CALCULATIONS BASED ON FORMULAE

7.5 - Calculations involving Avogadro's number

7.5.3 - Mass in grams to number of particles conversion

Whenever you want to convert quantities from one unit to another, you need to use the appropriate conversion factor. The conversion factor must have units of the two quantities involved.

To convert between mass in grams and number of particles^* it will require two steps as there is not a single quantity that relates these two units.

Step 1:	Convert the mass in grams to moles. This step is explained in detail in section 7.5.1.
Step 2:	Convert the calculated quantity from step 1 in moles to the number of particles. This step is explained in detail in section 7.5.2.

^* particles can be protons, electrons, atoms, ions, molecules, etc ...

For example:

How many oxygen atoms are there in 5.0 grams of Na₂CO₃?

These are the steps that I would take to answer the question.

Step 1: How many moles of Na₂CO₃ are there in 5.0 grams of Na₂CO₃?
Convert the mass (in grams) to moles (see section 7.5.1) .

Step 2: In this many moles of Na₂CO₃, as calculated in step 1, how many moles of oxygen atoms are there?
Recall our previous analysis of Na₂CO₃. See section 5.9.1 for the number of particles conversion.

Step 3: In this many moles of oxygen, as calculated in step 2, how many oxygen atoms are there?
Convert the moles of atoms to number of atoms (see section 7.5.2) .

Section 8.2
Calculation of Moles of Units. Avogadro's Number (N) ..p189

Back

Next