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?

Md Ariful Islam

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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 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

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

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