# Question 038ae

Jan 22, 2018

54.41 grams.

#### Explanation:

In general, the mass of a substance can be found from the number of moles by:

$\text{mass" = "moles" xx "molar mass}$

For $\text{MgO}$, the molar mass of the molecule can be found by adding up the molar masses of its constituent atoms. That is, (values taken from Google)

"molar mass"("MgO") = "molar mass"("Mg") + "molar mass"("O")#

$= \text{24.31 g.mol" + "16.00 g/mol}$

$\text{= 40.31 g/mol}$

Or, the molar mass of $\text{MgO}$ might often be given to you. Either way,

$\text{mass" = "moles" xx "molar mass}$

$= \text{1.350 moles" xx "40.31 g/mol}$

$\text{= 54.41 g}$ (rounded)