### All SAT II Chemistry Resources

## Example Questions

### Example Question #1 : Other Stoichiometric Calculations

What is the mass percent of chromium in ?

Use the values in the following table for the atomic masses of the elements shown.

**Possible Answers:**

**Correct answer:**

In order to find the mass percent of a certain atom in a particular molecule, you must know the mass the atom contributes to the molecule and the total mass of the molecule. In this case we calculate the mass percent using the equation

Calculating the mass of in the molecule is done by multiplying the atomic mass of a atom by the number of atoms of that element present in the molecule. There are six atoms in the presented molecule. We can tell this because has a subscript of 2 and is contained in a set of parentheses that has a subscript of 3. This tells us that there are three sets of two atoms in each of the molecules. The atomic mass of a atom is given as 52.00 amu, so we can multiply:

Now we need to calculate the total atomic mass of the molecule. We can do this by identifying the atomic mass of each element in the molecule, multiplying it by the number of that type of atom in the molecule, and summing the results together.

We then plug in the values into equation to find the mass percent.