Common brass is a copper and zinc alloy containing 37.0% zinc by mass and having a density of 8.48 g/cm3. a fitting composed of common brass has a total volume of 112.5cm^3. how many atoms of copper and zinc does the fitting contain?

First, determine the mass of the alloy by multiplying the density and volume.
                            m = (8.48 g/cm³)(112.5 cm³) = 954 g
The mass of zinc in this alloy is,
                                    (954 g)(0.37) = 352.98 g
        mass of copper,
                                      954 g - 352.98 g = 601.02 g
Then, calculate the number of moles of zinc and copper present by dividing its mass with the molar mass. The molar mass of zinc is 65.38 g/mol and that of copper is 63.55 g/mol
                             n (zinc) = 352.98 g / (65.38 g/mol) = 5.40 moles
                             n (copper) = 601.02 g / (63.55 g/mol) = 9.46 moles
The number of atoms of copper and zinc are determined by multiplying the number of moles with the Avogadro's number and the answers are,
                          atoms (zinc) = 3.25 x 10^24 atoms
                          atoms (copper) = 5.70 x 10^24 atoms