NAME ______________________________________ PER ____ The Mole & Molar Mass
The Mole
The dozen is a unit of counting objects.
1. How many eggs are there in a dozen eggs?
2. How many pencils are in a dozen pencils?
3. Write two general equations to convert a dozen to number of objects and number of objects to
dozen.
4. Using the appropriate conversion factor in #2, convert 3.75 dozen eggs to number of eggs. Show
your work!
5. Using the appropriate conversion factor in #2, convert 248 eggs into dozens of eggs. Show your
work!
Similarly, the mole (mol) is a unit for counting objects. It is especially useful for counting tiny objects like
atoms, molecules, ions, and formula-units.
mole of objects = 6.022 x 1023 objects
6. How many atoms of copper are in 1 mole of copper?
7. How many molecules of water are in 1 mole of water?
8. Write two forms of the conversion factor that will convert one mole to number of objects and
number of objects to moles.
9. Using the appropriate conversion factor in # 8, how many atoms of zinc are in 10.2 moles of zinc?
10. Using the appropriate conversion factor in # 8, find out many moles of water contain 1.51 x 1024
molecules of water.
Fun Questions:
11. A grocery store has 75 dozen packages of hot dogs in stock. If there are 10 hot dogs in each
package, how many moles of hot dogs is this?
12. Estimate the number of times a human heart beats during a life time of 80 years. Express this
number in moles.
a YOUR heart beats per minute _______________
b Show your work for your calculations.
READ THIS!!!
Atoms and molecules are extremely small particles. Scientists have developed a method of measuring
the mass of an atom relative to the mass of a chosen standard atom. This standard atom is the carbon12 atom. The carbon -12 atom has been assigned a mass of exactly 12 amu(s).
13.
What does amu stand for?
14.
How is amu defined?
Using the information given below, answer the following questions.
Hydrogen
Carbon
1
6
H
C
1.00794
12.011
Sodium
11
Na
22.989
15. Given that 1 amu = 1.6606 x 10 -24 g, what is the mass of one mole of hydrogen atoms?
16. What is the unit given to your calculation?
Wait a minute. You have just calculated the molar mass of hydrogen!
17. What is the molar mass of carbon? (Do not forget the unit!)
18. What is the molar mass of sodium?
19. What is the relationship between molar mass in grams per mole (g/mol) and average atomic mass in
amu of each element?
20. Using what you have learned so far, fill the blanks in the boxes below.
Molar mass of Pb =
Molar mass of Si =
Molar mass of Cl =
21. The molar mass of elements that exist as atoms can also be called gram-atomic mass. What is the
name given to the molar masses of substances that exist as molecules?
22. How do you think the molar masses of molecules determined?
23. Calculate the molar mass of water molecules.
24. What is the gram-molecular mass of sulfur dioxide?
25. What is the gram-molecular mass of ammonia (NH3)?
26. What is the molar mass of NaOH?
27. What is the molar mass of Ca(OH)2?
28. What is the molar mass of Ca3(PO4)2?
29. Write the formula for Lithium sulfate. _____________________
30. What is the molar mass of lithium sulfate?
31. How does the following picture prove the law of
conservation of mass? Explain
32. What is the relationship between the mass of the reactants and the mass of the products in a
reaction?
33. 27.0 g of mercuric oxide (a red solid compound) is heated and completely decomposes to give the
elements oxygen and mercury. If 2.0 g of oxygen is produced by this reaction, how much mercury is
produced? SHOW WORK.
34. A substance breaks down into its component elements when it is heated. If 68.0 g of a substance is
present before it is heated, what is the combined mass of the component elements after heating?
SHOW WORK.
35. A 15.236 g sample of iron(III) oxide (Fe2O3) was decomposed into iron (Fe) and oxygen (O2), yielding
10.205 g of iron. How many grams of oxygen were obtained?
a List the Reactant(s)
b List the Product(s)
c
Write the chemical reaction with an arrow separating the reactant(s) from the product(s)
(this is done as an example in this problem to demonstrate how to do this) and then solve
for the mass of oxygen. 2Fe2O3 → 4Fe + 3O2
36. A chemical reaction takes place in an open beaker and combines magnesium metal with
hydrochloric acid. The balanced chemical reaction produces magnesium chloride and hydrogen gas.
Mg + 2 HCl ⇾ MgCl2 + H2↑
You begin with 24 g of magnesium and 36.5 g of HCl and you should have been able to produce 60.5
g of magnesium chloride and hydrogen gas. After the reaction is completed you weigh the open
beaker and find that only 58.5g of products have been made. What happened to the other 2 grams
of product?