Question

What is the percent composition by mass of oxygen in magnesium oxide.

Answer 1

Step-by-step explanation:

Magnesium Oxide has a formula of MgO.

Magnesium has a molar mass of 24.30g/mol and Oxygen has a molar mass of 15.99g/mol.

From this, we can say we are assuming a 1 mole sample of magnesium oxide, as the stoichiometric coefficients will always be the same, as will the ratio of oxygen to magnesium.

From this,

`15.99g/mol *1 mol MgO = 15.99 gOxygen\\24.30g/mol *1molMgO=24.30gMagnesium\\Oxygen mass percent = 15.99/(15.99+24.30) = .396`

The Magnesium equation will be the same but a different numerator. Notice, if there were different coefficients on the elements, you would have to multiply by the stoich coefficient.