Question #8e917

1 Answer
Stefan V.
Jan 4, 2018

2 * 10^(23)

Explanation:

The trick here is to realize that the molar mass of oxygen gas tells you the mass of 6.022 * 10^(23) molecules of oxygen gas.

Since oxygen gas has a molar mass of about "32.0 g mol"^(-1), you can say that 6.022 * 10^(23) molecules of oxygen gas will have a mass of "32.0 g".

This is the case because 1 mole of oxygen gas must contain a number of molecules of oxygen gas equal to Avogadro's constant.

color(blue)(ul(color(black)("1 mole O"_2 = 6.022 * 10^(23)color(white)(.)"molecules O"_2)))

So if 1 mole of oxygen gas has a mass of "32.0 g", you can say that 6.022 * 10^(23) molecules of oxygen gas will have mass of "32.0 g".

This means that your sample contains

8 color(red)(cancel(color(black)("g"))) * (6.022 * 10^(23)color(white)(.)"molecules O"_2)/(32.0color(red)(cancel(color(black)("g")))) = color(darkgreen)(ul(color(black)(2 * 10^(23)color(white)(.)"molecules O"_2)))

The answer must be rounded to one significant figure, the number of sig figs you have for the mass of oxygen gas.

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