Dilution Worksheet
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1
2CHEMISTRY
DILUTION PRACTICE
Dilution: Definition and Calculations
Example #2
To dilute a solution means to add more
100.0 mL of 2.500 M KBr solution is on hand.
solvent without the addition of more solute. Of
You need 0.5500 M. What is the final volume of
course, the resulting solution is thoroughly
solution which results?
mixed so as to ensure that all parts of the
solution are identical.
Placing the proper values into the dilution
equation gives:
The fact that the solute amount stays constant
allows us to develop calculation techniques.
(2.500 mol/L) (100.0 mL) = (0.5500 mol/L) (x)
First, we write:
x = 454.5 mL
moles before dilution = moles after dilution
Sometimes the problem might ask how much
more water must be added. In this last case,
From the definition of molarity, we know that
the answer is 454.5 - 100.0 = 354.5 mL.
the moles of solute equals the molarity times
the volume.
Go ahead and answer the question, if your
teacher asks it, but it is bad technique in the
So we can substitute MV (molarity times
lab to just measure out the "proper" amount of
volume) into the above equation, like this:
water to add and then add it. The volumes are
not necessarily additive. The only volume of
M 1 V 1 = M 2 V 2
importance is the final solution's volume. You
add enough water to get to that volume without
caring how much the actual volume is.
The "sub one" refers to the situation before
dilution and the "sub two" refers to after
Practice Problems
dilution. We will call this the dilution equation.
1. A stock solution of 1.00 M NaCl is available.
This equation does not have an official name
How many milliliters are needed to make
like Boyle's Law, so
100.0 mL of 0.750 M
Example #1
53.4 mL of a 1.50 M solution of NaCl is on
hand, but you need some 0.800 M solution.
How many mL of 0.800 M can you make?
Using the dilution equation, we write:
2. What volume of 0.250 M KCl is needed to
make 100.0 mL of 0.100 M solution?
(1.50 mol/L) (53.4 mL) = (0.800 mol/L) (x)
Solving the equation gives an answer of 100.
mL.
Notice that the volumes need not be converted
to liters. Any old volume measurement is fine,
just so long as the same one is used on each
side.
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