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Chem 105 Avogadro's Number Lab
Lab
Course
General College Chemistry (CHEM 105)
365 Documents
Students shared 365 documents in this course
University
Brigham Young University
Academic year: 2023/2024
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Avogadro’s Number
OBJECTIVE: To estimate the value of Avogadro's Number from a monolayer of oleic acid molecules on
water.
INTRODUCTION
Atoms and molecules are too small to count one by one. Avogadro’s Number, or a Mole, was defined to
make these calculations and measurements easy. Just as the word “dozen” means the number 12 no
matter what the objects are, the word “mole” means the number 6 x 10 23 no matter the identity of
the object.
In this experiment, you will estimate the value of Avogadro’s number by determining the area of a
known mass of oleic acid that floats on the surface of water. A key factor in this experiment is the fact
the oleic acid molecules spread out as individual, separate molecules, forming what is referred to as a
monolayer. An estimated value of Avogadro’s number can be calculated using the number of moles of
oleic acid in the monolayer, the known density of oleic acid, the measured surface area of the
monolayer, and simple geometry.
Station 1
Procedure
1. Fill Plastic Dish all the way with water to the top until the dish is full.
2. Using a syringe, measure out 1 ml of oleic acid to form one single monolayer or bubble on top
of the water in the center of the plastic dish. If the oleic acid bubble splits into multiple bubbles,
use the tip of syringe to join them together. Make sure the bubble does not touch the sides of
the dish. This lens is a monolayer of oleic acid molecules.
3. Measure oleic lens radius with the ruler in order to calculate the area of the oleic acid lens
later. Area= πr 2
4. When done with calculations, dispose of the water and oleic acid mixture in the Unwanted Lab
Materials.
Calculations:
Use the table below to put your final answers for the calculations. In order to estimate
Avogadro’s number, we need to know the number of molecules in the Oleic acid monolayer and
how many moles of oleic acid we used. Molecules/moles will get you Avogadro’s number.
To calculate molecules of oleic acid
1. Calculate area of oleic acid lens in water using Area= πr 2 using radius
2. Given the area of 1 molecule of oleic acid (0 2 ) find the number of molecules in oleic
acid lens.
(Area of monolayer/area of 1 molecule) = number of molecules
3. Record number of oleic acid molecules in the table.
To calculate moles of oleic acid
1. convert ml of oleic acid to moles
***remember that Oleic acid has a molar mass of 282 g/mol and that Oleic acid density is on the
bottles. Density= .01mg/1mL
To calculate estimated Avogadro’s number, divide molecules of Oleic Acid/Moles of Oleic acid.
Radius of
monolayer (in
cm)
Area of
monolayer (in
cm2)
# Molecules of
Oleic Acid
# moles of Oleic
Acid
Avogadro’s
number estimate
d. The moon: 2 x 10 19 m 3
6. Why is it usually more useful to describe a material in grams/mole rather than amu?
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Chem 105 Avogadro's Number Lab
Course: General College Chemistry (CHEM 105)
365 Documents
Students shared 365 documents in this course
University: Brigham Young University
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Avogadro’s Number
OBJECTIVE: To estimate the value of Avogadro's Number from a monolayer of oleic acid molecules on
water.
INTRODUCTION
Atoms and molecules are too small to count one by one. Avogadro’s Number, or a Mole, was defined to
make these calculations and measurements easy. Just as the word “dozen” means the number 12 no
matter what the objects are, the word “mole” means the number 6.02 x 1023 no matter the identity of
the object.
In this experiment, you will estimate the value of Avogadro’s number by determining the area of a
known mass of oleic acid that floats on the surface of water. A key factor in this experiment is the fact
the oleic acid molecules spread out as individual, separate molecules, forming what is referred to as a
monolayer. An estimated value of Avogadro’s number can be calculated using the number of moles of
oleic acid in the monolayer, the known density of oleic acid, the measured surface area of the
monolayer, and simple geometry.
Station 1
Procedure
1. Fill Plastic Dish all the way with water to the top until the dish is full.
2. Using a syringe, measure out 1ml of oleic acid to form one single monolayer or bubble on top
of the water in the center of the plastic dish. If the oleic acid bubble splits into multiple bubbles,
use the tip of syringe to join them together. Make sure the bubble does not touch the sides of
the dish. This lens is a monolayer of oleic acid molecules.
3. Measure oleic lens radius with the ruler in order to calculate the area of the oleic acid lens
later. Area= πr2
4. When done with calculations, dispose of the water and oleic acid mixture in the Unwanted Lab
Materials.
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