Meaning and mechanism
Molar concentration c is the amount of solute, in moles, per 1 L of solution. If the solute mass is known, divide it by molar mass to find the amount n in moles.
Adding only water without reaction or loss leaves the amount of solute unchanged while increasing solution volume. The same solute distributed through a larger volume has a lower concentration.
Relationships and conditions
c=n/V, so if n is conserved during dilution, c₁V₁=c₂V₂. Diluting 100 mL of a 1 mol/L solution to a final volume of 500 mL gives 0.2 mol/L.
If some solution is discarded or reaction, evaporation, or precipitation occurs, check again whether conservation of the solute amount in moles applies. The sum of different solution volumes is not always exactly the final volume.
What to observe in the simulation
If you only add water, the moles of solute are conserved and the concentration is inversely proportional to the final solution volume. g/L is mass concentration, mol/L is molar concentration.
A hypothetical solute with a molar mass of 100 g/mol. It is assumed that the entire amount is dissolved, there is no loss, and there is no reaction, and saturation is not addressed. The input volume is the final solution volume, not the solvent volume. Volume non-additivity is not calculated. g/L is not a mass percentage.
Key relationships and symbols
n = m/M · c = n/V · c₁V₁ = c₂V₂
| Symbol | Meaning | Unit |
|---|---|---|
| c | Molar concentration | mol/L |
| n | Amount of solute | mol |
| V | Final solution volume | L |
Worked example
What is preserved when diluted by adding only water?
If there is no solute loss or reaction, n is the same. Since c₁V₁ = c₂V₂, 0.5 × 0.100 / 0.500 = 0.1 mol/L.
Common misconceptions
- Adding 500 mL of water is different from making the final solution volume up to 500 mL.