14.1. The Ideal Gas Law http://www.ck12.org
Check Your Understanding
The atomic mass of aluminum oxide Al 2 O 3 (2 aluminum atoms and 3 oxygen atoms) is 102u.
a. What is the mass of one mole of aluminum oxide?
Answer: 102 grams
b. What is the molar mass of aluminum oxide?
Answer: By definition, the mass of one mole of a substance is its molar mass: 102 grams
c. You are given 230 grams of aluminum oxide. How many molesnof aluminum oxide do you have?
Answer:n= 102230 gg
mol
= 2. 25 mol
d. What is the atomic mass of aluminum?
Answer: As cited above, one atom of oxygen has atomic mass 16u.
Therefore, three oxygen atoms has atomic mass of
3 × 16 = 48 u
So, two atoms of aluminum must have anatomic mass of
102 u− 48 u= 54 u
Thus, one atom of aluminum has atomic mass of
54 u
2 =^27 u
Avogadro’s Number
In 1811, Amedeo Avogadro (1776-1856), in the Figure14.1, published a paper hypothesizing that equal volumes
of different gases gas at equal pressure and temperature would have an equal number of molecules. Today we know
that a volume of 22.4 liters of an ideal gas at standard atmospheric pressure and 20°C contains one mole of gas.
The number of molecules in one mole was not determined until the early 20th century. The number is known today
asAvogadro’s NumberNA= 6. 022 × 1023 and is defined as one mole.
FIGURE 14.1
Amedeo Avogadro