Chemistry · Solution · Solubility / Principles and Exploration
Concentration and dilution — principles and investigation
When you only add water to a solution, the solute remains the same, but the amount of solute in the same volume decreases. Compare mass concentration and molar concentration by varying the solute mass and the final solution volume before and after dilution. It is important not to confuse the volume of water added with the total volume of the solution after dilution.
How does it work?
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.
n = m/M · c = n/V · c₁V₁ = c₂V₂
Try this investigation
- Determine the solute mass and solution volume before and after dilution. The water addition button increases the final solution volume by 100 mL.
- Maintain 5 g and run and record 100 mL and 500 mL conditions, respectively. The molar mass of the hypothetical solute is 100 g/mol.
- Compare the results of diluting to 1000 mL with the same solute and the results of diluting to 500 mL with only 10 g of solute.
Interpreting your results
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.
Assumptions and limitations
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.