Question

$10$ g of a certain compound having molecular formula $X_4{O}_6$ has $5.72$ g of X.

What is the atomic mass of X?

• A. 32 amu
• B. 37 amu
• C. 42 amu
• D. 98 amu

Answer 1

The correct option is A 32 amu

Let the atomic mass of $X$ be $x$ amu.

The molar mass of $X_4{O}_6$ will be $4x+96$ amu.

10 g of the compound will contain $\frac{10}{4x+96}$ moles

This corresponds to $\frac{4\times 10}{4x+96}$ moles of X or $\frac{40x}{4x+96}$ g of X which is equal to 5.72 g.

Thus, $\frac{40x}{4x+96}=5.72$

$6.99x=4x+96$

$2.99x=96$

$x=32amu$

So, the atomic mass of $X$ is $32$amu.

Hence, the correct option is $A$