If 200ml of a 4M solution of NaOH and 300ml of a 6M solution of NaOH are mixed what will the molarity of the resulting solution be?

1 Answer
May 16, 2018

The molarity of the #"NaOH"# mixture is #"5.2 M"# or #"5.2 mol/L"#.

Explanation:

#"molarity"=("mol solute")/("L of solution")#

To determine the molarity of the mixture of the two solutions, you need to convert the volume of each solution from mL to L. Then you need to determine the mol NaOH in each solution by multiplying the molarity of each solution by its volume in L.

Then you determine the total moles and total volume. Determine the molarity of the mixture by using the molarity formula, with the total moles and total volume.

#"4 M NaOH solution":#

#"molarity"="4 mol"/"L"#

#"volume"=200color(red)cancel(color(black)("mL"))xx(1"L")/(1000color(red)cancel(color(black)("mL")))="0.2 L"#

#"mole"_"NaOH"="molarity"xx"volume"="4 mol"/color(red)cancel(color(black)("L"))xx0.2color(red)cancel(color(black)("L"))="0.8 mol NaOH"#

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#"6 M NaOH solution":#

#"molarity"="6 mol"/"L"#

#"volume"=300color(red)cancel(color(black)("mL"))xx(1"L")/(1000color(red)cancel(color(black)("mL")))="0.3 L"#

#"mole"_"NaOH"="6 mol"/color(red)cancel(color(black)("L"))xx0.3color(red)cancel(color(black)("L"))="1.8 mol NaOH"#

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Molarity of the mixture of the two solutions

Add the moles of the two solutions.

#"Total moles"="0.8 mol NaOH + 1.8 mol NaOH"="2.6 mol NaOH"#

Add the volumes of the two solutions.

#"Total volume"="0.2 L + 0.3 L"="0.5 L"#

The molarity of the mixture is the total moles divided by the total volume.

#"M NaOH mixture"="2.6 mol"/"0.5 L"="5.2 mol/L"#