Question

How many total atoms are in 0.670 g of p2o5?

Answer 1

The molecular formula for compound is  $P_{2}O_{5}$ mass of compound is 0.670 g.

To calculate number of atoms first calculate number of moles in the compound as follows:

$n=\frac{m}{M}$

Molar mass of  $P_{2}O_{5}$ is 283.886 g/mol, thus,

$n=\frac{0.670 g}{283.886 g/mol}=0.00236 mol$

Thus, number of mole of $P_{2}O_{5}$ is 0.00236 mol.

From the molecular formula 1 mole of $P_{2}O_{5}$ has 2 mol of P (phosphorus) and 5 mol of O (oxygen).

Thus, number of moles of P and O in 0.00236 mol of $P_{2}O_{5}$ will be:

$n_{P}=2\times 0.00236 mol=0.00472 mol$

Similarly,

$n_{O}=5\times 0.00236 mol=0.0118 mol$

Now, in 1 mol of an element there are $6.023\times 10^{23}$ atoms.

Number of atoms of P will be:

$N_{P}=0.00472\times 6.023\times 10^{23}=2.84\times 10^{21}atoms$

Similarly, number of atoms of O will be:

$N_{O}=0.0118\times 6.023\times 10^{23}=7.11\times 10^{21}atoms$

Total number of atoms will be sum of number of atoms of P and O:

$N_{Total}=N_{P}+N_{O}=2.84\times 10^{21}+7.11\times 10^{21}=9.95\times 10^{21} atoms$

Therefore, total number of atoms in $P_{2}O_{5}$ will be $9.95\times 10^{21} atoms$.