Question #10db8

1 Answer
Jun 20, 2017

Answer:

#2.8 * 10^8# #"g"#

Explanation:

The thing to remember about the density of a substance is that it represents the mass of exactly one unit of volume of said substance.

#"density" = "mass of substance"/"1 unit of volume"#

In your case, the density of helium at STP is equal to #"0.1875 g L"^(-1)#, which means that under STP conditions, every #"1 L"# of helium has a mass #"0.1875 g"#.

#"0.1875 g L"^(-1) = "0.1875 g"/"1 L"#

Now, you know that the volume of the balloon is equal to #1.5 * 10^9# #"L"# under STP conditions.

Since you already know that you get #"0.1875 g"# of helium per #"1 L"#, use the density of the helium at STP as a conversion factor to find the mass present in your balloon

#1.5 * 10^9 color(red)(cancel(color(black)("L"))) * overbrace("0.1875 g"/(1color(red)(cancel(color(black)("L")))))^(color(blue)("the density of helium at STP")) =color(darkgreen)(ul(color(black)(2.8 * 10^8color(white)(.)"g")))#

The answer is rounded to two sig figs, the number of sig figs you have for the volume of the balloon.