How many molecules of nitrogen monoxide are in a 22.5 gram sample?
Your strategy here will be to use the molar mass of nitric oxide,
Once you know that, you can use Avogadro's number as a conversion factor to help you determine how many molecules would be present in that many moles.
So, nitric oxide has a molar mass of
Since your sample is about
More precisely, you will have
#22.5 color(red)(cancel(color(black)("g"))) * " 1 mole NO"/(30.01 color(red)(cancel(color(black)("g")))) = "0.7498 moles NO"#
Now, according to Avogadro's number, one mole of any substance contains
#0.7498 color(red)(cancel(color(black)("moles NO"))) * overbrace((6.022 * 10^(23)"molec. NO")/(1color(red)(cancel(color(black)("mole NO")))))^(color(purple)("Avogadro's number")) = "4.5153 molec. NO"#
Rounded to three sig figs, the number of sig figs you have for the mass of nitric oxide, the answer will be
#"no. of molecules" = color(green)(|bar(ul(color(white)(a/a)4.52 * 10^(23)color(white)(a/a)|)))#