 21 cm3 Depth= 103.87 c m2 −6 Depth=2.02 ×1 0 cm Assume Oleic Acid molecules are perfect spheres, depth = diameter

Calculate the Diameter of Molecules Volume of Oleic Acid Diameter of Molecules =Depth= Area of Film 3 0.0021 c m −6 Diameter of Molecules =2.02× 10 cm=¿ 2 103.87 c m −6 −6 Diameter of Molecules =2.02× 10 cm=2.02 ×1 0 cm

6. Calculate Avogadro’s Number a) Formula of Oleic Acid C H 2 ¿7 COOH C H 2 ¿7 CH =CH ¿ Oleic Acid: C H3 ¿ b) Density H2O: 1.0g/mL Oleic Acid: 0.874g/mL c) Volume of Oleic Acid V OA=2.1×1 0−4 c m3 Molecular Weight of Oleic Acid The chemical formula for oleic acid is C17 H 33 COOH ; giving a molecular weight of about 282. 282gm of Oleic Acid has Avogadro’s number worth of molecules in it. 1. Find number of moles of Oleic Acid −4 Volume Oleic Acid =2.1× 10 mL 0.895 g =1.9× 10 14 g PureOleic Acid mL mol 14 =6.7 × 1 011 mol Moles of Oleic Acid =Mol A=1.9 × 10 g Pure Oleic Acid × 282 g 2. Find number of molecules of Oleic Acid Area of Oleic Acid Film: 5.75 cm2 Thickness of Oleic Acid Film: 2.02 × 10−5 cm Thickness of Monolayer (Area x Thickness) of the molecule: 1.2 × 10−4 Assuming a molecule of Oleic Acid is a cube, solve for the volume of the molecule. 3 V Molecule =Thickness 1.2 ×1 0−4 ¿3 V Molecule=¿ V Molecule =1.6 ×1 0−12 1Molecule =V Molecule 1Molecule =1.6 × 1 0−12 MassOleic Acid=2.1 ×1 0−4 mL ×

Number of Molecules=V A ×

1Molecule V Molecule 14

Number of Molecules=1.9× 1 0 g Pure Oleic Acid × 26

Number of Molecules=1.2× 10 molecules 3. Calculate Avogadro’s Number Number of Molecules Avogadr o ' s Number= Mo l A

1 Molecule (1.56 ×1 0

−12

)

1.2× 10 26 molecules 6.7 × 1 011 mol ' Avagadr o s Number=1. 8 ×1 014 Avagadr o ' s Number=

Summing Up 1. What is meant by a monolayer? A layer that is one molecule thick. 2. Why is it necessary to dilute the Oleic Acid for this experiment? Why Alcohol? If we were to use pure Oleic Acid, the film will be larger than the pan. Alcohol is ideal for diluting Oleic Acid, as it mixes with it, and quickly evaporates once the drop hits the water, so it won’t add to the size of the slick. 3. The shape of oleic acid molecules is more like that of a hot dog than a sphere. Furthermore, one end is attracted to water (hydrophilic) so that the molecule stands up on the surface of the water. Assume an oleic molecule is 10 times longer than it is wide. Then estimate the volume of one oleic acid molecule. Oleic Acid has one hydrophobic and one hydrophilic end. When a small amount of oleic acid is placed on the surface of water, it stands on end with the hydrophilic end towards the water and the hydrophobic end away from the water. To solve this problem, I’ll use the diameter of the monolayer Oleic Acid created in our experiment, the radius, height, the equation for the volume of a cylinder, plus the volume of the sphere (previously calculated single drop). Diameter (Width) = 2.02 × 10−6 cm Radius= 1/10th Diameter = ( 2.02 × 10−7 ¿ cm2 Height=1/20th Diameter = 1.01 × 10−7 cm V olume of Cylinder=hπ r 2 −8

2

2.02× 1 0 ¿ cm −8 V =1.01 ×1 0 × π ׿ V =6.40947733 ×1 0

−16

Estimate Volume of 1 Oleic Acid Molecule (10 times longer than wide) =

−16

6.40947733× 1 0

Class Questions 1. Will Oleic Acid dissolve in Water? No, Oleic Acid will not dissolve in Water. 2. Why won’t Oleic Acid dissolve in Water? In this experiment, Oleic acid is the solute, and Water is the solvent. Mixing these two molecules leads to solute-solvent interactions. Oleic Acid will not dissolve in Water, but does dissolve in Alcohol, however, forming a monolayer on top of the Water. Oleic Acid is an organic, nonpolar, compound. Since it’s nonpolar, its Intermolecular Force is Dispersion Force. In this experiment, we add Oleic Acid to Water, which is a polar molecule. Since Water is polar, its Intermolecular Forces are Hydrogen Bonding and Dispersion Forces. The Oleic Acid molecule has a hydrophobic end and hydrophilic end. The hydrophobic end is structured like a hydrocarbon, while the hydrophilic end is structured like a carboxylic acid. Hydrogen Bonds occur between the carboxylic end of the Oleic Acid molecules and the water in the tray. While Van der Wall forces describe the interactions between the hydrophobic ends of the Oleic Acid molecules as the Oleic Acid molecules align themselves vertically on the surface of water. In summary, most of the Oleic Acid molecule is nonpolar with a small part being polar. The nonpolar sections win and determine its solubility in water. From this experiment, it can be stated that molecules dissolve in polar liquids if the solute is predominantly polar, or in nonpolar solvents if the solute is predominantly nonpolar....