In this Demonstration, a trayed absorption column is used to remove an impurity solute (chloroform) from a gas feed by absorbing the impurity in a liquid solvent. The number of trays/stages needed to obtain a desired outlet solute mole ratio in the gas stream is calculated. A stage is a plate that contacts the liquid solvent and the gas to promote mass transfer. The slope of the pink operating line, L/V, is shown on the column on the right. The equilibrium line is orange.