Question #55cb4

1 Answer
Stefan V.
May 6, 2017

The answer is (a) 3.0 * 10^(19)

Explanation:

The first thing you need to do here is to convert the mass of ethanol to moles by using the compound's molar mass

2.3 * 10^(-3) color(red)(cancel(color(black)("g"))) * "1 mole ethanol"/(46.07color(red)(cancel(color(black)("g")))) = 4.992 * 10^(-5) "moles ethanol"

Now, you should know that a mole of a molecular compound contains 6.022 * 10^(23) molecules of said compound. This implies that 1 mole of ethanol will contain

color(blue)(ul(color(black)("1 mole ethanol" = 6.022 * 10^(23)color(white)(.)"molecules C"_2"H"_5"OH")))

You can thus say that your sample of ethanol will contain

4.992 * 10^(-5) color(red)(cancel(color(black)("moles C"_2"H"_5"OH"))) * (6.022 * 10^(23)color(white)(.)"molecules C"_2"H"_5"OH")/(1color(red)(cancel(color(black)("mole C"_2"H"_5"OH"))))

= color(darkgreen)(ul(color(black)(3.0 * 10^(19)color(white)(.)"molecules C"_2"H"_5"OH")))

The answer is rounded to two sig figs.

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