Question #a0144

1 Answer
Sep 22, 2015

#3.0 * 10^(24)"atoms"#


To find the number of atoms of copper you have in 320 g of copper, you first need to find out how many moles of copper you have.

Once you get the number of moles you have in 320 g of copper, you can use its molar mass to find the number of atoms.

An element's molar mass simply tells you what the mass of one mole of that element is.

In copper's case, its molar mass is equal to #"63.546 g/mol"#. This means that every mole of copper has a mass of #"63.546 g"#.

The number of moles of copper you have is

#320color(red)(cancel(color(black)("g"))) * "1 mole Cu"/(63.546color(red)(cancel(color(black)("g")))) = "5.036 moles Cu"#

Now, use the fact that one mole of any element contains exactly #6.022 * 10^(23)# atoms of that element - this is known as Avogadro's number.

In your case, 5.036 moles would contain

#5.036color(red)(cancel(color(black)("moles Cu"))) * (6.022 * 10^(23)"atoms of Cu")/(1color(red)(cancel(color(black)("mole Cu")))) = color(green)(3.0 * 10^(24)"atoms of Cu")#

The answer is rounded to two sig figs.