# What is the mass, in grams, of a single iridium atom (#m_Ir = "192.22 u"#)?

##### 1 Answer

#### Answer:

#### Explanation:

The idea here is that you need to use the definition of the **unified atomic mass unit**, *in grams*.

The **unified atomic mass unit** is defined as

I will not go into the derivation here, but try to remember that the conversion factor that takes you from *unified atomic mass units* to *grams per mole* looks like this

#"1 u" = "1 g mol"^(-1)#

In your case, the mass of a single iridium atom is said to be equal to **molar mass** of iridium will be equal to

#192.22 color(red)(cancel(color(black)("u"))) * "1 g mol"^(-1)/(1color(red)(cancel(color(black)("u")))) = "192.22 g mol"^(-1)#

Finally, use **Avogadro's number** to help you convert between the mass of **one mole** of iridium atoms and the mass of a single iridium atom.

#"192.22 g"color(red)(cancel(color(black)("mol"^(-1)))) * overbrace((1color(red)(cancel(color(black)("mol"))))/(6.022 * 10^(23)"atoms"))^(color(brown)("Avogadro's number")) = color(green)(3.1920 * 10^(-22)"g")#

The answer is rounded to five **sig figs**.