In this experiment we will determine Avogadro’s number by calculating the area of a one-molecule thick layer of oleic acid. Because we know the volume of one molecule, we can solve for area. Then, we use density and the molar mass of oleic acid to find Avogadro’s number.
The purpose of this lab was to give us a different perspective of where Avogadro’s number comes from. We learn in a hands-on approach how it can be determined by the unique properties of oleic acid, water, and pentane.
The first step in this lab was to achieve a properly diluted solution of oleic acid. This turned out to be the key step in returning accurate results. We did this using the not-so-precise method of measuring 1mL of the original solution of 1 part oleic acid and 10 parts pentane, and moving it into another test tube of 10mL pentane. This was repeated two more times.
The next step was preparing a surface to allow the oleic acid to spread out so that it was only one-molecule tall. This involved using a large convex watch-glass, pouring water onto the top until there was enough surface tension to create a near-perfectly-flat surface. 0.05mL of the dilute solution was then dropped onto this surface. Because pentane is so volatile, it evaporated quickly leaving only the oleic acid. We were able to see this because of the light dusting of Lycopodium powder which was forced out of the way of the oleic acid.
IntroductionChromatography is a common technique used by biochemists in separating and identifying different amino acids and helps to reveal the function of cell organelles. Chromatography is particularly approved for its accuracy in distinguishing between each compound, which it does by separating the chemicals according to their Relative Molecular Mass (RMM). The term was introduced in 1906 by ...
Using the rough technique of sketching the outline of the oleic acid onto a plate of glass we were able to determine the area. By setting a simple proportion to find the weight to area ratio for printer paper, we solved for the approximate area of the oleic acid.
Using a formula provided, we calculated the true volume of the oleic acid in cubic centimeters or milliliters. The next step was to finally solve for the number of molecules. We know that by multiplying molar mass times the inverse density times the inverse volume, we can find molecules (g/mol x mL/g x mL/molecule).
Our first trial proved to be the most accurate: we determined there were 4.9 x 1023 molecules of oleic acid, an error of approximately -1.1 x 1023.
There are two major sources of error in this experiment. The first is in the creation of the diluted solution. Measuring 1mL accurately with a syringe can be difficult, I think that we should have used our 5mL pipettes which are very accurate. The second source, is in determining the area of the oleic acid. The outline formed on the water is not very crisp, and therefore cannot be sketched accurately.
1.Both the water and the ending COOH group at the end of oleic acid are polar. This creates dipole-dipole attraction between the two, which is fairly strong. Within the non-polar carbon-atom chain there is LDF forces, which in a large number can be strong. The dominant force is the dipole-dipole between COOH and H2O which is the reason why the oleic acid chains stand on end next to water along with the fact that the non-polar carbon chain repels water..
2.Through LDF forces.
3.H = 1.008g -> H2 = 2.016g
O = 16.00g
H2O = 18.02g
1g/mL x 1000mL/1L = 1000g/L
1000 / 18.02 = 55 moles
55 moles x (6.02 x 1023) molecules/mol = 3.3 x 1025 molecules
2 bonds/molecule x (3.3 x 1025) molecules/1L = 6.6 x 1025 bonds