# The atomic weight of aluminum is 26.982 u, how many aluminum atoms are there in a 4.55g sample of aluminum?

##### 1 Answer

#### Explanation:

The key to this problem is the correct interpretation of what *atomic weight* means.

Notice that aluminium is said to have an atomic mass of *unified atomic mass unit*,

The unified atomic mass unit is defined as **one nucleon**, as in the mass of one proton or one neutron. Also, you should know that you have

#"1 u" color(white)(x) = color(white)(x)"1 g/mol"#

This means that the mass of **one mole** of aluminium atoms will be

As you know, *one mole* of any element contains exactly

This means that if you know how many moles of aluminium you have in

#4.55 color(red)(cancel(color(black)("g"))) * "1 mole Al"/(26.982color(red)(cancel(color(black)("g")))) = "0.168631 moles Al"#

Therefore, you will have

#0.168631color(red)(cancel(color(black)("moles of Al"))) * (6.022 * 10^(23)"atoms of Al")/(1color(red)(cancel(color(black)("mole Al")))) = color(green)(1.02 * 10^(23)"atoms of Al")#

The answer is rounded to three sig figs, the number of isg figs you gave for the mass of the sample.