“HOW DO I LOVE THEE LET ME COUNT THE WAYS...” DETERMINATION OF AVOGADRO’S CONSTANT
Calibration drop counting
MSDS available for
• • stearic acid, CH3(CH2)16COOH cyclohexane, C6H12
molar volume molecular structures surface areas and volumes Avogadro’s constant percent error
Recommended Advanced Reading
Chapter 3 in Petrucci, Herring, Madura, & Bissonnette’s General Chemistry,10th Ed.
The beginning When you begin this experiment, you should have a lab work area, a TA (or demonstrator) and a partner. In today's session you will work with your partner to: Calibrate a dropper and determine the number of drops of a stearic acid in cyclohexane solution required to create a monolayer of the solution on a water surface Calculate the mass of stearic acid required to form the monolayer, use it to estimate the thickness of the monolayer (which is related to the length of the stearic acid molecule), and then use the number of carbon atoms in stearic acid to approximate the diameter and then the volume of a carbon atom calculate a value for the Avogadro constant compare your calculated value for the Avogadro constant with a known value and determine the percent error in your value
This is a general overview of what you will be accomplishing in this experiment.
Determination of the Avogadro Constant
“In a diamond shaped like a cube of 15 mm per side, there
are between 500 and 1000 times more carbon atoms than there are stars in the entire visible Universe!”
The Avogadro constant is one of the most important constants used in chemistry. It allows chemists to relate a directly measurable quantity, such as the mass of a substance in grams, to a quantity that cannot be measured directly, such as the number of atoms in the mass of a substance. For instance, the Avogadro constant could be