Question

calculate the number of atoms of o in 7.23 moles of fe(no₃)₃.

Explanation:

Step1: Determine O atoms per formula unit

In one formula - unit of $Fe(NO_3)_3$, there are 9 oxygen atoms (3 nitrate ions $NO_3^-$ and each $NO_3^-$ has 3 O atoms: $3\times3 = 9$).

Step2: Calculate moles of O atoms

If there are 7.23 moles of $Fe(NO_3)_3$, then the number of moles of O atoms is $n = 7.23\times9=65.07$ moles.

Step3: Use Avogadro's number

Avogadro's number $N_A=6.022\times 10^{23}$ atoms/mol. The number of O - atoms $N=n\times N_A$. So $N = 65.07\times6.022\times 10^{23}$ atoms.
$N=3.9285154\times 10^{25}$ atoms.

Answer:

$3.93\times 10^{25}$ atoms