CHAPTER 72 How to find the molar mass of an element The molar mass of any substance is the mass in grams of one mole of the substance It is expressed as gramsmole g mol The molar mass of ID: 580047
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Slide1
MOLAR MASS
CHAPTER 7-2Slide2
How to find the molar mass of an element
The
molar mass
of any substance is the mass (in grams) of one mole of the substance.
It is expressed as grams/mole (
g/
mol
).
The molar mass of
elements
is found by looking at the average atomic mass of the element on the periodic table.Slide3
Sample Problems
Find the molar mass of the following elements:
C = 12 g C / 1
mol
C
Fe = 56 g Fe / 1
mol
Fe
Ca = 40 g Ca / 1
mol
CaSlide4
How to find the molar mass of a compound
The molar mass of
compounds
, we need to find the molar mass from the chemical formula of the compound.
The molar mass of a compound can be calculated by adding the average atomic masses (in g/
mol
) of the atoms in the compound.
Molar mass serves as a bridge between the mass of a material and the number of
moles
since it is not possible to measure the number of moles directly.Slide5
Sample Problem
Find the molar mass of H
2
O
H = 2 x 1.0 = 2
O = 1 x 16 = 16
18
Molar mass of H
2
O is 18 g/mol . It is a conversion unit and it can be written as 18 g H2O = 1 mol H2OSlide6
Converting grams to moles and moles to grams
molar
mass of N
2
O
3
= 76 g/
mol
Molar mass is used to convert between grams and moles of substances.
Sample Problem
How many grams are in 9.45
mol of N2O3
76 g
N2O3 9.45 mol N2O3 x = 718 g N2O3 1 mol N2O3