Dilutions

What is a Dilution?

Dilution is the process of decreasing the concentration of a solution by adding a solvent. The total number of solutes in the solution remains the same after dilution, but the volume of the solution becomes greater, resulting in a lower molarity, ppm, mg/L, or % concentration.  

In the picture above,  the solute is shown as yellow dots and the solvent as solid blue.  The 1 L beaker on the left shows the initial concentration, which represents 13 dots/L.  The beaker on the right is the result of dilution of the left beaker.  After adding more solvent so that the solution's total volume becomes 3 L, the concentration of the diluted beaker is (13 dots)/(3 L), or 4.3 dots/L.

As mentioned, there are two components to any solution and these are:

• Solvent: Does the dissolving (In most cases the solvent is water)
• Solute: Is dissolved  

*An easy way to remember how to distinguish the two and what they do, note that the longer word, SOLVENT takes over the shorter word SOLUTE*  

How Do We Calculate Dilutions:

Recall that concentration (M) is also written as mol/L. From this we can write C=n/V and n=CV. Dilution calculations are simplified by using the following equation:

C₁V₁ = C₂V₂ 

Where: 

• C₁ = concentration of the first solution
• V₁ = volume of the first solution
• C₂ = concentration of the second solution
• V₂ = volume of the second solution

Example One: 

Determine the concentration when 200 mL of 0.60 M HCl is diluted to a final volume of 300 mL:

• C₁ = 0.6 M
• V₁ = 200 mL
• C₂ = ?
• V₂ = 300 mL 

C₁V₁ = C₂V₂  

(C₁V₁) / V₂ = C₂  

((0.60)(200)) / 300 = C₂ 

_{0.4 M = C2}   

Example Two: 

How much water must be added to 5.0mL of 40.0M Na2SO4 to a solution with a concentration of 0.50M?

• C₁ = 40.0 M
• V₁ = 5.0 mL
• C₂ = 0.50 M
• V₂ = ? 

C₁V₁ = C₂V₂  

(C₁V₁) / C₂ = V₂  

((40.0)(5.0)) / 0.5 = V₂ 

_{400 mL = V2}    


Attached is a video with more information on dilutions:

-Simon Sierra