01Definition
Dilution means lowering the concentration of a solution by adding solvent. The amount of solute stays the same, but it is spread through a larger total volume.
If you start with a concentrated stock solution and add water, buffer, or media, the final solution has a lower concentration. This is why dilution calculations are built around conservation of solute.
02Concentration Units
Molarity, written M, means moles of solute per litre of solution. Millimolar, micromolar, and nanomolar are smaller molarity units used for dilute solutions.
Mass concentration units such as mg/mL and µg/mL are common in biology and pharmacy. Percent and ppm are also concentration units, but converting them to molarity requires the molar mass of the solute.
- 1 M = 1000 mM
- 1 mM = 1000 µM
- 1 mg/mL = 1 g/L
- ppm in dilute water solutions is often treated as mg/L
03The Relationship
Dilution is inverse proportionality. If the final volume doubles while the amount of solute stays constant, the concentration halves.
That relationship is summarized by C1V1 = C2V2. The left side describes solute before dilution, and the right side describes the same solute after dilution.
04Real-World Examples
A student may dilute a 2.0 M NaCl stock to prepare 0.10 M NaCl for a practical. A microbiology lab may dilute a bacterial culture before plating colonies.
Other everyday examples include diluting bleach for cleaning, preparing saline, or making a working solution from a concentrated reagent bottle.
05Why Dilution Matters in a Lab
Most lab protocols depend on working concentrations. A reagent that is too concentrated can damage cells, change reaction rates, or invalidate calibration curves.
Good dilution technique also improves reproducibility. Recording stock concentration, final volume, pipette volumes, and units makes the calculation checkable later.
06Common Mistakes
The most common mistake is confusing final volume with solvent volume. If a calculation says V1 = 2 mL and V2 = 10 mL, you add 8 mL of solvent, not 10 mL.
Another frequent mistake is mixing units without converting them. C1 and C2 must be compatible, and V1 and V2 must be compatible before solving.
- Use total final volume for V2.
- Use stock volume for V1.
- Do not treat 1:10 as 1 part stock plus 10 parts solvent.
- Keep extra digits until the final answer.
07Frequently Asked Questions
Q1What does dilution mean in chemistry?
Dilution means reducing concentration by adding solvent. The solute amount stays constant, while the total volume increases.
Q2Does dilution change the number of moles?
No, not for an ordinary dilution. The number of moles of solute stays the same unless a reaction, loss, or transfer error occurs.
Q3What happens to concentration when volume increases?
Concentration decreases in direct proportion to the volume increase. Doubling the volume halves the concentration.
Q4What is the formula for dilution?
The standard dilution formula is C1V1 = C2V2. It follows from n = CV, where n is the amount of solute.
Q5Is a 1:10 dilution ten times weaker?
Yes. A 1:10 dilution has one tenth of the original concentration, assuming the ratio means one part stock in ten parts total.
Q6Can dilution be used for cells?
Yes. Cell suspensions are often diluted using the same logic, with concentration expressed as cells per mL.
Q7Why is final volume important?
Final volume is the total volume after stock and solvent are combined. It is not the same as the amount of solvent added.
Q8Can dilution calculations have uncertainty?
Yes. Pipette tolerance, stock concentration uncertainty, and final volume readings all contribute uncertainty to the prepared concentration.
Ready to calculate?
Use the free dilution calculator to solve C1V1 = C2V2, dilution factors, and serial dilution tables.
Open the Dilution Calculator →