Dilution calculation example: How do you prepare 100 ml of 0.40 M MgSO₄ from a stock solution of 2.0 M MgSO₄?

There are two solutions involved in this problem. Notice that you are given two concentrations, but only one volume.

• Solution #1 is the one for which you have only concentration - the solution that is already sitting on the shelf.
   
• Solution #2 is the one for which you have both concentration and volume - the solution that you are going to prepare.

At least until you are comfortable with this type of problem, it may be helpful to write out what numbers go with what letters in the equation before beginning.

M₁ = 2.0 M MgSO₄       V₁ = unknown

M₂ = 0.40 M MgSO₄       V₂ = 100 ml

To solve the problem, do the following:

• Write the equation: M₁ V₁ = M₂ V₂
   
• Manipulate the equation: V₁ = M₂ V₂ / M₁
   
• Put numbers into the equation: V₁ = (0.40M) (100 ml) / 2.0 M
   
• Do the calculation: V₁ = 20 ml
   
• Describe preparing the solution as follows: Add 80 ml of distilled water to 20 ml of the 0.40 M MgSO₄ solution.

Combined Molarity and Dilution Calculations

Molarity Calculation Assignment #2

 
Computer Lab