Colligative properties and osmotic pressure

Chemical Potential The chemical potential of a substance i is the partial molar derivative of the free energy G, the enthalpy H, the Helmholtz energy A, or the internal energy U of substance i: Matter flows spontaneously from a region of high chemical potential to a region of low chemical potential just like electric current flows from a region of high electric potential to a region of low electric potential and mass flows from a position of high gravitational potential to a position of low gravitational potential. The chemical potential can therefore be used to determine whether or not a system is in equilibrium. When the system is in equilibrium, the chemical potential of each substance will be the same in all the phases appearing in the system.

Colligative properties and osmotic pressure

Colligative Properties Photo by: Fedor Kondratenko Colligative properties are those properties of solutions that depend on the number of dissolved particles in solution, but not on the identities of the solutes. For Colligative properties and osmotic pressure, the freezing point of salt water is lower than that of pure water, due to the presence of the salt dissolved in the water.

To a good approximation, it does not matter whether the salt dissolved in water is sodium chloride or potassium nitrate; if the molar amounts of solute are the same and the number of ions are the same, the freezing points will be the same.

For example, AlCl 3 and K 3 PO 4 would exhibit essentially the same colligative properties, since each compound dissolves to produce four ions per formula unit. The four commonly studied colligative properties are freezing point depression, boiling point elevation, vapor pressure lowering, and osmotic pressure.

Since these properties yield information on the number of solute particles in solution, one can use them to obtain the molecular weight of the solute.

Freezing Point Depression The presence of a solute lowers the freezing point of a solution relative to that of the pure solvent. If one uses sucrose table sugar instead of sodium chloride, 10 grams 0. The reason that the salt solution has a lower freezing point than the sugar solution is that there are more particles in 10 grams 0.

Physical properties of liquids

Since sucrose, C 12 H 22 O 11 has a molecular weight of In addition, each sodium chloride unit comes apart into two ions a sodium cation and a chloride anion when The freezing point depression of a solution containing a dissolved substance, such as salt dissolved in water, is a colligative property.

Sucrose is a nonelectrolyte, which means that the solution contains whole C 12 H 22 O 11 molecules. In predicting the expected freezing point of a solution, one must consider not only the number of formula units present, but also the number of ions that result from each formula unit, in the case of ionic compounds.

This formula is approximate, but it works well for low solute concentrations. Because the presence of a solute lowers the freezing point, many communities put salt on their roads after a snowfall, to keep the melted snow from refreezing.

Also, the antifreeze used in automobile heating and cooling systems is a solution of water and ethylene glycol or propylene glycol ; this solution has a lower freezing point than either pure water or pure ethylene glycol.

Boiling Point Elevation The boiling point of a solution is higher than that of the pure solvent. Accordingly, the use of a solution, rather than a pure liquid, in antifreeze serves to keep the mixture from boiling in a hot automobile engine.

As with freezing point depression, the effect depends on the number of solute particles present in a given amount of solvent, but not the identity of those particles. If 10 grams 0. As with the freezing point depression formula, this one is most accurate at low solute concentrations. Vapor Pressure Lowering The vapor pressure of a liquid is the equilibrium pressure of gas molecules from that liquid i.

A glass of water placed in an open room will evaporate completely and thus never reach equilibrium ; however, if a cover is placed on the glass, the space above the liquid will eventually contain a constant amount of water vapor.

Colligative properties and osmotic pressure

How much water vapor is present depends on the temperature, but not on the amount of liquid that is present at equilibrium provided some liquid is present at equilibrium.

At room temperature, the vapor pressure of pure water is about 20 Torr, which is about one-fortieth of the total atmospheric pressure on a "normal" day at sea level. If, instead of pure water, an aqueous solution is placed in the glass, the equilibrium pressure will be lower than it would be for pure water.

Raoult's law states that the vapor pressure of the solvent over the solution is proportional to the fraction of solvent molecules in the solution; that is, if twothirds of the molecules are solvent molecules, the vapor pressure due to the solvent is approximately two-thirds of what it would be for pure solvent at that temperature.

If the solute has a vapor pressure of its own, then the total vapor pressure over the solution would be: One consequence of this lowering in vapor pressure may be observed in a spilled can of soda. As the water evaporates, the soda becomes more sugar and less water, until the vapor pressure of the water is so low that it barely evaporates.

As a result, the spilled soda remains sticky for a long time. Contrast this behavior with that of a water spill.

Osmotic Pressure Osmosis is the process whereby a solvent passes through a semipermeable membrane from one solution to another or from a pure solvent into a solution.

A semipermeable membrane is a barrier through which some substances may pass e. Important examples of semipermeable membranes are the cell walls in cells of living things plants and animals.AIIMS Entrance Exam Syllabus. Get the updated AIIMS Entrance Exam Syllabus from this page.

All India Institute of Medical Sciences MBBS Entrance Exam Syllabus based on Physics, Chemistry, and Biology concepts. Reverse osmosis is a separation process that uses pressure to force a solvent through a semi-permeable membrane that retains the solute on one side and allows the pure solvent to pass to the other side, forcing it from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.

Colligative properties and osmotic pressure

What Is Osmotic Pressure? Osmosis is the movement of water from an area of low concentration of solute to an area of higher concentration of solute. A solute is atoms, ions, or molecules dissolved.

Liquid: Liquid, in physics, one of the three principal states of matter, intermediate between gas and crystalline solid. The most obvious physical properties of a liquid are its retention of volume and its conformation to the shape of its container. Learn more about the properties and behavior of .

Colligative Properties.

ChemCollective: Properties of Solutions

Molecular Science Modules; Osmotic pressure Molecular Science Module. When a balloon is filled to near bursting with SF6 is left in air, it will often burst after a period of time. What Is Osmotic Pressure? Osmosis is the movement of water from an area of low concentration of solute to an area of higher concentration of solute.

A solute is atoms, ions, or molecules dissolved.

Colligative properties of solutions