End of Section Questions
**In the final resource, a fully worked out answer for each problem will be available to the instructor**
1. Determine the molar mass of each substance:
2. In their powdered form, limestone and aspirin may look identical.
UNIT 5: CHEMICAL REACTIONS
SECTION 5C: THE MOLE
1. What is a mole?
a. Reading: Intro to Mole
b. Infographic: Mole
c. Developing Skills: Molar Mass
d. Reading: Measure of a Mole
e. AACT Lab: Calculating Moles
2. Why do chemists use it?
a. Reading: Empirical Formula
b. Reading: % Composition
c. Developing Skills: % Composition
d. AACT Activity: Empirical Formula End of Section Questions
4. If you could spend a billion dollars ($1x109) per second, how many years would it take to spend one mole of dollars?
a. Write its name and chemical formula.
b. Is the mineral’s chemical formula its molecular or empirical formula? Explain how you know.
c. Determine its molar mass.
d. Find the percent composition by mass of each element.
a. What is its empirical formula?
b. Vinegar contains two carbons. What is its molecular formula? And what is vinegar’s molecular mass?
a. What is the empirical formula of octane?
b. If its molecular mass is 114 g/mol, what is its molecular formula?
c. Do you notice anything between the molecular formula and the common name of the compound?
8. Calculate the percent composition of the U.S. quarter, which has a mass of 5.670 g and contains 5.198 g copper and 0.472 g nickel.
9. There are thousands of tons of gold in sea water. Explain why it is unlikely that ocean water will ever be “mined” for gold.
10. A 10.0-g sample of sports drink powder contains 7.0 g sucrose (C12H22O11), 2.8 g glucose (C6H12O6), and 0.20 g sodium chloride (NaCl). Calculate the composition (by mass) of
e. Carbon (careful, this one is tricky!)
11. In your laboratory experiences, you may encounter compounds called hydrates. Here are some examples of hydrates:
Na2S2O3·5H2O CaSO4·2H2O Na2CO3·10H2O
a. Why are these compounds called hydrates?
b. Calculate the molar mass of each hydrate.
c. Calculate the percent water of each hydrate.
d. Although hydrates contain significant amounts of water, they are found as dry solid substances at room temperature. How is this possible?
a. Why don't we use moles as our standard way of communicating chemical quantities?
b. Stevia is a sugar substitute; its chemical formula is C38H60O18. If you have a 1-gram packet, how many molecules of Stevia do you have? How does that compare to the sugar packet you measured in the lab?
a. Assuming all quarters have the same mass, if you have a full roll of quarters with a mass of 100 g, how much does each quarter weight?
b. Pennies are not as simple -- pennies made before 1982 have a different mass than pennies made after 1982. If pre-1982 pennies have a mass of 3.11 g and post-1982 pennies have a mass of 2.5 g, how many of each do you have if a roll of pennies weighs 142 g?
c. Do some research to figure out how much rolls of nickels and dimes should weigh.
d. Use this analogy to equate the terms molar mass, number of particles, and mass to the coins.