Question #bc514

1 Answer
Jun 2, 2016

Here's what I got.


The idea here is that you need to use a conversion factor that can take you from number of molecules to moles.

This conversion factor is called Avogadro's number and it's actually the definition of a mole.

In simple terms, a mole is just a very, very large collections of atoms or molecules, depending on what substance you're dealing with.

In order to have one mole of a substance, you need to have a fixed number of atoms of that substance. More specifically, you need to have

#color(blue)(|bar(ul(color(white)(a/a)"1 mole" = 6.022 * 10^(23)"atoms"color(white)(a/a)|))) -># Avogadro's number

Now, sodium, #"Na"#, does not exist as molecules, so the question should actually sound like this

How many moles are in * #1 xx 10^(24)# atoms of sodium?*

So, you know that a mole is defined as a collection of #6.022 * 10^(23)# atoms, which means that this many atoms will be equivalent to

#1 * 10^(24)color(red)(cancel(color(black)("atoms Na"))) * overbrace("1 mole Na"/(6.022 * 10^(23)color(red)(cancel(color(black)("atoms Na")))))^(color(blue)("Avogadro's number")) = "1.66 moles Na"#

You need to round this off to one sig fig, the number of sig figs you have for the number of atoms of sodium

#"no. of moles" = color(green)(|bar(ul(color(white)(a/a)color(black)("2 moles Na")color(white)(a/a)|)))#