Unit 6b Question Packet Name …………………KEY………………………
Stoichiometry Period ………….
Skills
1. Counting atoms in formulas
2. Counting ions in ionic formulas
3. calculating Molar Mass (GFM)
4. Mole-Mass calculations
5. calculating % composition
6. calculating % composition of a Hydrate
7. Mole to Mole problems
Skill #1: counting atoms in formulas - refer to your notes & RB p. 73 & 87
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.
Formula / Moles of each atom / Total moles of atoms / Formula / Moles of each atom / Total moles of atomsa. / HClO3
M / 1 mol H atoms
1 mol Cl atoms
3 mol O atoms / 5 / f. / CaCl2
I / 1 mol Ca atoms
2 mol Cl atoms / 3
b. / NH4C2H3O2
I / 1 mol N atoms
7 mol H atoms
2 mol C atoms
2 mol O atoms / 12 / g. / Mg3(PO4)2
I / 3 mol Mg atoms
2 mol P atoms
8 mol O atoms / 13
c. / Mg(OH)2
I / 1 mol Mg atoms
2 mol O atoms
2 mol H atoms / 5 / h. / CH3CH2CH3
M / 3 mol C atoms
8 mol H atoms / 11
d. / LiCl·4H2O
H / 1 mol Li atoms
1 mol Cl atoms
8 mol H atoms
4 mol O atoms / 14 / i. / Al(SCN)3
I / 1 mol Al atoms
3 mol S atoms
3 mol C atoms
3 mol N atoms / 10
e. / CH3COOH
M / 2 mol C atoms
4 mol H atoms
2 mol O atoms / 8 / j. / NH4Cl·5H2O
H / 1 mol N atoms
1 mol Cl atoms
14 mol H atoms
5 mol O atoms / 21
Skill #2: counting Ions in Ionic Formulas - 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.
a. / 2.0 mol of NaCl (GFM = 58 g)# moles = given mass
GFM
2.0 = X f
1 58
X = 116 g / c. / 3.25 mol of CuSO4·5H2O
(molar mass = 250. g)
# moles = given mass
GFM
3.25 = X f
1 250.
X = 813 g
b. / 0.50 mol of H2O (GFM = 18 g)
# moles = given mass
GFM
0.5 = X f
1 18
X = 9 g / d. / 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 = 35 f
1 58
X = 0.60 mol / c. / 110. g of CuSO4·5H2O
# moles = given mass
GFM
X = 110. f
1 250.
X = 0.440 mol
b. / 108 g of H2O
# moles = given mass
GFM
X = 108 f
1 18
X = 6.00 mol / d. / 250. g of Cu
# moles = given mass
GFM
X = 250. f
1 64
X = 3.9 mol
#5: calculating % composition – refer to your notes, Table T, and RB p. 90
6. Determine the percent by mass of the given element in the following compounds.
a. / % O in Fe2(SO4)3 (GFM = 400.g)% = part x 100
whole
% O = (12 x 16) x 100
400.
% O = 48.0 % / c. / % O in CuSO4·5H2O (GFM = 250. g)
% = part x 100
whole
% O = (9 x 16) x 100
250.
% O = 57.6 %
b. / % H in H2O (GFM = 18 g)
% = part x 100
whole
% H = (2 x 1) x 100
18
% H = 11 % / d. / % P in (NH4)3PO4 (GFM = 149 g)
% = part x 100
whole
% P = 31 x 100
149
% 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 0.0156 = X x 100 0.058968 = 100 X
whole 3.78 kg 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 0.211 = X x 100 0.028907 = 100 X
whole 13.7 g
X = 0.0289 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.
a. / Na2CO3·10H2O (GFM = 286g)% = part x 100
whole
% H2O = (10 x 18) x 100
286
% H2O = 62.9 % / c. / MgSO4·7H2O (GFM = 246 g)
% = part x 100
whole
% H2O = (7 x 18) x 100
246
% H2O = 51.2 %
b. / Initial mass of hydrate: 9.5 g
Final mass of anhydrous salt: 3.77 g
% = part x 100
whole
% H2O = (9.5 – 3.77) x 100
9.5
% H2O = 60. % / d. / Initial mass of hydrate: 5.3 g
Final mass of anhydrous salt: 4.1 g
% = part x 100
whole
% H2O = (5.3 – 4.1) x 100
5.3
% H2O = 23 %
Skill #7: Mole to Mole problems – refer to your notes & RB p. 93
11. Calculate the number of moles in each problem.
a. Ca + 2H2O à Ca(OH)2 + H2
1 = 2
X 6 X = 3 mol Ca
b. 2N2O5 à 4NO2 + O2
2 = 4
5 X X = 10 mol NO2
c. 2Li+ H2SO4 à Li2SO4 + H2
2 = 1
X 3.3 X = 6.6 mol Li