Question

If we have a $CuS{O}_4.5H_{2}O$ sample and it contains a total of 1116 oxygen atoms, find the number of formula units of $CuS{O}_4.5H_{2}O$ present in the sample.

• A. 124
• B. $9N_A$
• C. $0.124N_A$
• D. 279

Answer 1

The correct option is A 124

One formula unit of $CuS{O}_4.5H_{2}O$ has 9 oxygen atoms.
So, 1116 oxygen atoms will be present in
$=\frac{1116}{9}$ formula units of $CuS{O}_4.5H_{2}O$
$=$ 124 formula units of $CuS{O}_4.5H_{2}O$