When considering concepts in chemistry like colligativeproperties, one might conjure up a mental picture of liquids bubbling insidebeakers in some lab. In reality,chemistry is involved in all functions of everyday life, even taking placewithin your own body. Envision kidneydialysis, a procedure prescribed by doctors when a person’s kidney’s fail. The kidneys, when operating normally, filterout toxins in the bloodstream like potassium and sodium and expel them as urine,and they regulate the body’s electrolyte levels. Kidney dialysis, more specificallyhemodialysis, artificially removes these toxins from the blood when the kidneysfail. Once a vein and artery have beenjoined together, blood is pumped out of the body, where it is externallyfiltered via a dialyzer, then it reenters the body, toxin-free.The dialyzer separates molecules based on size by passingthe blood and a liquid substance called dialyzer by each other through thedialysis membrane.
Necessary materialslike proteins and blood cells are too large to fit through the miniscule perforationsin the membrane, but products of waste that the kidneys can’t filter out passthrough the membrane into the dialysate. The cleaned blood is pumped back into the bloodstream, and the patientcan continue on their way. This mixtureof dialysate is discarded as waste, but something interesting has occurred withits colligative properties.Colligative properties refer to the qualities of solutionsthat fluctuate when the amount of solute particles is increased, no matter thesolute or solvent.
For example,dialysate is usually comprised of a mixture of distilled water, bicarbonate, andan acidified solution. When theparticles of waste from unfiltered blood enter the dialysate, it gains moresolute, and therefore more particles moving around in the solution. This change will cause the boiling point to raise,the freezing point to lower, and the vapor pressure to decrease.The vapor pressure (defined as “the pressure exerted by gasparticles as they exist in equilibrium with their condensed counterpart in aclosed system”) is physically affected by solute particles, especially if thesolute particles do not evaporate. Thenormal rate of evaporation, caused by innate kinetic energy of phase-changingmolecules, is decreased as solute particles occupy space that solvent particlesuse to break free of bonds. The boiling pointis made more extreme because of the vapor pressure; since the vapor pressure islowered, the boiling point will be made greater because it takes more energy toraise the vapor pressure to the atmospheric pressure. The freezing point is tampered with by thesolute particles, since as the solvent particles slow and bond due to the lowertemperatures, the solute particles interfere with the solidificationprocess.
Therefore, lower temperaturesoverall are needed to freeze the solution.Conversely, the blood that reenters the body exhibits theopposite colligative properties, since not much solvent has been lost, but theamount of solute particles in the organic blood solution has decreased. This means that the filtered blood has alower boiling point, a higher freezing point, and a higher vapor pressure. However, the patient is given more time andcomfort with their cleaned blood, and as long as they keep up with theirrequired dialysis schedule, they can continue to live a normal life.