solute
Summary
A solute is the substance dissolved in a solvent to form a solution, and it is usually the component present in the smaller amount. Most testable: colligative properties depend on the number of dissolved solute particles, so a dissociating ionic solute has a larger effect than a molecular one at the same molarity.
Detail
Meaning: A solute is the substance dissolved in a solution, usually the component present in the smaller amount. The solvent is the larger component, such as water in an aqueous solution. Ionic solutes dissociate into ions, while molecular solutes such as glucose stay intact. Dissolving is favored when solute–solvent attractions compensate for the interactions that must be broken (like dissolves like).
Equation: M = nsolute / Vsolution, where M is molarity (mol/L; SI mol/m³), nsolute is the moles of solute (mol), and Vsolution is the volume of the whole solution (L; SI m³).
On the MCAT: Colligative properties (boiling point elevation, freezing point depression, vapor pressure lowering, osmotic pressure) depend on the number of dissolved solute particles, not on their identity. So 0.1 M CaCl₂ (about 3 particles per formula unit) has a larger effect than 0.1 M NaCl (about 2), which has a larger effect than 0.1 M glucose (1). Diluting adds solvent but leaves the moles of solute unchanged (M₁V₁ = M₂V₂).
Common confusion: Molarity divides by the volume of the whole solution, not the volume of solvent. Also, concentration of solute is not the same as concentration of particles: one mole of an ionic solute releases more than one mole of particles when it dissociates.
Sources
- Chemistry: The Central Science
- General Chemistry: Principles and Modern Applications
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.