M7Lesson #2Standard solutions
Lesson #1
Lesson #3

Topics
Calculating Concentrations
Molarity
Percent, ppm and ppb.
Dilution
Standard Solutions

Standard Aqueous Solutions

To create a standard aqueous solution of known concentration the following technique is typically used :

  1. The amount of solute needed and the volume of the solution are determined.
  2. Using volumetric flasks, add 1/2 of the volume of the solution .
  3. The solute is then measured out and added to this solution.
  4. The solute is then dissolved in the water and the remainder of the solution is added.
Example:

Describe how to create 600 ml of a 2.4 M solution of CaCl2 (aq) .

1. Determine the amount of solute.

Moles of CaCl2 (aq) = Concentration (M) * Volume (L) Moles of CaCl2 (aq) = 2.4 M * 0.600 L
Moles of CaCl2 (aq) = 1.44 moles
Mass of CaCl2 (aq) = moles * gram molecular wt.
Mass of CaCl2 (aq) = 1.44 moles * 110.95 g/mol
Mass of CaCl2 (aq) = 159.7 grams

2. Using a volumetric flash add 300 ml to the flask.
3. Mass out 159.7 grams of CaCl2 (s) and add to 300 ml.
4. Dissolve the CaCl2 (s) and add the remaining 300 ml.

 

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Serial Dilution

Serial dilution are solutions with concentrations that decrease by a set amount each time.

To create a serial dilution the total volume of solution must remains constant.

  1. Decide upon what will be the total volume of all of the solution samples in the dilution series
  2. Decide upon how many diluted solutions are needed and calculate the volumes of the original solutions needed to create the dilution.
  3. To create the first dilution , the calculated volume of the original solution is measured out and then more solvent is added to make the volume up to the desired total volume.
  4. To create the remaining dilution in the series , progressively smaller volumes of the original solution are used ( usually decreasing in standard intervals ) and made up to the desired total volume.
  5. To calculate the concentration of the dilution the dilution formula may be used.

Examples and Assignments

 

Example:

Create 4 serial dilution of a 8.0 M solution and calculate their concentrations.

1. Determine the total volume you wish to use:

Total volume = 100 ml

2. What is the # of dilution required :

# of dilution = 4

3. Decide upon the volumes of the original solutions , termed the stock solution that will be used to create the dilution . (decrease by 20 ml each time )

4. The following chart describes how to create the solutions.

#
Volume of Stock solution
Volume of Water
Total volume
1
80
20
100
2
60
40
100
3
40
60
100
4
20
80
100

5. Apply dilution formula to calculate concentrations

#
Concentration
Calculation
Dilution
Concentration
1
8.0 M * 80 ml/100 ml =
6.4 M
2
8.0 M * 60 ml/100 ml =
4.8 M
3
8.0 M * 40 ml/100 ml =
3.2 M
4
8.0 M * 20 ml/100 ml =
1.6 M
 
 

 

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Check your understanding

  1. Describe how to create 200 ml of a 5 % NaCl solution .
  2. Describe how to create 5 serial dilution of this salt solution.
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Assignment : Standard solutions and Serial dilution

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