The formula for aluminum sulfate is #Al_2(SO_4)_3#. What is the molar mass of aluminum sulfate to the nearest gram?

1 Answer
Jun 12, 2017

Answer:

#"342 g mol"^(-1)#

Explanation:

The idea here is that the molar mass of aluminium sulfate, #"Al"_ 2("SO"_4)_color(blue)(3)#, will be equal to the sum of the molar masses of all the atoms that make up a mole of this compound.

As you can see, #1# mole of aluminium sulfate contains

  • two moles of aluminium, #2 xx "Al"#
  • three moles of sulfur, #color(blue)(3)xx "S"#
  • twelve moles of oxygen, #color(blue)(3) xx 4 xx "O"#

Now, grab a Periodic Table and look for the molar masses of aluminium, sulfur, and oxygen

  • #M_ ("M Al") = "26.981538 g mol"^(-1)#
  • #M_ ("M S") = "32.065 g mol"^(-1)#
  • #M_ ("M O") = "15.9994 g mol"^(-1)#

In order to find the molar mass of aluminium sulfate, you will need to do

#2 xx M_ ("M Al") + color(blue)(3) xx M_ ("M S") + 12 xx M_ ("M O")#

You will thus have

#2 xx "26.981538 g mol"^(-1) + color(blue)(3) xx "32.065 g mol"^(-1) + 12 xx "15.9994 g mol"^(-1)#

which will get you

#M_ ("M Al"_ 2("SO"_ 4)_ 3) = "342.150876 g mol"^(-1)#

Rounded to the nearest gram, the answer will be

#M_ ("M Al"_ 2("SO"_ 4)_ 3) = color(darkgreen)(ul(color(black)("342 g mol"^(-1))))#