What is the molar mass of magnesium oxide? I want the answer not to be round and to be used by this periodic chart
Molar mass is the mass of one mole of a compound. One mole is 6.02x10^23 molecules of that compound.
The formula for magnesium oxide is MgO. This means every molecule of magnesium oxide contains one magnesium atom and one oxygen atom. In order to find the molar mass of a compound, you must sum the individual molar masses of the atoms which form that compound.
The molar mass of an element is the atomic weight of that element. Using the table you provided, we find the molar masses of Mg and O are 24.305 grams/mol and 15.999 grams/mol, respectively.
So the molar mass of magnesium oxide is (24.305 + 15.999) = 40.304 grams/mole.
Now, with regards to rounding, 40.304 is a correct answer with respect to significant digits.