What is the molar mass of a ficticious element X if 109.9 g of X are required to react with 27.5 g of O2 to produce X2O3?

95.91 g/mol

Explanation:

You need to create an equation using the given information.

X  +  O₂  ⇒  X₂O₃

You now have to balance the equation

4 X  +  3 O₂  ⇒  2 X₂O₃

Using this information, you can solve for the molar mass of X.  First, convert grams of O₂ to moles.  The molar mass is 32.00 g/mol.

(27.5 g)/(32.00 g/mol) = 0.8594 mol O₂

Next, use the mole ratio in the chemical equation to convert moles of O₂ to moles of X.  

0.8594 mol O₂ × (4 mol X/3 mol O₂) = 1.146 mol X

Now that you have the moles, divide the given grams of X by the calculated value of moles.

(109.9 g)/(1.146 mol) = 95.91 g/mol

The molar mass of element X is 95.91 g/mol.

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