Question

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?

Answer 1

`200.` `"amu"`

Explanation:

We're asked to calculate the formula weight of a pure substance, knowing that `4.81xx10^-3` `"mol"` has a mass of `0.963` `"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:

`"molar mass" = "mass"/"mol"` `= (0.963color(white)(l)"g")/(4.81xx10^-3color(white)(l)"mol")`

`= 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"`