If I want to visit the town of Manteo, North Carolina, out on the coast, I will need a map of how to get there. I may have a printed map or I may download directions from the internet, but I need something to get me going in the right direction. Chemistry road maps serve the same purpose. How do I handle a certain type of calculation? There is a process and a set of directions to help.

Previously, we saw how the conversions between mass and number of particles required two steps, with moles as the intermediate. This concept can now be extended to also include gas volume at STP. The resulting diagram is referred to as a mole road map (see figure below).

Figure 10.9.1: The mole road map shows the conversion factors needed to interconvert between mass, number of particles, and volume of a gas.

The mole is at the center of any calculation involving amount of a substance. The sample problem below is one of many different problems that can be solved using the mole road map.

Example 10.9.1

What is the volume of $$79.3 \: \text{g}$$ of neon gas at STP?

Solution:

Step 1: List the known quantities and plan the problem.

Known

• $$\ce{Ne} = 20.18 \: \text{g/mol}$$
• $$1 \: \text{mol} = 22.4 \: \text{L}$$

Unknown

• Volume $$= ? \: \text{L}$$

The conversion factors will be grams $$\rightarrow$$ moles $$\rightarrow$$ gas volume.

Step 2: Calculate.

$79.3 \: \text{g} \: \ce{Ne} \times \frac{1 \: \text{mol} \: \ce{Ne}}{20.18 \: \text{g} \: \ce{Ne}} \times \frac{22.4 \: \text{L} \: \ce{Ne}}{1 \: \text{mol} \: \ce{Ne}} = 88.0 \: \text{L} \: \ce{Ne}$