If you have 7 molecules of #SO_2# gas in #2.617 * 10^5# molecules of air, what is the concentration of #SO_2# in ppm?
All you have to do here is use the definition of parts per million, or ppm.
You can use parts per million to express the concentration of a solution that contains very, very small amounts of solute. As its name suggests, this way of expressing concentration uses parts of solute per one million parts of solvent.
#color(blue)(|bar(ul(color(white)(a/a)"ppm" = "parts of solute"/"parts of solvent" xx 10^6color(white)(a/a)|)))#
In order to have a
Now, you can consider air to be your solution and sulfur dioxide,
This means that the concentration of sulfur dioxide in ppm will be
#"ppm SO"_2 = (7 color(red)(cancel(color(black)("molecules"))))/(2.617 * 10^5color(red)(cancel(color(black)("molecules")))) xx 10^6 = color(green)(|bar(ul(color(white)(a/a)"27 ppm"color(white)(a/a)|)))#
I'll leave the answer rounded to two sig figs.
So, this tells you that out of