Unit 7 Compound Stoichiometry Review
Name: ____________________________
Use the following Phrase Bank to answer questions 1- 5.
Phrase Bank
the actual # of atoms present in one molecule
the percentages of atoms present in one molecule
the total # of atoms or ions
the # of atoms of a substance
formula for all compounds
6.02 x 10 23 particles of a substance
the maximum # of grams in a substance
gram of the element
mole of the element
maximum # of atoms in a compound
lowest whole # ratio of atoms
atom of the element
atom of the element
liter of the element
the mass of a substance
the formula of a substance
1. A mole is a unit defined to be 6.02 x 1023 particles of a substance.
2. The molar mass of an element is the mass of one mole of the element.
3. What information is given to you in the empirical formula? lowest whole # ratio of atoms.
4. What do the subscripts represent in a molecular formula? The actual # of atoms present in
one molecule.
Label the following as true or false.
5. false An empirical formula can never be the same as the molecular formula. Why?
A. because the molecular formula always contains less atoms than the empirical formula.
B. because the molecular formula always contains more atoms than the empirical formula.
C. because the molecular formula always contains the same number of atoms as the
empirical formula.
D. because the molecular formula can contain the same number of atoms as the empirical
formula.
6. false One mole of O2 has a greater mass than 1 mole of Na2O. The molar mass of O2 (32.00
g/mol) is less than the molar mass of Na2O (61.98 g/mol).
7. false One mole of H2 has molecules than 1 mole of Na2O. They have the same # of
molecules/formula units since there are 6.02 particles in one mole.
8. false One molecule of H2 has more atoms than 1 molecule of SiO2. SiO2 has 3 atoms for each
molecule – 1 silicon and 2 oxygens. Each molecule of H2 has 2 atoms of hydrogen.
9. Find the molar mass of Al2(SO3)3
Al: 2 (26.98 g/mol) =
53.96 g/mol
S: 3 (32.07 g/mol) =
96.21 g/mol
O: 9 (16.00 g/mol) = + 144.00 g/mol
294.17 g/mol
10. How many moles are in 2.4g of carbon dioxide (CO2)?
2.4 g CO2
1 mol CO2
44.01 g CO2
= 0.055 mol CO2
11. What is the mass in grams of 0.75 moles of water?
0.75 mol H2O
18.02 g H2O
1 mol H2O
= 14 g H2O
12. How many atoms are in 6.3 moles of calcium?
6.3 mol Ca
6.02 x 1023 atoms Ca
1 mol Ca
= 3.8 x 1024 atoms Ca
13. Calculate the number of moles there are in 4.5 x 1026 molecules of sulfur dioxide (SO2).
4.5 x 1026 mlcl SO2
1 mol SO
6.02 x 1023 mlcl SO2
= 750 mol SO2
14. How many formula units are there in 1.6 grams of sodium bromide (NaBr)?
1.6 g NaBr
1 mol NaBr
102.89 g NaBr
6.02 x 1023 f.u. NaBr
1 mol NaBr
= 9.4 x 1021 f.u. NaBr
15. Calculate the mass in grams of 3.5 x 1025 atoms of lithium.
3.5 x 1025 atoms Li
1 mol Li
6.02 x 1023 atoms Li
6.94 g Li
1 mol Li
= 400 g Li
16. How many sodium atoms are there in 26.3 grams of sodium oxide (Na 2O)?
26.3 g Na2O
1 mol Na2O
61.98 g Na2O
2 mol Na
1 mol Na2O
6.02 x 1023 atoms Na
1 mol Na
= 5.11 x 1023 atoms Na
17. Calculate the percent composition of sodium and oxygen in sodium oxide (Na 2O).
Molar Mass Na2O:
% Na:
2(22.99) + 1(16.00) = 61.98 g/mol
2(22.99)
61.98
% O:
1(16.00)
61.98
Check:
X 100
X 100
= 74.19% Na
= 25.81% O
All percentages should add to equal 100%
74.19% + 25.81% = 100% 
18. What is the empirical formula of a compound that contains 81.68% carbon and 18.32%
hydrogen?
%→
mass
C
81.68g
H
18.32g
Mass → mole
81.68 g C
18.32 g H
1 mol C
12.01 g C
1 mol H
1.01 g H
= 6.8010 mol C
18.1386 mol H
Divide by
smallest
6.8010
=1
6.8010
18.1386
= 2.67
6.8010
Multiply ‘till
whole
x3=3
x3=8
C3H8
19. What is the molecular formula of a hydrocarbon that has an empirical formula of CH 4 and a
molecular mass (molar mass of molecule) of 48.15 g/mol?
MMmlcl
MMemp
=
48.15
16.05
(CH4) x 3 = C3H12
=3