What is the dilution factor for a solution containing 100 g of NaCl made up to 500 mL with distilled water?

• A. 1:5 or 1/5
• B. 5
• C. 50 or 1/50
• D. 10

Answer: (A)

Dilution factor tells you how much the concentration drops when you dilute with solvent. Here, 100 g of NaCl ends up in a total volume of 500 mL, so the final concentration is 100 g / 500 mL = 0.2 g/mL. If that same 100 g were in 100 mL, the concentration would be 1.0 g/mL. The final concentration is one fifth of the stock concentration, so the dilution factor is 1/5 (often written as 1:5).