1. molecules grams moles finish here start here 1.27 correct units
#16 Find the mass in grams of
4.52 x 10-3 moles of C20H42
Mult. by Molar
Mass
molecules
grams
moles
finish here
start here
282.0 g
1mole
4.52 x 10-3 moles 1 X =
1.27
grams
correct units
for answer here
given

2. Fe(OH)2 molecules grams moles finish here start here 1.27
#17 Calculate the mass in grams of
2.5 moles of Iron (II) hydroxide
Fe(OH)2
Mult. by Molar
Mass
molecules
grams
moles
finish here
start here
2.5 moles 1 g
1mole =
1.27
grams X
correct units
for answer here
given

3. B 10.8 molecules grams moles start here finish here .0343
#18 Find the number of moles in
3.70 x 10-1 (.370) grams of boron
divide by Molar
Mass
molecules
grams
moles
start here
finish here
1 mole B
10.8 g
3.70 x 10-1 grams 1
.0343 X =
moles
correct units
for answer here
given

4. N2O3 molecules grams moles finish here start here .99 correct units
#19 Calculate the number of moles
in 75.0 g of dinitrogen trioxide
N2O3
= 76.0g/mole
divide by Molar
Mass
molecules
grams
moles
finish here
start here
75 g 1
1 mole
76.0 g =
.99
moles X
correct units
for answer here
given

5. 20. What is the volume of these gases
at standard temperature and pressure? (STP)
grams
moles
molecules
start here
mult. by 22.4
volume
finish here
for most
gases:
22.4 Liters
1 mole
a x 10-3 moles CO2
3.20 x 10-3mol 1
22.4 liters
1 mole x =
.0717 liters
b moles N2
82.9 liters N2
22.4 liters
1 mole =
3.7 mole N2 1 x

6. 21. At STP (standard temp. and pressure), what
volume do these gases occupy?
grams
moles
molecules
start here
mult. by 22.4
volume
for most
gases:
22.4 Liters
1 mole
finish here
a moles He
1.25 mol 1
22.4 liters
1 mole x =
28.0 liters He
b moles C2H6
7.5 liters C2H6
22.4 liters
1 mole =
.335 mole C2H6 1 x

7. 80.2 x = 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:
80.2
3.58 g
1 liter
? g
1 mole
22.4 liters
1 mole x =

8. 3.74 x = 23. What is the density of krypton gas at STP? 83.8 g Kr
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?
3.74
83.8 g Kr
1 mole
1 mole
22.4 liters
? g
1liter x =

9. molecules grams moles 24. Describe how to convert between the
mass and the number of moles of a substance
divide. by Molar
Mass
molecules
grams
moles
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

10. 25. What is the volume of one mole of any gas
at STP?
22.4 Liters
1 mole

11. 26. How many grams are in 5.66 moles of CaCO3?
5.66 moles x g = g CaCO3
mole

12. C2H6O 27. Find the number of moles in 508 g of ethanol (C2H6O)?
= 46.0g/mole
508 grams x mole = moles g

13. 28. Calculate the volume, in liters, of 1.50 mol of Cl2 at STP.
1.5 moles x liters = moles
mole

14. 29. The density of an elemental gas is
g/liter at STP. What is the molar
mass of the element?
g x liters = g
1liter mole mole

15. 30. The densities of gases A,B,and C are 1.25
2.86 and respectively. Calculate the
molar mass of each substance. Identify each
substance as ammonia, sulfur dioxide, chlorine,
nitrogen, or methane.
NH3
= 17.0g/mole
SO2
= 64.1g/mole
1.25 g x 22.4 liter =
1 liter mole
28g
mole
Cl2
= 71.0g/mole N2
= 28.0g/mole
CH4
= 16.0g/mole

16. 30. The densities of gases A,B,and C are 1.25
2.86 and respectively. Calculate the
molar mass of each substance. Identify each
substance as ammonia, sulfur dioxide, chlorine,
nitrogen, or methane.
NH3
= 17.0g/mole
SO2
= 64.1g/mole
2.86 g x 22.4 liter =
1 liter mole
Cl2
= 71.0g/mole N2
= 28.0g/mole
64.1g
mole
CH4
= 16.0g/mole

17. 30. The densities of gases A,B,and C are 1.25
2.86 and respectively. Calculate the
molar mass of each substance. Identify each
substance as ammonia, sulfur dioxide, chlorine,
nitrogen, or methane.
NH3
= 17.0g/mole
SO2
= 64.1g/mole
g x 22.4 liter =
1 liter mole
Cl2
= 71.0g/mole N2
= 28.0g/mole
16.0g
mole
CH4
= 16.0g/mole

18. They would have the same number of molecules because the rule states
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.