Question

The 54.9-g sample of the compound X2O7 contains 33.6 g of oxygen atoms. What is the molar mass of element X?

Answer 1

Mass of X₂O₇ = 54,9g

2x + 33,6g = 54,9g
2x = 54,9g - 33,6g
2x = 21,3g  | :2
x = 10,65g/mol

Answer 2

Answer: The molar mass of element X is 35.5 g/mol

Explanation:

We are given:

A chemical compound having formula $X_2O_7$

1 mole of this compound contains 2 moles of element X and 7 moles of oxygen

Mass of oxygen atoms = 33.6 grams

Mass of sample = 54.9 g

Mass of X atoms = (54.9 - 33.6)g = 21.3 g

We know that:

Molar mass of oxygen = 16 g/mol

To calculate the molar mass of element X, we use unitary method:

33.6 g of oxygen combines with 21.3 g of element X.

So, $(7\times 16)=112g$ of oxygen atom will combine with $\frac{21.3}{33.6}\times 112=71g$ of element X

From the given formula, 2 moles of element X are present.

So, molar mass of element X = $\frac{\text{Total mass of X}}{\text{Number of atoms in the compound}}=\frac{71g}{2mol}=35.5g/mol$

Hence, the molar mass of element X is 35.5 g/mol