An oxide of an element has the formula $X_{2} O_{7}$ $"X"_2"O"_7$ and contains 50.45 % oxygen. What is the atomic mass of the element?

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Answer 1 · 2014-10-25T19:28:26

The atomic mass of the element is 55.00 u.

The formula of the oxide is X₂O₇.

Assume 100 g of the oxide.

Then you have 50.45 g of O and 49.55 g of X.

Moles of O = 50.45 g O × $\frac{1 mol O}{16.00 g O}$ $"1 mol O"/"16.00 g O"$ = 3.153 mol O

Moles of X = 3.153 mol O × $\frac{2 mol X}{7 mol O}$ $"2 mol X"/"7 mol O"$ = 0.9009 mol X

Molar mass of X = $\frac{49.55 g}{0.9009 mol}$ $"49.55 g"/"0.9009 mol"$ = 55.00 g/mol

The atomic mass of X is 55.00 u.

An oxide of an element has the formula X2O7"X"_2"O"_7 and contains 50.45 % oxygen. What is the atomic mass of the element?