Problem: A 67.2 g sample of a gold and palladium alloy contains 3.20×1023 atoms .What is the mass percentage of the gold in the alloy?

$\boxed{\mathbf{mass}\mathbf{ }\mathbf{percent}\mathbf{ }\mathbf{gold}\mathbf{=}\frac{\mathbf{mass}\mathbf{ }\mathbf{gold}}{\mathbf{mass}\mathbf{ }\mathbf{alloy}}\mathbf{\times }\mathbf{100}}$

Avogadro’s number = 6.022 x 10²³ entities

                                      entities = atoms, ions, molecules, particles, formula units

If n = moles of Au then m = moles of Pd

$$\begin{gathered} \mathbf{mass}\mathbf{ }\mathbf{alloy}\mathbf{ }\mathbf{=}\mathbf{67}\mathbf{.}\mathbf{2}\mathbf{=}\mathbf{ }\mathbf{n}\mathbf{(}\mathbf{196}\mathbf{.}\mathbf{97}\mathbf{ }\frac{\mathbf{g}}{\mathbf{mol}}\mathbf{Au}\mathbf{)}\mathbf{+}\mathbf{m}\mathbf{(}\mathbf{106}\mathbf{.}\mathbf{42}\frac{\mathbf{g}}{\mathbf{mol}}\mathbf{Pd}\mathbf{)} \\ \mathbf{total}\mathbf{ }\mathbf{\#}\mathbf{ }\mathbf{of}\mathbf{ }\mathbf{atoms}\mathbf{ }\mathbf{=}\mathbf{3}\mathbf{.}\mathbf{20}\mathbf{\times }{\mathbf{10}}^{\mathbf{23}}\mathbf{=}\mathbf{n}\mathbf{(}\mathbf{6}\mathbf{.}\mathbf{022}\mathbf{\times }{\mathbf{10}}^{\mathbf{23}}\mathbf{ }\mathbf{atoms}\mathbf{ }\mathbf{Au}\mathbf{)}\mathbf{+}\mathbf{m}\mathbf{(}\mathbf{6}\mathbf{.}\mathbf{022}\mathbf{\times }{\mathbf{10}}^{\mathbf{23}}\mathbf{ }\mathbf{atoms}\mathbf{ }\mathbf{Pd}\mathbf{)} \end{gathered}$$