Question #dd197

1 Answer
Mar 18, 2016

Here's what I got.


The idea here is that you need to take the molar mass of each individual atom that makes up your compound and figure out the molar mass of the compound itself.

As you know, the molar mass of a substance tells you the mass of one mole of that substance. This means that you can convert from moles to grams, or vice versa, by using molar mass.

In your case, 1, 1-dichloroethane, #"CH"_3"CHCl"_2#, is made up of

  • two atoms of carbon, #2 xx "C"#
  • three atoms of hydrogen, #4 xx "H"#
  • two atoms of chlorine, #2 xx "Cl"#

Pull up a periodic table and look at the molar masses of carbon, hydrogen, and chlorine

#"For C: " M_M = "12.011 g mol"^(-1)#

#"For H: " M_M = "1.00794 g mol"^(-1)#

#"For Cl: " M_M = "35.4527 g mol"^(-1)#

This means that the molar mass of 1, 1 - dichloroethane will be

#overbrace(2 xx "12.011 g mol"^(-1))^(color(blue)("two atoms of C")) + overbrace(4 xx "1.00784 g mol"^(-1))^(color(purple)("four atoms of H")) + overbrace(2 xx "35.3527 g mol"^(-1))^(color(red)("two atoms of Cl"))#

#M_M = "98.76 g mol"^(-1)#

This tells you that one mole of 1, 1 - dichloroethane will have a mass of #"98.76 g"#.

For example, if you have a sample of #"125 g"# of this compound, you can use its molar mass, i.e. the mass of one mole, to calculate how many moles you get in the sample

#125 color(red)(cancel(color(black)("g"))) * overbrace(("1 mole CH"_3"CHCl"_2)/(98.76color(red)(cancel(color(black)("g")))))^(color(brown)("molar mass")) = "1.27 moles CH"_3"CHCl"_2"#