# Coal is not a pure chemical compound, but its elemental composition can be approximated by the formula #C_135H_96NO_9S#. What is the approximate percentage by mass of sulfur in coal?

##### 1 Answer

1.8%

#### Explanation:

**1. Use the formula:**

**% by mass = (mass of part / mass of whole) x 100**

*What to we need to know to use this formula?*

We need the mass of the part (**sulfur**) and the mass of the whole (**coal**).

*What are we solving for?*

We are solving for % by mass of sulfur in coal.

**2. To find the mass of the part (sulfur):**

Look at the molecular formula and see **how many sulfur atoms** there are.

There is just 1 sulfur (S) atom in the formula.

Since the atomic mass of sulfur is approximately 32.1 and there's only one sulfur atom here, **the mass of the part is 32.1**.

*You can find information about atomic mass for any element on a periodic table.*

**3. To find the mass of the whole (coal):**

First, count up the number of atoms of each element present in the formula.

C: 135 atoms

H: 96 atoms

N: 1 atom

O: 1 atom

S: 1 atom

Now multiply the # of atoms number by the atomic mass.

C: 135 atoms x 12.0

H: 96 atoms x 1.0

N: 1 atom x 14.0

O: 1 atom x 16.0

S: 1 atom x 32.1

C: 1620

H: 96

N: 14

O: 16

S: 32.1

Finally, add up your numbers to find the mass of the whole.

**1778.1 is the mass of the part.**

**4. Plug your answers into the formula and solve!**

% by mass

% by mass

% by mass

The approx. % by mass of sulfur in coal is 1.8%.