We’ll be using a simulated experiment involving stearic acid, a structure with a polar and nonpolar end, to estimate Avogadro’s Number.

To access the online lab please navigate to Avogadro’s Number Online Lab. You’ll be completing using this worksheet to collect key information, complete your calculations and reflect upon your experimental findings. You’ll be submitting this worksheet to receive credit for the lab.

Overview

Read through the overview page to understand the different sections of the virtual lab experiment page

Introduction

Read through the introduction page to answer the following questions:

1. What is the most reliable method for determining Avogadro’s number?

2. How did Albert Einstein estimate the number of particles in a mole – before X-ray Crystallography was understood?

3. What was Robert Millikan’s contribution which resulted in the current 6.02 x 1023 particles per mole value we’re familiar with and use today?

4. Copy and paste a picture of the steric acid Lewis structure. Place a box around the end of the molecule that will hydrogen bond with water.

5. If steric acid is placed on water in a one molecule thick film, describe, in your own words, how the steric acid molecules will arrange themselves.

6. What solution will you be using to deliver steric acid to the water surface?

Experiment

The Start Here page has a high-level overview of the experimental steps and equipment. The Procedure Page has detailed information and self-check questions on the overall experimental procedure.

1. Read through the Start Here and Procedure pages to write a detailed procedure you could follow in the lab, in your own words.

Tutorial

Work through the tutorial pages and record the data you collect or calculate for each step, in the table below. You can verify you have the correct calculated value by clicking “Check” and can receive hints to help with you calculation by clicking the lightbulb.

Note on checking your calculations: For small numbers scientific notation is required, but a special form. If you got back 0.00092 as an answer and wanted to check that this was correct you’d need to input 9.2E-4 (representing 9.2 x 10^-4) before clicking “Check”

Initial Calculations

Show your calculations for each of the following, then record your final values in table 1:

1. The volume of the monolayer in mL and conversion of the volume from mL to cm3

2. The area of the water surface (with units)

3. Converting the steric acid solution strength from g/L to g/mL

4. Mass of steric acid in grams

5. Volume steric acid added in cm^3

6. Thickness of the steric acid monolayer in cm

Table 1: Initial Calculations Data Table

Monolayer Volume (mL)

Monolayer Volume (cm^3)

Diameter of water surface (cm)

Area of water surface

Mass of steric acid (g)

Volume steric acid (cm^3)

Thickness of the steric acid monolayer (cm)

Continued Calculations

1. What are the key assumptions being made in our continued calculations?

2. Please show your calculations for the following values and record your final answers in table 2.

a. Height of one carbon atom in cm

b. Volume of a carbon atom in cm^3/atom

c. Volume of a mole of carbon atoms in cm^3/mole

d. Calculated value for Avogadro’s number in atoms/mole

e. Ratio of calculated Avogradro’s number to the actual value for Avogadro’s number

f. Please calculate the percent error for your approximated value of Avogadro’s number

Table 2: Continued Calculations Data Table

Height of one C atom (cm)

Volume of one C atom (cm^3/atom)

Volume of 1 mole of C atoms (cm^3/mole)

Calculated value of Avogadro’s number (atoms/mole)

Ratio of calculated/actual

Percent error

3. Would you consider your percent error high or low?

4. What are some possible causes for the error in your calculated value of Avogadro’s number?