Unit 6b Question Packet
Stoichiometry
Name …………………KEY………………………
Period ………….
SKILLS
1.
2.
3.
4.
COUNTING ATOMS in formulas
COUNTING IONS in ionic formulas
calculating MOLAR MASS (GFM)
MOLE-MASS calculations
SKILL #1:
5. calculating % COMPOSITION
6. calculating % COMPOSITION OF A HYDRATE
7. MOLE TO MOLE problems
- refer to your notes & RB p. 73 & 87
COUNTING ATOMS IN FORMULAS
1. Fill in the table below. Put an “M” if the substance is molecular/covalent, an “I” if ionic,
and an “H” if a hydrate.
Total
Total
Formula
Moles of each
moles of
Formula
Moles of each
moles of
atom
atoms
atom
atoms
HClO3
CaCl2
1 mol H atoms
1 mol Ca atoms
a.
5
f.
3
1 mol Cl atoms
2 mol Cl atoms
M
I
3 mol O atoms
NH4C2H3O2
b.
I
Mg(OH)2
c.
I
LiCl4H2O
d.
e.
SKILL #2:
H
CH3COOH
M
1 mol N atoms
7 mol H atoms
2 mol C atoms
2 mol O atoms
1 mol Mg atoms
2 mol O atoms
2 mol H atoms
1 mol Li atoms
1 mol Cl atoms
8 mol H atoms
4 mol O atoms
Mg3(PO4)2
12
5
g.
h.
I
CH3CH2CH3
M
Al(SCN)3
14
i.
I
NH4Cl5H2O
2 mol C atoms
4 mol H atoms
2 mol O atoms
8
j.
counting IONS IN IONIC FORMULAS
H
3 mol Mg atoms
2 mol P atoms
8 mol O atoms
13
3 mol C atoms
8 mol H atoms
11
1 mol Al atoms
3 mol S atoms
3 mol C atoms
3 mol N atoms
1 mol N atoms
1 mol Cl atoms
14 mol H atoms
5 mol O atoms
10
21
- refer to your notes, RB p. 73, and Table E!
2. Complete the table below. Use Table E!!!
Ionic
Compound
Cation
(+ ion)
Anion
(- ion)
Total moles
of ions
Ionic
Compound
Cation
(+ ion)
Anion
(- ion)
Total moles
of ions
a.
NH4C2H3O2
NH4+
C2H3O2–
2
e.
CaF2
Ca2+
2 F–
3
b.
Ba(NO3)2
Ba2+
2 NO3–
3
f.
Al2O3
2 Al3+
3 O2–
5
c.
Li2CO3
2 Li+
CO32–
3
g.
KMnO4
K+
MnO4–
2
d.
NaHCO3
Na+
HCO3–
2
h.
(NH4)3PO4
3 NH4+
PO43–
4
SKILL #3:
calculating MOLAR MASS (GFM)
- refer to your notes, the P.T., & RB p. 88
3.
Calculate the gram-formula mass for each compound below. Show your work.
a. Fe2(SO4)3
b.
C8H18
add atomic masses on P.T.
add atomic masses on P.T.
#
Mass
#
Mass
Fe
2 x 56 = 112
C
8 x 12 = 96
S
3 x 32 = 96
H
18 x 1 = 18
O
12 x 16 = 192
114 g
400 g
e. (NH4)3PO4
f.
MgSO47H2O
add atomic masses on P.T.
add atomic masses on P.T.
#
Mass
#
Mass
N
3 x 14 = 42
Mg
1 x 24 = 24
H
12 x 1 = 12
S
1 x 32 = 32
P
1 x 31 = 31
O
11 x 16 = 176
O
4 x 16 = 64
H
14 x 1 = 14
149 g
246 g
c. C11H22O11
d.
NH4Cl3H2O
add atomic masses on P.T.
add atomic masses on P.T.
#
Mass
#
Mass
C
11 x 12 = 132
N
1 x 14 = 14
H
22 x 1 = 22
H
10 x 1 = 10
O
11 x 16 = 176
Cl
1 x 35 = 35
330 g
O
3 x 16 = 48
107 g
SKILL #4:
MOLE-MASS calculations
– refer to your notes, Table T, and RB p. 89
4. Determine the mass of each of the following quantities. Show your work.
3.25 mol of CuSO45H2O
a.
2.0 mol of NaCl (GFM = 58 g)
c.
# moles = given mass
(molar mass = 250. g)
GFM
# moles = given mass
GFM
2.0
= X f
3.25
= X f
1
58
1
250.
b.
X = 116 g
0.50 mol of H2O (GFM = 18 g)
# moles = given mass
GFM
0.5
= X f
1
18
X =9g
d.
X = 813 g
0.75 mol of Cu (mass of 1 mol = 64 g)
# moles = given mass
GFM
0.75
= X f
1
64
X = 48 g
5. Determine the number of moles in each of the following quantities. Use the GFM’s given
in #4 to solve. Remember GSSC.
a.
35 g of NaCl
# moles = given mass
GFM
X
1
=
c.
110. g of CuSO45H2O
# moles = given mass
GFM
35 f
58
X
1
X = 0.60 mol
b.
=
d.
250. g of Cu
# moles = given mass
GFM
108 f
18
X
1
X = 6.00 mol
#5:
110. f
250.
X = 0.440 mol
108 g of H2O
# moles = given mass
GFM
X
1
=
=
250. f
64
X = 3.9 mol
– refer to your notes, Table T, and RB p. 90
calculating % COMPOSITION
6. Determine the percent by mass of the given element in the following compounds.
a.
% O in Fe2(SO4)3
(GFM = 400.g)
c. % O in CuSO45H2O (GFM = 250. g)
% = part x 100
% = part x 100
whole
whole
%O
%O
b.
=
(12 x 16)
400.
x 100
= 48.0 %
%O
% H in H2O
(GFM = 18 g)
% = part x 100
whole
%H
%O
=
(2 x 1)
18
d.
x 100
=
(9 x 16)
250.
x 100
= 57.6 %
% P in (NH4)3PO4
(GFM = 149 g)
% = part x 100
whole
%P
=
31 x 100
149
% H = 11 %
% P = 21 %
7. A substance known as heavy water can be obtained from ordinary water and could be
a significant source of energy in the future. Heavy water contains deuterium, H-2. Instead
of the two hydrogen atoms in a typical water molecule, a heavy water molecule has
two deuterium atoms. In 3.78 kilograms of ordinary water, the percent composition by
mass of heavy water is approximately 0.0156%.
Calculate the mass of heavy water in a 3.78-kilogram sample of ordinary water. Your
response must include both a correct numerical setup and the calculated result. [2]
% heavy =
X x 100
whole
0.0156 = X x 100
3.78 kg
0.058968 = 100 X
X = 5.90 x 10-4 kg
8. In a 13.7-g sample of carbon, the percent composition by mass of carbon-14 is
approximately 0.211%. Calculate the mass of carbon-14 in this sample.
% C-14 =
X
x 100
whole
0.211 = X x 100
13.7 g
0.028907 = 100 X
X = 0.03 g
9. A sample of boron is approximately 3.14% B-6 by mass. The mass of just B-6 in this sample
is 0.376 g. Calculate the total mass of the sample.
% B-6 = part
x 100
3.14 = 0.376 x 100
3.14 X = 37.6
X
X
X = 12.0 g
SKILL #6:
calculating % COMPOSITION OF A HYDRATE
– refer to your notes, Table T, and RB p. 90-91
10. Determine the percent by mass of water in the following hydrates.
Na2CO310H2O (GFM = 286g)
a.
c. MgSO47H2O (GFM = 246 g)
% = part x 100
% = part x 100
whole
whole
% H2O =
(10 x 18)
286
x 100
% H2O =
% H2O = 62.9 %
b.
=
(9.5 – 3.77)
9.5
d.
Initial mass of hydrate: 5.3 g
Final mass of anhydrous salt: 4.1 g
% = part x 100
whole
x 100
% H2O
% H2O = 60. %
Ca + 2H2O  Ca(OH)2 + H2
1 =
X
b.
=
4
X
d.
=
x 100
3H2 + N2  2NH3
1 =
2.8
e.
1
3.3 X = 6.6 mol Li
2
X
X = 5.6 mol NH3
2C2H2 + 5O2  4CO2 + 2H2O
2
X
X = 10 mol NO2
2Li+ H2SO4  Li2SO4 + H2
2
X
(5.3 – 4.1)
5.3
– refer to your notes & RB p. 93
X = 3 mol Ca
2N2O5  4NO2 + O2
2
5
c.
2
6
=
% H2O = 23 %
SKILL #7:
MOLE TO MOLE problems
11. Calculate the number of moles in each problem.
a.
x 100
% H2O = 51.2 %
Initial mass of hydrate: 9.5 g
Final mass of anhydrous salt: 3.77 g
% = part x 100
whole
% H2O
(7 x 18)
246
=
5
11.5
X = 4.6 mol C2H2
f.
CH4 + 2O2  CO2 + 2H2O
2 =
7.4
1
X
X = 3.7 mol CO2