| 
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Dilution, Equation 5.3
Parts of this equation/concept include:
molality = moles of solute/kilograms of solvent
initial volume initial
concentration = final volumefinal
concentration
MiVi = MfVf
| A. Determining Concentration
if a Solution Is Diluted |
>> Example 1
What is the molarity of a solution made by diluting 5.00 mL of
1.8 M H2SO4 to a volume of 250.0 mL?
Solution:
Note that you start and end with the same type of solution, which
makes it different from the previous problem. The key word diluting
also tells you that you want the following equation:
MV = MV
The only other trick to solving this is to make sure that units
match on each side of the equals sign (but you can use whatever
volume units you like) and that you keep the concentrated (low
volume, high molarity) numbers together and the diluted numbers
together.
(1.8 M)(5.00 mL) = (x M)(250.0 mL)
| (1.8 M)(5.00 mL) |
|
| 250.0 mL |
|
= |
x |
0.036 M = x
Don't forget significant figures.
>> Example 2
What is the concentration when 10.00 mL of 1.36 M NaCl
is diluted to make 1.00 L of solution?
Solution:
The units on volume are not the same. You must either convert
milliliters to liters or liters to milliliters. It doesn't matter
which.
| 1.00 L |
|
|
= |
1000 mL |
(1.36 M)(10.00 mL) = (x M)(1000 mL)
0.0136 M = x
or
| 10.00 mL |
|
|
= |
0.01000 L |
(1.36 M)(0.01000 L) = (x M)(1.00 L)
0.0136 M = x
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| B. Determining How to
Dilute a Solution to a Specific Concentration |
>> Example 3
How would you make 500.0 mL of a 0.10 M HNO3
solution from 16 M HNO3?
Solution:
This is still a dilution problem. The concentration is changing
but not the identity of the solution. Solve for what you don't
know, making sure to keep units the same and volumes and concentrations
together as before.
MV = MV
(0.10 M)(500.0 mL) = (16 M)(V)
3.1 mL = V
Notice that this does not really answer the question. The question
asks for directions. In this example the directions should go
something like this: “Add 3.1 mL of the 16 M acid
to a 500.0-mL volumetric flask that already contains some water.
Mix carefully. Slowly, with mixing, add solvent (water) until
the level of liquid reaches the mark on the volumetric flask.”
>> Example 4
What volume of 0.10 M KI(aq) is required to make
100.0 mL of 0.01 M KI(aq)?
Solution:
This is also a dilution problem.
MV = MV
(0.1 M)V = (0.01 M)(100.0 mL)
V = 10 mL
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