text: Activity is used as an effective form of this quantity for non-ideal systems.
full_question: Activity is used as an effective form of this quantity for non-ideal systems. Peak size in HPLC is proportional to this value. The magnitude of properties dependent on this quantity is proportional to this quantity's product with the van't Hoff factor. This quantity is conventionally represented using square brackets. This non-partial pressure quantity is used along with the stoichiometric coefficient to define equilibrium constants. Colligative properties are dependent on this quantity, which can be found via a titration. For 10 points, name this quantity which can be measured in molarity which for a solution refers to how much solute is in some amount of solvent.
first_sentence: Activity is used as an effective form of this quantity for non-ideal systems.
raw_answer: concentration [prompt on molarity or molality]