How many moles of #HNO_3# are needed to prepare 5.0 liters of a 2.0 M solution of #HNO_3#?

1 Answer
May 22, 2017

Answer:

#"10. moles"#

Explanation:

All you have to do here is to use the molarity of the solution as a conversion factor to determine the number of moles of solute that must be dissolved in #"5.0 L"# of solution in order to have a concentration of #"2.0 M"#.

As you know, molarity tells you the number of moles of solute present in #"1 L"# of solution. In your case, a #"2.0 M"# solution will contain #2.0# moles of solute for every #"1 L"# of solution.

Now, because solutions are homogeneous mixtures, i.e. they have the same composition throughout, you can use the molarity of the solution as a conversion factor to get the moles of solute needed for your solution

#5.0 color(red)(cancel(color(black)("L solution"))) * overbrace("2.0 moles HNO"_3/(1color(red)(cancel(color(black)("L solution")))))^(color(blue)("= 2.0 M")) = color(darkgreen)(ul(color(black)("10. moles HNO"_3)))#

The answer is rounded to two sig figs.

This tells you that dissolving #10.# moles of nitric acid in enough water to get the total volume of the solution to #"5.0 L"# will give you the same molarity as dissolving #2.0# moles of nitric acid in enough water to get the total volume of the solution to #"1.0 L"#.