The chemical equation below shows the burning of magnesium (Mg) with oxygen (O2) to form magnesium oxide (MgO). 2Mg + O2 Right arrow. 2MgO The molar mass of O2 is 32.0 g/mol. What mass, in grams, of O2 is required to react completely with 4.00 mol of Mg? 2.00 64.0 128 256

64.0

Explanation:

2Mg+O2 ---> 2MgO

use dimentional analysis to find the amount of moles of O2 needed first

4.00molMg x 1.00mol O2/ 2.00 mol Mg=. 2.00 mol O2

using the coefficients you can see the mole ratio for O2:Mg the mole ratio is 1:2 which is why there is 1 mole on the top for 2 moles on the bottom. The Mg would cancel and multiply 4 by 1 then divide by 2, or multipy 4 by 1/2

Now that you have the moles of O2 you use the molar mass to find the grams in 2 moles of O2

2.00 mol O2 x 32.0g/1.00 mol = 64.0 g

multiply 2 by 32

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