Which expression is correct for a dilution factor of 10 when a 1 mL sample is added to 9 mL diluent?

• A. Sample volume divided by final volume.
• B. Final volume minus sample volume.
• C. Final volume / sample volume.
• D. Final volume multiplied by sample volume.

Answer: (C)

Dilution factor tells you how many times the sample has been spread into the final mixture, and it is the ratio of the final total volume to the volume of sample you started with. Here, you add 1 mL of sample and bring the total volume to 10 mL (1 mL sample + 9 mL diluent). So the dilution factor is 10 mL divided by 1 mL, which equals 10. That’s why the expression final volume divided by sample volume is the correct way to represent the dilution factor.

If you instead used sample volume divided by final volume, you’d get 0.1, which is the reciprocal and represents the fraction of the final solution that came from the original sample, not the dilution factor. Subtracting the volumes gives the diluent amount (9 mL), and multiplying the volumes has no meaningful interpretation for dilution.