Moles to Grams to Moles

General Chemistry Index

Where are we going with this? This page will give the ability to demonstrate an understanding of the law of conservation of mass through the use of particle diagrams and mathematical models.

Moles to Grams to Moles
Moles to grams you multiply. Grams to moles divide.

This is so important to understand, I made a cringy video. Really.

https://youtu.be/84MUkdZyxUQ

Did you catch that? 

Moles to grams you multiply. Grams to moles, you divide!

Divide? Multiply? What??? Multiply what!

How Does This Thing Work?

Okay, back to that periodic table… Back to that atomic number… 

The atomic number gives the mass in grams of one mole of atoms of the element.

If you have a molecule of atoms, you can find the molecular mass by adding up all of the atomic masses of all of the atoms in the molecule. Really.

If you know the molecular mass of a substance, you know how much one mole of that substance weighs in grams. 

Ah ha!!!

Moles to grams you multiply. Grams to moles, you divide!

 Moles = Grams ÷ Molar mass

Grams = Moles X Molar mass

EXAMPLES:

Water is H20.

Two atoms of Hydrogen. One atom of oxygen.  Thus, adding up the masses of the atoms, we find that one molecule of water has the molecular mass of 31.998 grams / mole.

Suppose you have 5.5 grams of water… How many moles do you have?

Moles = Grams ÷ Molar mass 

Moles = 5.5 ÷ 31.998

Moles = 0.17198

Suppose you have .5 moles of water… How many grams do you have?

Grams = Moles X Molar mass

Grams = .5 X 31.998

Grams = 15.999

Moles to grams you multiply. Grams to moles, you divide!