Concentration
and
Dilution of Solutions
SOLUTION
“The Procedure”
We’ll make a Kool-Aid Solution!!!
Problem: How would you prepare 100 mL of a 2.5
g/L solution of Kool-aid?
#1. CALCULATE HOW MUCH SOLUTE YOU NEED
( Translation: How much SOLID Kool-aid is needed? )
Concentration = g of solute/L of solution
#2: Mass the amount of solute that YOU calculated
on a balance.
0.25 g of solute
#3: Take an appropriately sized volumetric flask. Fill
roughly half the volumetric flask with water.
(if you are making a 100 mL solution, the volumetric flask must be 100 mL)
#4. Using the weighing boat, carefully add the ___ g
of solute into volumetric flask.
#5. SWIRL the volumetric flask until all the solute
has properly dissolved.
#6. Add water until the calibration line. Make sure
the bottom of the meniscus is on the line!!!!
7. Cap and INVERT (carefully!) the volumetric
flask. (This is to make sure that the solution is
mixed).
In Class Example #1
How would you prepare 250 mL of a 5g/L NaCl
solution?
In Class Example #2
How would you prepare 250 mL of a 5%(m/v) NaCl
solution?
Arrange the following four solutions in
increasing concentration?
1) 2.5 g/L
2) 3.0 g/L
3) 1.3 g/L
4) 1.45 g/L
PROCEDURE ON HOW TO
DILUTE A SOLUTION
A dilution of a solution is a less-concentrated form of that solution.
We dilute a solution by adding more solvent.
How would you prepare 200 mL of a 1.0 g/L
solution of Kool-aid from the original 2.5 g/L
solution?
You MADE this solution!
Concentration: 2.5 g/L
You have 100 mL
You WANT this solution!
Concentration: 1.0 g/L
You WANT 200 mL
1.
Calculate how MUCH of your original solution is
required (the Vc!).
CcV
c
Vd
= Cd
Cc = Concentration of the CONCENTRATED solution
Vc = Volume of the CONCENTRATED solution
Cd = Concentration of the DILUTED solution
Vd = Volume of the DILUTED solution
Calculation
CcV
c
Vd
= Cd
(2.5 g/L)* Vc = 1.0 g/L * 200 mL
Vc = 1.0 g/L * 200 mL
(2.5 g/L)
Vc = 80 mL
3. Pour the 80 mL of concentrated
solution into the volumetric flask.
Vc = 80 mL
2. Take out 80 mL and put it in
the graduated cylinder
4, Add water until the 200 mL
mark.
200 mL
5. INVERT.
Serial Dilutions
If we wanted to make a 0.001g/mL solution of salt water
(or a 1:1000 solution) what would be an easy way to do so?
We could take 1g of salt, and add it to 1000mL (or 1L) of water
(1g/1000mL = 0.001g/mL)
What is one problem with this setup?
We now have 1 L of our solution! This is a lot – what if we only need 10mL?
Serial dilutions allow you to use small amounts of
various dilutions to reach the concentration you want.
Serial dilutions are usually made in increments of
10, 100 or 1000
Figure illustrating
serial dilutions
Using our formula CcVc=CdVd we can start by making 10mL of
a 1:10 dilution (can also be written as 0.1 or 10%):
C1 = 1 (full strength original)
V1 = this is what we are trying to find
C2 = 0.1 (10% or 1:10)
V2 = 10mL
Doing the math:
1V1 = 0.1 x 10
V1 = 1mL
So, to get 10mL of a 1:10 solution, we must add 1mL of our
stock solution to 9mL of water
Now that we have a 1:10 dilution, we can use it to make
10mL of a 1:100 dilution (0.01 or 1%)
C1 = 0.1
V1 = trying to find this
C2 = 0.01
V2 = 10mL
Doing the math:
0.1V1 = 0.01 x 10
V1 = 1mL
So, to get 10mL of a 1:100 dilution, we add 1mL of
our 1:10 dilution to 9mL of water
Now that we have a 1:100 dilution, we can use it to make 10mL
of a 1:1000 dilution (0.001 or 0.1%)
C1 = 0.01
V1 = trying to find this
C2 = 0.001
V2 = 10mL
Doing the math:
0.1V1 = 0.01 x 10
V1 = 1mL
So, we can add 1mL of our 1:100 dilution to 9mL of
water to get 10mL of a 1:1000 dilution!
PROBLEMS
1. How would you prepare 1L of saline(salt) solution with a
concentration of [10-1].
2. How would you prepare 1L of a [10-2] saline solution using your
[10-1] stock solution from question 1.
3. You have 10 mL of a [10-2] solution. How would you prepare a 10
mL [10-3] solution using the solution available to you in the lab?
4. You have 1000 mL of a [10-1] stock salt solution.
a. How would you make 35 mL of a [10-2] salt solution using your
stock solution? SHOW ALL YOUR WORK AND INDICATE A
PROCEDURE.
b. How would you make 50 mL of a [10-3] salt solution from part a?
SHOW ALL YOUR WORK AND INDICATE A PROCEDURE.