Chem Gas Worksheet 5 WITH ANSWERS.
Block: ____ Teacher: ________________ Name: ___________________________________
I. Molecular mass and gas density.
a. 5.87 g of gas occupy 1.45 L at 28°C, 98.8kPa. (i) How many moles of gas is it? (ii) What is the
molecular weight of the gas? (Hint: What are the units of molecular weight?)
PV = nRT
98.8 x 1.45 = n x 8.314 x 301
n = 0.0572
i.
5.87 g / 0.0572 mol = 103 g/mol
0.0572 mol
ii. 103 g/mol
b. 15.3 g of gas occupied 996 ml at 75°C, 198kPa. What is the molecular mass of the gas?
198 x 0.996 = n x 8.314 x 348
n = 0.0682 mol
15.3 g / 0.0682 mol = 224 g/mol
224 g/mol
c. What is the molecular weight of a gas which has a density of 3.78 g/L at 95°C, 920mmHg?
(Hint: 1L = ?g, ?mol)
3.78 g/L x 62.36 x 368°K
M = -------------------------------------- = 94.3 g/mol
920 mmHg
94.3 g/mol
d. What is the density of CH4(g) at SATP? (Hint: 1 mol = ?g, ?L)
d x 8.314 x 298
16.0 = ----------------------------100
d = 0.646 g/L
0.646 g/L
e. What is the density of SO2(g) at 822K, 0.278atm?
d x 0.8206 x 822
64.1 = ----------------------------0.278
d = 0.264 g/L
0.264 g/L
f. What is the density of C2H6(g) at -113°C, 9.25 psi?
d x 8.314 x 160
30.1 = ----------------------------------------9.25 psi x (100kPa / 14.5 psi)
d = 1.44 g/L
1.44 g/L
g. 87.3 cm3 of gas was collected over water at 22°C, atmospheric pressure 96.8kPa. The gas
was found to weigh 0.350 g. What was the molecular weight of the gas?
(.350 / 0.0873) x 8.314 x 295
M = ----------------------------------------- = 102 g/mol
96.8
102 g/mol
J. Stoichiometry.
a. How many liters of O2 gas, measured at SATP, are needed to completely burn 3.0 L of CH4(g)
at SATP? How many liters of CO2(g) at SATP are produced? (WRITE BALANCED EQUATION
FIRST!)
CH4 + 2 O2 -> CO2 + 2 H2O
3.0 L CH4 x (2 L O2 / 1 L CH4) = 6.0 L O2
6.0 L O2
3.0 L CH4 x (1 L CO2 / 1 L CH4) = 3.0 L CO2
3.0 L CO2
b. How many liters of hydrogen gas are needed to produce 6.295 L of ammonia, NH3, both
measured at the same temperature and pressure?
N2 + 3 H2 -> 2 NH3
6.295 L NH3 x (3 L H2 / 2 L NH3) = 9.443 L H2
9.443 L H2
c. What volume of oxygen gas, measured at 35°C and 115 kPa, is required to completely burn
50.0 g of Mg?
O2 + 2 Mg -> 2 MgO
50.0 g Mg x (1 mol Mg / 24.3 g Mg) x (1 Mol O2 / 2 Mol Mg) = 1.03 Mol O2
115 x V = 1.03 x 8.314 x 308
V = 22.9 L O2
22.9 L O2
d. Your “Mass Relations in Chemical Reactions” lab reacted sodium carbonate with hydrochloric
acid, producing carbon dioxide, water, and sodium chloride. If you used exactly 2.00 g of sodium
carbonate and excess HCl, what volume of CO2 would be produced, measured at 22°C,
752mmHg?
Na2CO3 + 2 HCl -> CO2 + H2O + 2 NaCl
2.00 g x 62.36 x 295
106 = --------------------------------752 x V
V = 0.462 L = 462 cm 3
462 cm3 CO2
e. Aluminum reacts with sulfuric acid in a single replacement reaction. Hydrogen gas is one of
the products. What volume of hydrogen gas, collected over water at 25°C and at an atmospheric
pressure of 766mmHg, could be obtained by the reaction of 3.25 g of Al with 22.5 g of H2SO4?
(Hint: Look in your notes for “limiting reagent” problems!)
2 Al + 3 H2SO4 -> Al2(SO4)3 + 3 H2
(3.25 / 27.0) x (3 mol H2 / 2 mol Al) x 62.36 x 298°K
V = ----------------------------------------------------------------------- = 4.52 L
766 mmHg - 23.70 mmHg
4.52 L H2