Question

calculate the number of phosphorus atoms in a 60.0 g sample of diphosphorus pentoxide (p₂o₅). be sure your answer has a unit symbol if necessary, and round it to 3 significant digits.

Explanation:

Step1: Calculate molar mass of $P_2O_5$

The molar mass of $P$ is approximately $30.97\ g/mol$ and of $O$ is approximately $16.00\ g/mol$. For $P_2O_5$, $M = 2\times30.97+5\times16.00= 141.94\ g/mol$.

Step2: Calculate moles of $P_2O_5$

$n=\frac{m}{M}$, where $m = 60.0\ g$ and $M = 141.94\ g/mol$. So $n=\frac{60.0}{141.94}\ mol\approx0.4227\ mol$.

Step3: Determine moles of $P$ atoms

In one - mole of $P_2O_5$, there are 2 moles of $P$ atoms. So moles of $P$ atoms, $n_P=2\times n_{P_2O_5}=2\times0.4227\ mol = 0.8454\ mol$.

Step4: Calculate number of $P$ atoms

Using Avogadro's number $N_A = 6.022\times10^{23}\ atoms/mol$, the number of $P$ atoms $N=n_P\times N_A=0.8454\times6.022\times10^{23}\ atoms\approx5.09\times 10^{23}\ atoms$.

Answer:

$5.09\times 10^{23}\ atoms$