We’re being asked to** ****determine the number of atoms of zinc in a fitting** containing **37.0 % by mass Zn**.

We know that the fitting is a common brass alloy composed of copper, Cu and Zinc, Zn.

And to do that we're going to do the following steps:

*Step 1: Solve for mass of the common brass fitting (solution) using the volume and *

*density of the fitting.*

**volume solution (density) → mass solution**

*Step 2: Solve for mass of Zinc using the mass percent formula shown below:*

$\overline{){\mathbf{mass}}{\mathbf{}}{\mathbf{percent}}{\mathbf{=}}\frac{\mathbf{mass}\mathbf{}\mathbf{component}}{\mathbf{total}\mathbf{}\mathbf{mass}}{\mathbf{\times}}{\mathbf{100}}}$

Since we are dealing with an **alloy (solid solution)**, we can rewrite the equation as:

$\overline{){\mathbf{\%}}{\mathbf{}}{\mathbf{mass}}{\mathbf{=}}\frac{\mathbf{mass}\mathbf{}\mathbf{solute}}{\mathbf{mass}\mathbf{}\mathbf{solution}}{\mathbf{\times}}{\mathbf{100}}}$

*Step 3: Solve for moles of Zn in fitting and # of atoms of Zn using Avogadro's number*

Common brass is a copper and zinc alloy containing 37.0% zinc by mass and having a density of 8.48 g/cm^{3}. A fitting composed of common brass has a total volume of 120.5 cm^{3} .

How many atoms of zinc does the fitting contain?