Calculate the number of molecules in 1.058 mole (or gram) of H 2 O Calculate the number of atoms in 0.750 mole (or gram) of Fe These problems use the reverse technique of the above. Once again, replacing mole with gram adds one step to the procedure. Here is a graphic of the procedure steps. You cannot directly convert grams to atoms. First you must covert your grams to moles, then you can take the moles and covert to atoms. If you take your 878 grams of fluorine and then look at the.
Refer to the periodic table of elements and find the atomic weight for the substance you are working with, rounding to the appropriate number of significant digits. In this case, carbon has an atomic weight of 12.0 atomic mass units (amu).
The molar mass (in grams) of any substance is always numerically equal to its formula weight (in amu), so for carbon, there are 12.0 grams (g) in one mole of carbon. Write this as a fraction to the right of Step 2, again multiplying. Also, put an equal sign to the far right. It should look like this.