how do i work this problem

Question

A

toy

top

has

a

mass

of

32.0

g Cu

.

How

many

atoms Cu

are

in

this

spinning

top,

given

that

the

average

atomic

mass

of

copper

is

63.55

g/mol Cu

?

Answer 1

It's a dimensional analysis problem. You multiply or divide quantities to convert your units for the amount of Cu from grams to moles to number of atoms.

Notice how in each step the original unit, in the numerator of the first term and in the denominator of the second, cancels.

32 g × 1mol/(63.55 g) = (32/63.55) mol

This step uses the atomic mass of Cu to convert g to mol

(32/63.55) mol × 6.022 × 10²³ atoms/mol = (32/63.55)(6.022 × 10²³) atoms

This step uses Avagadro's number (6.022 × 10²³) to convert mol to atoms

So there are 3.03 × 10²³ atoms of Cu in the spinning top.