In this lab, students determine the number of moles of chalk used to write their name, the moles of sucrose ingested while chewing gum, and the moles of alcohol evaporated when using hand sanitizer.
By the end of this lesson, students should be able to
- calculate the molar mass of a substance.
- calculate the number of moles of a compound in a given mass.
- calculate the number of molecules of a compound in a given mass.
This lesson supports students’ understanding of
- Mole concept
- Molar mass
Teacher Preparation: 15 minutes
Lesson: 1–2 class periods
For each group:
- Piece of chalk
- Piece of gum (not sugar-free)
- Hand sanitizer
- Food in the lab should be considered a chemical not for consumption.
- Make sure that the gum used is not sugar-free.
- This lab asks students to write on their desks in chalk – you may prefer to take your class outside to write on the sidewalk.
- Once the gum has been massed, instruct students to discard of the gum. Gum should never be chewed in the lab.
For the Student
Words are often used to describe numbers:
Pair =2; Dozen = 12; Score 20; Century = 100; Ream = 500;
Mole (also called Avogadro’s number)= 602,000,000,000,000,000,000,000 à 6.02 X 1023
A hydrogen atom weighs 1.66 x 10-24 g. Is it realistic for you to see or work with only a dozen atoms? No way! The most exact balances in a high school chemistry lab only measures to 10-3 g. Therefore, you need to work with large numbers of atoms and “moles” allow you to do that easily.
- Which is more convenient?
- (A) Go in the store and count out 36 eggs
- (B) Go in the store and count out three one-dozen cartons of eggs.
- Which is more convenient?
- (A) Burn 1 mole of carbon with 2 moles of sulfur and measure the mass of the product.
- (B) Burn 602,000,000,000,000,000,000,000 atoms of carbon with 1,204,000,000,000,000,000,000,000 atoms of sulfur and measure the mass of the product.
You may be surprised to find out that Avogadro did not calculate Avogadro’s number, and the idea of a mole did not exist in his lifetime. He hypothesized that any two gases at the same volume, temperature, and pressure, contain the same number of molecules. This set a foundation for finding what that number was, and that is why 6.02 x 1023 is named after him.
Part I: How much chalk is needed to write your name?
- Find the mass of a piece of chalk. M0 =_________ g
- Write your name on the table using the chalk: first name, middle initial, and last name. Yes, you may “decorate” it a bit.
- Find the mass of the chalk again so you can determine how much was used to write your name. Mf =_________ g
- Determine the mass of chalk used to write your name. ΔM = _________ g
- Chalk is pure calcium carbonate. Write its chemical formula and use the periodic table to calculate its molar mass (g/mole).
- Calculate the number of moles of calcium carbonate that were used to write your name.
- Calculate the number of molecules of calcium carbonate that were used.
- How many times would you have to write your name in order to use up 1.00 mole of calcium carbonate?
Part II: How much sucrose do you ingest when chewing a piece of gum?
- Collect data similar to what you did with chalk but for gum. (Once you find the final mass of the gum, it must be discarded.) M0 = ___________g Mf = ___________g ΔM = _________ g
- Sugar is sucrose, which has a chemical formula of C12H22O11. Use the periodic table to calculate its molar mass (g/mole).
- Calculate the number of moles of sucrose that were ingested.
- Calculate the number of molecules of sucrose that were ingested?
- How many pieces of gum would you have to chew in order to ingest 1.00 mole of sucrose?
Part III: How much alcohol evaporates when using hand sanitizer?
- As a class, find the mass of “one dose” of hand sanitizer. _____________ g.
- If 62% of the dose is ethanol (or ethyl alcohol) and if all of this alcohol evaporates, calculate the mass of ethanol in one dose that will change into a vapor: _______________ g.
- Apply and use one dose of hand sanitizer.
- The chemical formula for ethanol is C2H6O. Use the periodic table to calculate its molar mass.
- Calculate the number of moles of ethyl alcohol in the one dose.
- Calculate the volume of ethyl alcohol that evaporated (in mL). 1 L = 1,000 mL and 1 mole of ANY gas at STP = 22.4 L.
- How many “doses” would be needed to fill an average trash bag (50 L) full of ethanol vapor?