Cryoscopy: Definition, History, Materials Needed, Procedure, Observations and Calculations

It is the process used to determine the reduced freezing points produced in the liquid by dissolved substances to determine the molecular weights of the solutes.

It is defined as the difference in the freezing points of the pure solvent and the solution.

Cryoscopy is considered one of the modern solution theory and physical chemistry foundations.

The study focuses on identifying the steps that helped, first qualitatively and then quantitatively, to fit the other possible solutions, including those that formed hydrates, to a fundamental formulation that the French scientist François-Marie Raoult would later generalize in the law that bears his name.

Cryoscopy is the most widely used method in biological research to determine molecular concentration.

The cryoscopy method is also of considerable use in forensic medicine.

The most promising methods devised are cryoscopy, the methylene blue test, and the phloridzin test.


Since 1888, when Beckmann devised the first relatively sensitive apparatus for determining the freezing point of a solution, the medical use of this instrument, the cryoscope or osmometer, has been primarily limited to physiological and clinical research to measure total solute concentration. And osmotic pressure.

However, freezing point determination of biological fluids also has standard clinical value in evaluating specific urinary, electrolyte, and fluid abnormalities.

Like the other colligative properties, it allows the determination of the molecular weight of an unknown or unidentified substance based on the principle that the solution’s freezing point compared to that of the respective solvent varies according to the quantity and nature of the solute dissolved in it.


The excessively straightforward style used by most textbooks to present the historical events associated with the emergence, development, and discussion of laws, theories, and hypotheses related to scientific concepts tends to create in the reader a distorted or incomplete version of the facts. Real.

The history of the birth of cryoscopy as a scientific discipline is an excellent example of this situation.

The origins of cryoscopy (from the Greek roots, κρυοσ ice, and σκοπεω that I examine) have generally been associated, almost exclusively, with the name of the French chemistry professor François-Marie Raoult (1830-1901).

Through exact and systematic experimental work on this topic, he formulated a freezing point law that applies to water and other solvents, including solutes of organic and inorganic nature.

The very little information cited in physical chemistry textbooks on the different colligative properties shows that Raoult received the relevant information.

Accordingly, it would not be possible to know that the subsequent evolution of the subject was the result of many trials, successes, failures, approximations, and errors.

While it is true that he was not only responsible for the quantitative generalization of the connection between the decrease in the freezing point of a solution and its corresponding concentration, but also the proposed name for this branch of chemistry.

The first observations on this topic date back more than a century before Raoult’s investigations.

The specific terminology used by each of the scientists involved has been preserved as far as possible to support the presentation of extracts from the original papers, despite some confusion that it might cause.

Necessary materials

  • Water bath.
  • Test tube.
  • Thermometer.
  • Agitator.
  • Reagents


  • Water.
  • Benzene.
  • Carbon disulfide.
  • Carbon tetrachloride.
  • Chloroform.

Dissolute substance

  • Sodium chloride.
  • Calcium chloride.
  • Aluminum chloride.
  • Urea.
  • Glucose.


  1. Take the test tube from the water bath.
  2. Select a solvent component from the list.
  3. Choose a known amount of solvent.
  4. Place the thermometer in the test tube.
  5. Place the test tube in the water bath.
  6. Click on the power button.
  7. Record the temperature of the solvent.
  8. Click the shutdown button.
  9. Take the test tube from the water bath.
  10. Choose the solute from the list.
  11. Choose your weight.
  12. Place the test tube in the water bath.
  13. Click on the power button.
  14. Record the temperature of the solution.
  15. Use the freezing point of pure solvents to determine the freezing point depression.

Observations and calculations

  • The solvent used = …………………….
  • Mass of solvent = …………… g
  • The freezing point of pure solvent = ……………. oC
  • Solute used = …………………………..
  • Masa of the solute = ……………… g
  • Solution freezing point = …………………… oC
  • Therefore, depression at the freezing point of the solution = ………………… .. oC
  • The van ‘t Hoff factor of the solute = …………………….
  • The molar mass of the solute = …………………………

Points to remember while experimenting in a natural laboratory

  • Always wear gloves and a lab coat when in the lab.
  • When entering the lab, turn on the extraction fan and make sure all chemicals and reagents required for the run are available; if not available, prepare the reagents using the components.
  • Correctly set the Bunsen burner flame: the proper pet is a small blue cone; It is not a large feather, nor is it orange.
  • Make sure to clean your entire working apparatus with chromic acid and distilled water – make sure that all devices are free of water droplets while experimenting.
  • Be sure to calibrate the electronic weight balance before taking measurements.
  • Clean all glass containers with soap and distilled water: recap the reagent bottles once the experiment is complete.
  • Turn off the light, the extraction fan, and the gas cylinder before leaving the laboratory.
  • Dispose of used gloves in a garbage can.