1. Weighing Gases Lesson 8

2. The electrolysis of water is used to generate 0. 250 g of H2 (g)
The electrolysis of water is used to generate g of H2 (g). If the hydrogen was generated at a rate of amps over a period of hours, calculate Avogadro’s number (the number of atoms of H in 1 gram)
1 amp is defined as the number of coulombs per second.
There are x electrons in a coulomb.
It takes 1 electron to make 1 H atom h
x 60 min
x 60 s
x coul
x x el
x 1 at H
1 el
1 h
1 min s
1 coul
= x at H
= x at H
0.250 g

3. Avogadro’s 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
A volume of an unknown gas weighs g. An equal volume of H2 gas weighs
g. Calculate the molar mass of the unknown gas.
Gas X
= g =
x g/mole
= g/mole H2 g
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
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.
Gas X
= g =
x g/mole
= g/mole
C2H6
17.7 g
This means the molar mass of gas X is x C2H6
If the unknown gas is an element, what gas is it?
Helium
Rock me Avogadro