Molality

Molality, denoted m, is defined as the number of moles of solute dissolved per kilogram of solvent (not per kilogram or litre of the whole solution): $\text{Molality } (m) = \dfrac{\text{no. of moles of solute}}{\text{mass of solvent in kg}}$. Because molality is built entirely from masses — the moles of solute and the mass of solvent — and mass, unlike volume, does not change with temperature, molality itself does not change with temperature, which makes it a more robust concentration unit than molarity for work where the temperature is not tightly controlled. In the laboratory, a solution of some desired, lower concentration is very often prepared by diluting a solution of known, higher concentration with more solvent; that starting, more concentrated solution is called a stoc …