CH 115 Fall 2014
Worksheet 17
1. What number/factor do you use and how do you use it to complete each of the
following conversions?
a). Moles to atoms – multiply by Avogadro’s number (6.02 x 1023)
b). Moles to particles – same as a
c). Moles to molecules – same as b
d). Atoms to moles – divide by Avogadro’s number
e). Moles to grams – multiple by molar mass (from periodic table)
f). Grams to moles – divide by molar mass
2. The number of atoms in a mole of any pure substance is called Avogadro’s number
(6.02 x 1023).
3. When compared with a mole of oxygen, a mole of sulfur contains how many atoms?
Both contain 6.02 x 1023 atoms.
4. A sample of tin contains 3.01 x 1023 atoms. What is the mass of the sample?
Atoms  moles  grams (2 step problem)
3.02 x 1023 atoms / 6.02 x 1023 = 0.5016611296 mol Sn
0.5016611296 mol * 118.71 g/mol = 59.55 grams Sn
5. How many moles of NO2 are present in 114.95 g?
Grams  moles (1 step problem)
114.95 g NO2 / 46 g/mol = 2.50 mol NO2
6. How do you calculate percent composition? What is the percent composition, by
mass, of each element in CO?
% composition of element X = (molar mass of element X / total molar mass of
compound) x 100
% composition of C in CO = (12.01/28) x 100 = 42.9%
% composition of O in CO = (16/28) x 100 = 57.1%
7. Which of the following weighs more?
a). 1 mole of hydrogen
b). 0.25 moles of He
c). 0.1 mol of Ne
d). 0.2 mol of C
8. How many moles are present in 9.03 x 1024 atoms of a compound?
Atoms  moles
9.03 x 1024 atoms / 6.02 x 1023 = 15 moles
9. What is the percentage composition, by mass, of oxygen in H2O?
% composition of O in H2O = (16/18) x 100 = 88.9%
10. How many molecules are in 23 moles of oxygen gas?
Moles  molecules
23 moles * 6.02 x 1023 molecules = 1.38 x 1025 molecules
CH 115 Fall 2014
11. How many grams are in 8.2 x 1022 molecules of N2I6?
Molecules  moles  grams
8.2 x 1022 molecules / 6.02 x 1023 = 0.1362126246 moles
0.1362126246 moles * 789.4 g/mol = 107.53 grams N2I6
Worksheet 17