*Mole Fraction (X)** relates the moles of solute and solvent within a solution:*

$\overline{){\mathit{m}}{\mathit{o}}{\mathit{l}}{\mathit{e}}{\mathbf{}}{\mathit{f}}{\mathit{r}}{\mathit{a}}{\mathit{c}}{\mathit{t}}{\mathit{i}}{\mathit{o}}{\mathit{n}}{\mathbf{}}{\mathbf{\left(}}{\mathit{X}}{\mathbf{\right)}}{\mathbf{=}}\frac{\mathbf{m}\mathbf{o}\mathbf{l}\mathbf{e}\mathbf{}\mathbf{o}\mathbf{f}\mathbf{}\mathbf{s}\mathbf{o}\mathbf{l}\mathbf{u}\mathbf{t}\mathbf{e}}{\mathbf{m}\mathbf{o}\mathbf{l}\mathbf{e}\mathbf{}\mathbf{o}\mathbf{f}\mathbf{}\mathbf{s}\mathbf{o}\mathbf{l}\mathbf{u}\mathbf{t}\mathbf{i}\mathbf{o}\mathbf{n}}}$

**Step 1: Calculate the mole of solute **

•** Recall molarity (M): **

$\mathbf{molarity}\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{moles}\mathbf{}\mathbf{solute}}{\mathbf{L}\mathbf{\hspace{0.17em}}\mathbf{solution}}\phantom{\rule{0ex}{0ex}}\mathbf{2}\mathbf{.}\mathbf{800}\mathbf{}\mathbf{\times}\mathbf{}{\mathbf{10}}^{\mathbf{-}\mathbf{2}}\mathbf{}\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{mole}\mathbf{}\mathbf{NaCl}}{\mathbf{1}\mathbf{}\mathbf{L}}\phantom{\rule{0ex}{0ex}}\mathbf{moles}\mathbf{}\mathbf{NaCl}\mathbf{}\mathbf{=}\mathbf{}\mathbf{0}\mathbf{.}\mathbf{0280}\mathbf{}\mathbf{mol}$

A 2.800x10^{-2} M solution of NaCl in water is at 20.0° C. The sample was created by dissolving a sample of NaCl in water and then bringing the volume up to 1.000 L. It was determined that the volume of water needed to do this was 999.2 mL. The density of water at 20.0° C is 0.9982 g/mL.

Calculate the mole fraction of salt in this solution.

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