Review Self-Quiz for
Stoichiometry
1. Write the formula for a
compound made from sodium
and chlorine. Na and Cl → NaCl
2. Write a chemical reaction for
the following: Na reacts with
chlorine, Cl2, to form sodium
chloride. 2 Na + Cl2 → 2 NaCl
3. Find the gram formula weight
of Cl2.
2 Cl = 35 x 2 = 70 g/mole
4. Find the gram formula weight
of NaCl Na = 23
+
Cl = 35
58 g/mole
-
Basic Skills
•
Looking up the mass of elements in
the periodic table:
6.941 amu or g/mole
1. Li
22.989 768 amu or g/mole
2. Na
3. Ca
40.078 amu or g/mole
63.546 amu or g/mole
4. Cu
55.847 amu or g/mole
5. Fe
14.006 74 amu or g/mole
6. N
15.999 4 amu or g/mole
7. O
35.452 7 amu or g/mole
8. Cl
32.066 amu or g/mole
9. S
10.Br 79.904 amu or g/mole
Basic Skills needed
• Finding the gram
formula mass
• separate the elements
• look up the atomic
mass in the periodic
table
• figure out how many
of each atom are in
the formula
• subtotal the masses
of the elements
• Find the total mass of
the compound.
ex:
2 Al
3 S
12 O
Al2(SO4)3
27
32
16
x 2 = 54
x 3 = 96
x 12 = 192
= 342g
mole
Stoichiometry
(Chapter 9 Black Book)
• READ and UNDERLINE important
parts of the problem.
• Write Balanced Formulas
•+=-
• Write Balanced Equations
• use coeficients to make atoms in reactants =
same atoms in products
• Find moles of “known”
• Find moles of “unknown”
• Make sure the questions are
answered.
Your Turn: Find the gfw for
the following compounds:
1.
2.
3.
4.
5.
6.
7.
Ca (OH)2
NaOH
CaCl2
MgF2
K2O
Zn3(PO4)2
NaCl
answers:
Ca(OH)2 = 74 g/mole
NaOH
= 40 g/mole
CaCl2
= 110 g/mole
MgF2
= 62 g/mole
K2 O
= 94 g/mole
Zn3(PO4)2= 385 g/mole
NaCl
= 58 g/mole
What mass of NH4Cl
__________________________________
can be produced
from _______________________________
7.87 grams of NH3.
NH3 + HCl → NH4Cl
First, identify knowns and unknowns
• Known: 7.87 g NH3
• Unknown: ? g NH4Cl
Next, to convert the mass of NH3 to moles
you must find the gram formula weight (gfw)
of ammonia, NH3
N = 14
3H = 1
=14
x3
=3
-----17 g/mole NH3
What mass of NH4Cl
__________________________________
can be produced
from _______________________________
7.87 grams of NH3.
NH3 + HCl → NH4Cl
• Known: 7.87 g NH3 = ? mole
• Unknown: ? g NH4Cl
Now that you know that NH3 has a gfw (gram
formula weight of 17 g/mole, you convert
grams ammonia to moles of ammonia.
7.87 g NH3
-----17 g/mole NH3
= 0.463 moles NH3
What mass of NH4Cl
__________________________________
can be produced
from _______________________________
7.87 grams of NH3.
NH3 + HCl → NH4Cl
• Known: 7.87 g NH3 = 0.463 mole
• Unknown: ? g NH4Cl = .463 mole
Now that you know that we have 0.463 mole
of NH3, we use the balanced chemical
equation to determine that for every 1 mole
of NH3 we make 1 mole of NH4Cl.
0.463 moles NH3
1 mole NH4Cl
----------------------1 mole NH3
= 0.463 moles NH4Cl
What mass of NH4Cl
__________________________________
can be produced
from _______________________________
7.87 grams of NH3.
NH3 + HCl → NH4Cl
• Known: 7.87 g NH3 = 0.463 mole
• Unknown: ? g NH4Cl = 0.463
mole
Now that you know that we have 0.463 mole
of NH4Cl, we find the gfw (gram formula
weight) of NH4Cl.
4
N = 14
H= 1
Cl = 35
=14
x4 =4
=35
53 g/mole NH4Cl
What mass of NH4Cl
__________________________________
can be produced
from _______________________________
7.87 grams of NH3.
NH3 + HCl → NH4Cl
• Known: 7.87 g NH3 = 0.463 mole
• Unknown: ? g NH4Cl = 0.463 mole
Now that you know that we have 0.463 mole
of NH4Cl, and the gfw (gram formula
weight) of NH4Cl is 53g/mole, we can
calculate the number of grams ammonium
chloride.
(0.463 mole NH4Cl) 53 g/mole NH4Cl
= 24.5 g NH4Cl
Try another:
• What mass of Mg(OH)2 will react
with 1.20 grams of HCl.
•1Mg(OH)2 + 22 HCl -> MgCl2 + 2 H2O
0.97 grams
1.20 g
 (36 g/mole HCl)
x 58g/mole
0.033 moles HCl
0.017
Mg = 24
2O = 32
2H = 2
= 58g/mole
Try another:
• What mass of Ca(OH)2 will react
with 2.40 grams of HCl.
•1Ca(OH)2 + 22 HCl -> CaCl2 + 2 H2O
2.5 grams
2.40 g
 (36 g/mole HCl)
x 74 g/mole
0.067 moles HCl
0.033
Ca = 40
2O = 32
2H = 2
= 74g/mole
Try another:
• What mass of CaCl2 will form
when 2.40 grams of HCl react.
• Ca(OH)2 + 22 HCl ->1CaCl2 + 2 H2O
2.40 g
3.7 g CaCl2
?
 (36 g/mole HCl)
Ca
2Cl
= 40
= 70
= 110g/mole
x 110 g/mole CaCl2
0.067 moles HCl
0.033 moles CaCl2