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?

1 Answer
Jul 15, 2017

Answer:

#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"#