Preparing a solution and then diluting it?

Question

You have been asked to prepare 500.0 mL of a solution of calcium nitrate with a molarity of 5.6 M. Describe how it's made, showing all calculations and units. Then, you have been asked to dilute it to 2.0 M and a volume of 250.0 mL. What volume of the original solution must be diluted?

Answer 1

Ca(NO₃)₂ has a molar mass of 164.09 g.

 

 

Since we are preparing half a liter, we will use half of the moles required.

 

5.6 moles/2 = 2.8 moles

 

2.8 moles x (164.09 g/mole) = 459.44 g

 

So, a 500 mL of 5.6 M Ca(NO₃)₂ solution requires 459.44 grams.

 

 

 

To dilute the solution, use C₁V₁ = C₂V₂, which conserves then number of moles.

 

(5.6 M)V₁ = (2.0 M)(230 mL)

 

V₁ = 82.1 mL

 

Use 82.1 mL of 5.6 M solution and add enough water to get a final volume of 250 mL.