Materials Included In Kit

Additional Materials Required

Safety Precautions

Exercise caution when working with scissors as they are sharp. Always cut away from yourself and others. Please follow all classroom safety guidelines.

Sample Data

Dilution of concentrated acetic acid, CH₃CO₂H, 17.4 M

All dilutions are calculated using the following equation: M₁V₁ = M₂V₂

To make 1.0 liter of 6 M acetic acid

M₁ = 17.4 Molar
V₁ = unknown
M₂ = 6.0 Molar
V₂ = 1.0 Liter

To make 1.0 liter of 3.0 M acetic acid

M₁ = 17.4 Molar
V₁ = unknown
M₂ = 3.0 Molar
V₂ = 1.0 Liter

 

To make 1.0 liter of 1.0 M acetic acid

M₁ = 17.4 Molar
V₁ = unknown
M₂ = 1 Molar
V₂ = 1.0 Liter

To make 1.0 liter of 0.50 M acetic acid

M₁ = 17.4 Molar
V₁ = unknown
M₂ = 0.50 Molar
V₂ = 1.0 Liter

To make 1.0 liter of 0.01 M acetic acid

M₁ = 17.4 Molar
V₁ = unknown
M₂ = 0.10 Molar
V₂ = 1.0 Liter

Introduction

Solutions are an important part of chemistry. Sometimes space and storage requirements do not permit having every concentration of each solution. Learn how to dilute acid and base solutions to obtain the desired concentration.

Concepts

• Concentration
• Dilution equation
• Molarity

Background

The amount of solute that is dissolved in a given quantity of solvent is called the concentration of the solution. A dilute solution contains only a small amount of solute in a given amount of solution, while more concentrated solutions contain larger amounts of solute in a given amount of solution. Molarity is most commonly used to describe the concentration of a solution. The molarity, M, of a solution is defined as the number of moles of solute in one liter of solution (Equation 1).

Experiments often require a solution that is more dilute than what is on hand in the stockroom. In this case, a more concentrated stock solution must be diluted to obtain the desired concentration. To carry out a dilution, the following equation is used. In this equation, Molarity _{concentrated soln}, is the concentration of the stock solution, volume_{concentrated soln} is the volume of the stock solution required to prepare the dilute solution, Molarity_{dilute soln} is the concentration of the desired dilute solution, and volume_{dilute soln} is the volume of the dilute solution needed. The dilution equation is commonly written as Equation 3. The subscripts 1 and 2 refer to the concentrated and the dilute solutions, respectively. For example, assume that a 0.80 M sodium chloride solution is in the stockroom, but for another experiment, 100 mL of a 0.20 M sodium chloride solution is needed. In performing a dilution calculation, M₁, M₂ and V₂ are generally known and Equation 3 is rearranged to solve for the unknown V₁. Substituting the known values for this example into Equation 4 allows us to solve for the volume of the stock solution required to prepare the dilute solution. Thus, diluting 25 mL of 0.80 M sodium chloride to a final volume of 100 mL will result in a 0.20 M solution. Proper analytical technique for preparing the diluted solution requires that the initial and final volumes (V₁ and V₂) must be accurately measured using a graduated cylinder or, preferably, a pipet and a volumetric flask.

Materials

Safety Precautions

Exercise caution when working with scissors. Always cut away from yourself and others. Please follow all classroom safety guidelines.

Procedure

1. Concentrated acetic acid, CH₃CO₂H, also known as glacial acetic acid, is 17.4 M. Using Equation 4 from the Background section, determine the volume of concentrated acetic acid required to make 1.0 L of 6.0 M acetic acid solution.
2. Using a black pen, copy this volume into the box located in the upper right corner (containing the asterisk) of the Dilutions Calculator Insert (see Figure 1).
   {12387_Procedure_Figure_1_Dilution calculator insert}
3. Calculate the volume of concentrated acetic acid needed to make 1.0 L of 3.0 M acetic acid.
4. Using a black pen, copy this volume in the box to the left of the 6.0 M concentration.
5. Calculate the volume of 17.4 M acetic acid necessary to make 1.0 L of each of the following dilutions—1.0 M, 0.50 M and 0.10 M.
6. Write these values in the corresponding boxes in the first row on the Dilutions Calculator Insert in the order shown. Color in each box with a colored pencil according to the following scheme. Color in all the boxes on the insert by the column. All the boxes in the far left column should be purple, all the boxes in the second column should be blue, and so on.
   {12387_Procedure_Figure_2}
7. Concentrated or reagent acids and bases are defined as those that contain the maximum amount of dissolved acid or base in water at room temperature. These reagents are the most common stock solutions used to prepare dilute acids and bases for use in the lab. Repeat steps 1–6 to calculate the volume required of each concentrated acid or base reagent to make 1.0 L of all of the following dilutions—6 M, 3 M, 1 M, 0.5 M and 0.1 M. The molarity of each concentrated acid or base is shown after the formula.

   Hydrochloric acid, HCl, 12.1 M
   Nitric acid, HNO₃, 15.8 M
   Phosphoric acid, H₃PO₄, 14.8 M
   Sulfuric acid, H₂SO₄, 18 M
   Ammonium hydroxide, NH₄OH, 14.8 M

8. Write the answers in the corresponding boxes on the Dilutions Calculator Insert according to the order noted. Hydrochloric acid in row 2, nitric acid in row 3 and so on.
9. Using scissors, carefully cut out the squares and side-tab on the Dilution Calculator envelope. Note: Always cut away from yourself and others.
10. Fold the envelope in half and place the Dilution Calculator Insert into the envelope.
11. Tape the envelope closed on the bottom.