Question

How many total atoms are in .660 g of `P_2O_5`?

Answer 1

`14 xx 10 ^21` atoms

Explanation:

Let us first calculate the number of moles of Phosphorous (`V`) Pentoxide i.e. `P_2O_5`

mass of `P_2` `O_5` = `0.660` `g`

molar mass of `P_2` `O_5` = `142` `g` `mol^-1`

`"number of moles of"` `P_2` `O_5` = `"mass" /"molar mass"`

`n = 0.660 / 142` `g` `mol^-1`

`n = 0.0046` `mol` of `P_2` `O_5`

one mole of `P_2` `O_5` has 5 moles of Oxygen atoms.

using this we can write two conversion factors

1 mol `P_2` `O_5`/ 5 mol Oxygen or 5 mol Oxygen / 1 mol `P_2` `O_5`

using conversion factor

`0.0046` `mol` of `P_2` `O_5` x `[ (5 " mol " O_2 ) /( 1 " mol " P_2O_5)]`

= `0.023` `mol` of Oxygen

`0.023` `mol xx 6.02 xx 10 ^23` `"atom"` / `mol`

= `14 xx 10 ^21` `"atoms"`