Question #9be80

1 Answer
Sep 14, 2015

You have #"31.3 g"# of potassium in that much potassium sulfate.


The idea here is that you need to use the number of moles of potassium that you get per mole of potassium sulfate, #"K"_2"SO"_4#.

If you look at the formula unit of potassium sulfate, you'll notice that it contains

  • two potassium atoms #-># you get that from the #2# subscript;
  • one sulfur atom
  • four oxygen atoms #-># you get that from the #4# subscript.

This means that 1 mole of potassium sulfate will contain 2 moles of potassium, 1 mole of sulfur, and 4 moles of oxygen.

In your case, you have 0.400 moles of ptoassium sulfate, which means that you have

#0.400color(red)(cancel(color(black)("moles K"_2"SO"_4))) * "2 moles K"/(1color(red)(cancel(color(black)("moles K"_2"SO"_4)))) = "0.800 moles K"#

Now just use potassium molar mass to get the number of grams that would contain this many moles

#0.800color(red)(cancel(color(black)("moles K"))) * "39.0983 g K"/(1color(red)(cancel(color(black)("mole K")))) = color(green)("31.3 g K")#

Here's a list of videos on percent composition, check them out!