Molar Mass
Since the particles are a group of
atoms chemically joined together the final mass for these molecules known from
the masses of their atoms i.e., we use relative mass to compare various molecules
in terms of mass. Meaning that:-
Molar mass of matter =Total relativistic
masses of atoms which make up matter
Molar mass is the mass of 1 mole of
a compound in gram unit. (Molar mass used to be called as molecular mass
formerly.)
For example, if we want to calculate
the molar mass of methane gas (CH4) or if we ask what is the mass of
1 mole of methane gas, as each methane molecule has 1 C and 4 H atoms, 1 mole of
methane molecule contains 1 mole of C atom and 4 moles of H atoms. According to
this, we can calculate the mass of 1 mole of methane gas as follows:
· Mass of 1 mole of C = 1 × 12 = 12 g/mol
· Mass of 4 moles of H = 4 × 1= 4 g/mol
· Mass of 1 mole of CH4 = 16 g/mol
In the same manner, we can calculate
molar mass of H2SO4 acid.
· Mass of 2 moles of H = 2 × 1= 2 g/mol
· Mass of 1 mole of S = 1 × 32 = 32 g/mol
· Mass of 4 moles of O = 4 × 16 = 64 g/mol
· Mass of 1 mole of H2SO4= 98 g/mol
If 16g of methane gas makes up 1 mole
of CH4 and 98 g of sulfuric acid makes up 1 mole of H2SO4,
logically we can call those masses as molar mass. As we understand from previous
calculations we have made, in chemistry, all atoms and molecules are bound with
the following:
1. Atomic mass and molar mass
2. Mole
3. Avogadro’s number
Avogadro’s number or Avogadro’s
constant is the number of atoms in 1 mole of an element or number of molecules
in 1 mole of a molecule. It is shown with NA. Previously, we have mentioned
that atoms, molecules or ions as many as Avogadro’s number are called as a
mole.
Example 1
Find the molar mass for the
following compounds:
a. Aqueous sodium sulfate Na2SO4.7H2O
b. Juglone C10H6O3
c. Sulfur dioxide SO2
Solution:
Example 2
Find out the mole numbers of the
following compounds.
a)9.6 g of SO2
b) 85 g of NH3
Solution:
a) Molar mass of SO2:
b) Molar mass of NH3:
Example 3
Calculate the mass of 0.7 mol of
manganese dioxide (MnO2).
Solution:
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