#16 Find the mass in grams of
4.52 x 10-3 moles of C20H42
Mult. by Molar
Mass
4.52 x 10-3 moles
1
X
282.0 g
1mole
=
1.27
grams
#17 Calculate the mass in grams of
2.5 moles of Iron (II) hydroxide
Fe(OH)
Mult. by Molar
Mass
2.5 moles
1
X
89.8.0 g
1mole
=
225
2
grams
#18 Find the number of moles in
3.70 x 10-1 (.370) grams of boron
B
10.8
divide by Molar
Mass
3.70 x 10-1 grams
1
X
1 mole B =
10.8 g
.0343
moles
#19 Calculate the number of moles
in 75.0 g of dinitrogen trioxide
N2O3
= 76.0g/mole
divide by Molar
Mass
75 g
1
X
1 mole
76.0 g
=
.99
moles
20. What is the volume of these gases
at standard temperature and pressure? (STP)
mult. by 22.4
a. 3.20 x 10-3 moles CO2
3.20 x 10-3mol
1
22.4 liters
1 mole
x
b. 3.70 moles N2
3.7 mole N2
1
x
22.4 liters
1 mole
=.0717 liters
for most
gases:
22.4 Liters
1 mole
82.9
liters
N
2
=
21. At STP (standard temp. and pressure), what
volume do these gases occupy?
mult. by 22.4
a. 1.25 moles He
1.25 mol
1
22.4 liters
1 mole
x
b. .335 moles C2H6
.335 mole C2H6
1
x
22.4 liters
1 mole
for most
gases:
22.4 Liters
1 mole
=28.0 liters He
7.5
liters
C
H
2
6
=
22. A gaseous compound composed of sulfur and
oxygen, which is linked to the formation of acid rain,
has a density of 3.58 g/liter at STP. What is the molar
mass of this gas?
We are given the gas in units of g/liter and need to find the molar mass
which is in units of g/mole. Therefore we need to use the relationship
between liters and moles (22.4 liters/mole) to solve this:
3.58 g
1 liter
x
22.4 liters =
1 mole
80.2? g
1 mole
23. What is the density of krypton gas at STP?
Krypton has like all normal gases 22.4 liters/mole at STP.
Therefore, knowing this and the molar mass of krypton (from the periodic
table) we solve as follows?
83.8 g Kr
x
1 mole
1 mole
=
22.4 liters
3.74?
g
1liter
24. Describe how to convert between the
mass and the number of moles of a substance
divide. by Molar
Mass
multiply by Molar
Mass
To go from grams to moles you need to
divide by the molar mass
To go from moles to grams you need to
multiply by the molar mass
25. What is the volume of one mole of any gas
at STP?
22.4 Liters
1 mole
26. How many grams are in 5.66 moles of
CaCO3?
5.66 moles x
100.1 g
1
1 mole
= 567 g CaCO3
27. Find the number of moles in 508 g
of ethanol (C2H6O)?
C2H6O
= 46.0g/mole
508 grams x
1
1 mole
46.0 g
= 11.0 moles
28. Calculate the volume, in liters, of 1.50 mol
of Cl2 at STP.
1.5 moles
1
x
22.4 liters
1 mole
= 33.6 liters
29. The density of an elemental gas is
1.7824 g/liter at STP. What is the molar
mass of the element?
1.7824 g
1liter
x
22.4 liters
1 mole
= 39.9 g
1 mole
30. The densities of gases A,B,and C are 1.25
2.86 and 0.7134 respectively. Calculate the
molar mass of each substance. Identify each
substance as ammonia, sulfur dioxide, chlorine,
nitrogen, or methane.
SO2
1.25 g x 22.4 liter =
1 liter
1 mole
= 64.1g/mole
28g
mole
Cl2
= 71.0g/mole
NH3
= 17.0g/mole
N2
= 28.0g/mole
CH4
= 16.0g/mole
30. The densities of gases A,B,and C are 1.25
2.86 and 0.7134 respectively. Calculate the
molar mass of each substance. Identify each
substance as ammonia, sulfur dioxide, chlorine,
nitrogen, or methane.
SO2
2.86 g x 22.4 liter =
1 liter
1 mole
64.1g
mole
= 64.1g/mole
Cl2
= 71.0g/mole
NH3
= 17.0g/mole
N2
= 28.0g/mole
CH4
= 16.0g/mole
30. The densities of gases A,B,and C are 1.25
2.86 and 0.7134 respectively. Calculate the
molar mass of each substance. Identify each
substance as ammonia, sulfur dioxide, chlorine,
nitrogen, or methane.
0.7134 g x 22.4 liter =
1 liter
1 mole
16.0g
mole
NH3
SO2
= 17.0g/mole
Cl2
N2
= 64.1g/mole
= 71.0g/mole
= 28.0g/mole
CH4
= 16.0g/mole
31. Three balloons filled with three different
gaseous compounds each have a volume of
22.4 L at STP. Would these balloons have the
same mass or contain the same number of
molecules? Explain
They would have the same number
of molecules because the rule states
that equal volumes of gases contain
equal numbers of molecules.
The masses are probably different
depending on the molar mass of
each gas.