1. Density
of a Gas at
STP
Lesson # 4

2. 1. Calculate the density of N2 at STP.
grams
Density =
litre
Assume that you
have 1 mole of N2
28.0 g
= 1.25 g/L
22.4 L

3. 2. Calculate the density of CO2 at STP.
grams
Density =
litre
Assume that you
have 1 mole of CO2
44.0 g
= 1.96 g/L
22.4 L

4. 3. Calculate the molar mass of gas that weighs 0. 2668 g and has
3. Calculate the molar mass of gas that weighs g and has a STP molar volume of mL. If the gas can be found in Harrison Hot Spring water, determine the gas.
x L
x mol
175.7 mL
= mol
1000 mL
22.4 L
grams
Molar Mass =
mole g
Molar Mass =
mol
= g/mol
= H2S

5. 4. Calculate the volume of O2 gas produced at STP for the
4. Calculate the volume of O2 gas produced at STP for the complete decomposition of 12.5 g HgO if the yield is 45.0 %.
2HgO → 2Hg + O2 12
12.5 g
? L
12.5 g HgO
x 1mole
x 1 mole O2
x L x
= L
216.6 g
2 mole HgO
1 mole

6. 5. Calculate the theoretical yield in litres at STP of CO2 in the
5. Calculate the theoretical yield in litres at STP of CO2 in the reaction of 100. g of Fe2O3. If the actual yield was STP, calculate the percentage yield.
2Fe2O3 + 3C  4Fe + 3CO2
100. g Fe2O3 x 1 mole x 3 mole CO2 x L = L
159.6 g mole Fe2O mole
Percentage yield = L x 100% = %
21.05 L
19.0 L 3 2
100. g
? L