# A sample of a pure substance with a mass of 0.963g contains 4.84x1-^-3 moles. What is the formula weight of the substance comprising the sample?

Jul 15, 2017

$200.$ $\text{amu}$

#### Explanation:

We're asked to calculate the formula weight of a pure substance, knowing that $4.81 \times {10}^{-} 3$ $\text{mol}$ has a mass of $0.963$ $\text{g}$.

To calculate the formula weight (relative atomic mass, atomic weight, etc.; they mean the same thing), we'll first calculate the *molar mass of the substance:

$\text{molar mass" = "mass"/"mol}$ $= \left(0.963 \textcolor{w h i t e}{l} \text{g")/(4.81xx10^-3color(white)(l)"mol}\right)$

= color(red)(200. color(red)("g/mol"

Remember the important conecpt of the mole:

The mass in grams of one mole of a substance is equal to the mass in atomic mass units of one individual unit of that substance.

Therefore, we have

overbrace(200. color(white)(l)"g/mol")^"mass of one mole" = overbrace(color(blue)(200. color(white)(l)"amu"))^"mass of one unit"