# Calculate the mass of 3.920 × 10 to the power of 25 atoms of phosphorus?

##### 2 Answers

#### Explanation:

You can use dimensional analysis to convert units easily for this problem.

Start with your

You also need to use the molar mass of Phosphorus, which is

You can set it up like this:

You can go ahead and cancel out units that appear on both the top and the bottom of the fraction:

You can see that the unit will be grams, which makes sense as the question asks for mass.

You can multiply across to make your expression look like this:

Simplify the top row to get this:

And finally, divide to get:

#### Explanation:

#"1 mol of atoms = 6.022 × 10"^23\ "atoms"#

Number of moles of phosphorus atoms given is

#3.920 × 10^25 cancel"atoms" × "1 mol"/(6.022 × 10^23\ cancel"atoms") = "65.09 mol"#

Molar mass of phosphorus is

Then, mass of phosphorus in given sample

#65.09 cancel"mol" × 30.97 "g"/cancel"mol" ≈ "2016 g"#