Weighing Gases Lesson 8

1
Weighing GasesLesson 8
2
The electrolysis of water is used to generate
0.250 g of H2 (g). If the hydrogen was generated
at a rate of 1.500 amps over a period of 4.46625
hours, calculate Avogadros number (the number of
atoms of H in 1 gram) 1 amp is defined as the
number of coulombs per second. There are 6.24 x
1018 electrons in a coulomb. It takes 1 electron
to make 1 H atom
x 1 at H
x 6.24 x 1018 el
x 1.500 coul
4.46625 h
x 60 min
x 60 s
1 el
1 coul
s
1 h
1 min
1.505 x 1023 at H
6.02 x 1023 at H
0.250 g
3

• Avogadros hypothesis states that equal volumes
  of gases have the same number of
• particles.

If you weigh the volumes
1.0 L of CO2
2.56 g



22
0.116 g
1.0 L of H2
Note that the mass ratio is the same as the molar
mass ratio

CO2
44 g/mole
22
H2
2.02 g/mole
4

• A volume of an unknown gas weighs 0.563 g. An
  equal volume of H2 gas weighs
• 0.01774 g. Calculate the molar mass of the
  unknown gas.

Gas X
0.563 g
31.7
x 2.02 g/mole
64.1 g/mole
H2
0.01774g
This means the molar mass of gas X is 31.7 x
heavier than H2
If the gas is a byproduct of burning coal and
causes acid rain, what is the gas?
SO2
5

• A volume of an unknown gas weighs 2.365g. An
  equal volume of C2H6 (ethane) gas
• weighs 17.7g. Calculate the molar mass of the
  unknown gas.

4.02 g/mole
x 30.06 g/mole
0.1336
2.365 g
Gas X
17.7 g
C2H6
This means the molar mass of gas X is 0.1336 x
C2H6
If the unknown gas is an element, what gas is it?
Helium
Rock me Avogadro