Question

How many moles of chlorine are present in 2.47 g of phosphorus pentachloride?

Answer 1

`0.0592` moles of `Cl`.

Explanation:

In this type of question it is important to define whether you are looking for a "mole" of atomic chlorine (one atom - `Cl`) or a mole of the normal form of the diatomic gas chlorine, `Cl_2`.

For this problem I will stick with the pure atomic definition, that is, a single chlorine atom. The results can be halved to obtain the gas molecule version, if you like.

`PCl_5` has 5 moles of Cl per compound mole. One mole of `PCl_5` has a molecular weight of `(208.5g)/"mole"`.

Thus, `2.47g` is `2.47/208.5 = 0.01185` moles of `PCl_5`.

With a 5:1 ratio of Cl to compound, that is:
`0.01185 xx 5 = 0.0592` moles of `Cl`.