Clear water can contain a complicated particle inventory — Physical Science: Chemistry

Dissolving a solute does not erase its mass or guarantee its formula remains an intact entity. Molecular solutes, hydrated ions and species that react with water require different models. A saturated solution with excess solid can keep exchanging material through equal dissolution and crystallization rates. Stirring can speed the approach without changing the fixed-condition equilibrium capacity.

Molarity uses liters of final solution; molality uses kilograms of solvent. A solution diluted without reaction or loss retains its solute amount while concentration falls. These definitions cannot be exchanged by relabeling a number. Use density and composition when a conversion between mass and volume conventions is needed.

Colligative approximations depend on effective dissolved-particle amount. One formula mole of an ideally dissociated salt can yield more than one mole of ions, but real association and nonideality alter effective behavior. Freezing shifts and osmotic pressure are phase/chemical-potential effects, not a claim that particles simply block water from freezing. Membrane selectivity and opposing pressure matter in an osmotic comparison.