Moles to Grams… Grams to Moles

After the excitement of MOLE DAY, it’s time to actually start using those friendly moles to our benefit. Today, we’ll be finishing the third part of our Mole lab with Cu/Fe. As a part of that lab, we’ll need to calculate how many moles of Cu/Fe were produced using the amount of grams of each.

To calculate grams to moles we use the FACTOR LABEL method. Let me show you what I mean…

Lets say you weighed your sample and have 105.5 g Cu atoms (Its important to label your values this way for future use; we’ll always add the element and “atoms” after the unit) and we want to know how many moles that is. well what do we know…

105.5 g Cu atoms   ->   ??? mol g Cu atoms

Well… lets think about this. Do we know how many grams are in 1 mol Cu atoms so we have something to compare this to??? Let’s look at our handy-dandy periodic table; find Cu; the atomic mass listed there is equal to the weight of 1 mol Cu atoms!

1 mol Cu atoms
63.5 g Cu atoms

So lets put this value into our formula and see if we can make this work…

105.5 g Cu atoms   x  1 mol Cu atoms
1                                  63.5 g Cu atoms

We can cross out the “g Cu Atoms” units so the only unit remaining is “mol Cu atoms“. So…

105.5 x 1 mol Cu atoms       = 1.66 mol Cu atoms

___________Easy! When you go from grams to moles you DIVIDE BY THE ATOMIC MASS!_______________
But, what if I want to go from moles to grams??? EASY!!! MULTIPLY BY THE ATOMIC MASS!
What is the weight of 2.5 moles of Carbon atoms?

2.5 mol C atoms x 12.0 g C atoms  30.o g C atoms
1                           1 mol C atoms

Since, 1 mole of any element = atomic weight of that element, you can flip the equation to work for you! Since we have moles on the top left of the formula, we want moles on the bottom right so they can cancel out!

Your homework for tonight is to finish the first 10 problems (the front side) of the Grams to Moles Conversions Worksheet (found on semester 1 Docs).