How many moles are 1.20 x 1025 aloms of phosphorous?

can you show the work and explaining how you got the answer.

Feb 23, 2018

$19.969$ moles or $20.0$ moles using significant figures

Explanation:

A mole is a unit of measurement, but more specifically, it is an amount. Just like a dozen of a thing means 12 things, a mole measures the amount of something. The number of a certain thing in a mole is $6.022 \cdot {10}^{23}$; that number is called Avogadro's number. So a mole of potatoes is $6.022 \cdot {10}^{23}$ potatoes, or a mole of cars is $6.022 \cdot {10}^{23}$ cars.

This can be applied to chemistry to help convert between atoms to grams. The beauty of Avogadro's number is that $6.022 \cdot {10}^{23}$ molecules of a certain compound weighs its atomic mass in grams. For example, iron trichloride $F e C {l}_{3}$ has an atomic mass of 162.195. So a mole of $F e C {l}_{3}$ weighs 162.195 grams.

Now that the concept of moles is established, you know that a mole of anything has $6.022 \cdot {10}^{23}$ things in it. For phosphorous or any chemical compound, a mole contains $6.022 \cdot {10}^{23}$ molecules in it. So if you have $1.20 \cdot {10}^{25}$ (that's what I assume you meant) atoms of phosphorous, then just divide by Avogadro's number to find the number of moles.

(1.20* 10^25 ATOMS)/ (6.022*10^23 (ATOMS)/(MOL)

You would get $19.969$ moles. (Notice how when you simplify the units, you will end up with just moles which is the right unit.)