Diluting Solutions

Chemicals are shipped around the world is their most concentrated forms(solids, concentrated acids, etc)


For example.You have a 5.0 mg/L phosphate standard that exceeds the upper test limit for the low-range phosphate analytical procedure. For it to be considered adequate for a QA/QC known-concentration sample you’ll need to dilute it to a 0.2 mg/L concentration. Can you easily and accurately make this dilution?

Or your 6 N sodium hydroxide solution is too strong to properly adjust the pH of BOD samples. Instead, a 1 N solution would give greater control. How much of the 6 N solution would you need to dilute to get a 1 N solution?

There are also many other instances in a wastewater laboratory where the dilution of an acid, a base, or a laboratory standard is required so that when the resulting solution is used in an analytical procedure, it will help you attain the most accurate result.

The formula for diluting these types of solutions is simple:

(volumeA)(concentrationA) = (volumeB)(concentrationB)

Here are two examples using this formula:

#1) You want to make 250 mL of a 0.20 mg/L phosphate solution from a stock solution of 5.0 mg/L. How much of the 5.0 mg/L phosphate stock solution will you need to dilute to 250 mL so that the resulting concentration is 0.20 mg/L phosphate?

Put the information into the formula: (250 mL)(0.20 mg/L) = (X mL needed)(5.0 mg/L)
Then solve for X: (X mL needed) = (250 mL)(0.20 mg/L)/(5.0 mg/L) = 10 mL

Take 10 mL of the 5.0 mg/L phosphate solution and dilute it to 250 mL with distilled water (10 mL of solution with 240 mL water). The resulting solution will be 250 mL with a concentration of 0.20 mg/L phosphate.