How many molecules are in 35.5 g of "Cl"_2Cl2 ?

1 Answer
Stefan V.
Jul 30, 2016

3.02 * 10^(23)3.02⋅1023

Explanation:

Your strategy here will be to

  • use the molar mass of chlorine gas, "Cl"_2Cl2, to calculate how many moles you have in that sample
  • use Avogadro's number to convert the number of moles to number of molecules

![http://www.elementlearning.com/blog.php

Chlorine gas has a molar mass of "70.906 g mol"^(-1)70.906 g mol−1, which tells you that one mole of chlorine gas has a mass of "70.906 g"70.906 g. Use the molar mass as a conversion factor to help you go from grams of chlorine gas to moles

35.5 color(red)(cancel(color(black)("g"))) * "1 mole Cl"_2/(70.906color(red)(cancel(color(black)("g")))) = "0.5007 moles Cl"_235.5g⋅1 mole Cl270.906g=0.5007 moles Cl2

Now, a mole of a molecular compound is defined as 6.022 * 10^(23)6.022⋅1023 molecules of said compound ->→ this is known as Avogadro's number.

In your case, the sample of chlorine gas will contain

0.5007 color(red)(cancel(color(black)("moles Cl"_2))) * (6.022 * 10^(23)"molec. Cl"_2)/(1color(red)(cancel(color(black)("mole Cl"_2)))) = color(green)(|bar(ul(color(white)(a/a)color(black)(3.02 * 10^(23)"molec Cl"_2)color(white)(a/a)|)))

The answer is rounded to three sig figs.

Related questions
See all questions in The Mole
Impact of this question
63567 views around the world
You can reuse this answer
Creative Commons License