Question

The molecular formula of certain compound has $X_4O_6$. If 10 g of $X_4O_6$ has 5.72 g $X$, then the atomic mass of X is

• A. 42
• B. 30
• C. 24
• D. 32

Answer 1

Answer: (D)

32

Answer 2

Here's how to determine the atomic mass of X:

1. Calculate the mass of oxygen:

   Mass of oxygen = Total mass - Mass of X = $10 \text{ g} - 5.72 \text{ g} = 4.28 \text{ g}$

2. Calculate moles of oxygen:

   Moles of oxygen ($n_O$) = $\frac{\text{Mass of oxygen}}{\text{Atomic mass of oxygen}} = \frac{4.28 \text{ g}}{16 \text{ g/mol}} = 0.2675 \text{ mol}$

3. Determine the mole ratio of X to O:

   From the formula $X_4O_6$, the ratio of X to O is 4:6, which simplifies to 2:3.

4. Calculate moles of X:

   Since $\frac{n_X}{n_O} = \frac{2}{3}$, then $n_X = \frac{2}{3} \times n_O = \frac{2}{3} \times 0.2675 \text{ mol} = 0.1783 \text{ mol}$

5. Calculate the atomic mass of X:

   Atomic mass of X ($M_X$) = $\frac{\text{Mass of X}}{\text{Moles of X}} = \frac{5.72 \text{ g}}{0.1783 \text{ mol}} \approx 32.08 \text{ g/mol}$

Therefore, the atomic mass of X is approximately 32.