Molar Mass

Molar mass is the mass in grams of 1 mole of a substance .  It can be calculated by summing all the masses of all the atoms present in a compound.  For an element, the molar mass is equal to the atomic weight.

Mass of 1 mol of C  =  12.01 g
Mass of 1 mol of CH₄ = 16.04 g

The molar mass in grams per mole of any substance is numerically equal its formula weight in atomic mass unit.

1 mole of NaCl = 58 g/mol, molar mass
                         =  58 amu, formula weight

1 mole of CO₂ =  44 g/mol, molar mass
                         =  44 amu, fomula weight

1 mole of Al  =  27 g/mol, molar mass
                      =  27 amu, formula weight

Calculating Molar Mass

Sample Problem 1

What is the molar mass of glucose, C₆H₁₂O₆?

Solution:

Sample Problem 2
Calculate the molar mass of  Ca(NO₃)₂.

Sample Problem 3
Calculate the molar mass of CaCO₃

Sample Problem 4
Calculate the molar mass of SO₂.

Sample Problem 5

Calculate the molar mass of caffeine, C₈H₁₀N₄O₂.

Interconverting Masses and Moles

Since you know already how to calculate the molar mass of different substances, you are now ready to solve for mole and mass using molar mass of the compound.

You can use the formulas below:

No. of moles  =  mass ÷ molar mass

mass =  no. of moles x molar mass

or you can use the Factor Label Method of Calculating Problems.


Sample Problem 1
Calculate the number of moles of glucose (C₆H₁₂O₆) in 5.380 g of glucose.

Solution:
From the calculated molar mass of glucose above  is 180 g/mol.


Sample Problem 2
Calculate the mass in grams of 0.433 mol of calcium nitrate, Ca(NO₃)₂.

Solution:
The calculated molar mass of calcium nitrate is 164 g/mol.



Sample Problem 3

What is the mass in grams of a) 6.33 mol of NaHCO₃  b) 3.0 x 10^-5 mol of H₂SO₄.

Solution :
a.)  Calculating the molar mass of NaHCO₃

b.  Calculating the molar mass of  H₂SO₄