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Phase diagram for an aqueous solution of a nonelectrolyte

The colligative effects on vapor pressure, boiling point, and freezing point described in the previous section are conveniently summarized by comparing the phase diagrams for a pure liquid and a solution derived from that liquid. Phase diagrams for water and an aqueous solution are shown in [link] .

This phase diagram indicates the pressure in atmospheres of water and a solution at various temperatures. The graph shows the freezing point of water and the freezing point of the solution, with the difference between these two values identified as delta T subscript f. The graph shows the boiling point of water and the boiling point of the solution, with the difference between these two values identified as delta T subscript b. Similarly, the difference in the pressure of water and the solution at the boiling point of water is shown and identified as delta P. This difference in pressure is labeled vapor pressure lowering. The lower level of the vapor pressure curve for the solution as opposed to that of pure water shows vapor pressure lowering in the solution. Background colors on the diagram indicate the presence of water and the solution in the solid state to the left, liquid state in the central upper region, and gas to the right.
These phase diagrams show water (solid curves) and an aqueous solution of nonelectrolyte (dashed curves).

The liquid-vapor curve for the solution is located beneath the corresponding curve for the solvent, depicting the vapor pressure lowering , Δ P , that results from the dissolution of nonvolatile solute. Consequently, at any given pressure, the solution’s boiling point is observed at a higher temperature than that for the pure solvent, reflecting the boiling point elevation, Δ T b , associated with the presence of nonvolatile solute. The solid-liquid curve for the solution is displaced left of that for the pure solvent, representing the freezing point depression, Δ T b , that accompanies solution formation. Finally, notice that the solid-gas curves for the solvent and its solution are identical. This is the case for many solutions comprising liquid solvents and nonvolatile solutes. Just as for vaporization, when a solution of this sort is frozen, it is actually just the solvent molecules that undergo the liquid-to-solid transition, forming pure solid solvent that excludes solute species. The solid and gaseous phases, therefore, are composed solvent only, and so transitions between these phases are not subject to colligative effects.

Osmosis and osmotic pressure of solutions

A number of natural and synthetic materials exhibit selective permeation , meaning that only molecules or ions of a certain size, shape, polarity, charge, and so forth, are capable of passing through (permeating) the material. Biological cell membranes provide elegant examples of selective permeation in nature, while dialysis tubing used to remove metabolic wastes from blood is a more simplistic technological example. Regardless of how they may be fabricated, these materials are generally referred to as semipermeable membranes .

Consider the apparatus illustrated in [link] , in which samples of pure solvent and a solution are separated by a membrane that only solvent molecules may permeate. Solvent molecules will diffuse across the membrane in both directions. Since the concentration of solvent is greater in the pure solvent than the solution, these molecules will diffuse from the solvent side of the membrane to the solution side at a faster rate than they will in the reverse direction. The result is a net transfer of solvent molecules from the pure solvent to the solution. Diffusion-driven transfer of solvent molecules through a semipermeable membrane is a process known as osmosis    .

The figure shows two U shaped tubes with a semi permeable membrane placed at the base of the U. In figure a, pure solvent is present and indicated by small yellow spheres to the left of the membrane. To the right, a solution exists with larger blue spheres intermingled with some small yellow spheres. At the membrane, arrows pointing from three small yellow spheres on both sides of the membrane cross over the membrane. An arrow drawn from one of the large blue spheres does not cross the membrane, but rather is reflected back from the surface of the membrane. The levels of liquid in both sides of the U shaped tube are equal. In figure b, arrows again point from small yellow spheres across the semipermeable membrane from both sides. This diagram shows the level of liquid in the left, pure solvent, side to be significantly lower than the liquid level on the right. Dashed lines are drawn from these two liquid levels into the middle of the U-shaped tube and between them is the term osmotic pressure.
Osmosis results in the transfer of solvent molecules from a sample of low (or zero) solute concentration to a sample of higher solute concentration.

When osmosis is carried out in an apparatus like that shown in [link] , the volume of the solution increases as it becomes diluted by accumulation of solvent. This causes the level of the solution to rise, increasing its hydrostatic pressure (due to the weight of the column of solution in the tube) and resulting in a faster transfer of solvent molecules back to the pure solvent side. When the pressure reaches a value that yields a reverse solvent transfer rate equal to the osmosis rate, bulk transfer of solvent ceases. This pressure is called the osmotic pressure ( Π )    of the solution. The osmotic pressure of a dilute solution is related to its solute molarity, M , and absolute temperature, T , according to the equation

Questions & Answers

what's an hydroxyl group?
VICTORY Reply
A hydroxy or hydroxyl group is the entity with the formula OH. It contains oxygen bonded to hydrogen. In organic chemistry, alcohols and carboxylic acids contain hydroxy groups. The anion [OH⁻], called hydroxide, consists of a hydroxyl group. 
okwara
what are the steps to follow when writing the condensed formula of elements
Jessicafaith Reply
What is organic chemistry
John Reply
what's organic chemistry?
Mr Reply
why do electrons have no mass
Skynetic Reply
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Samuel
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Oliver
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Eyong
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Lagazani
please what is maa
Lagazani
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divine
Because it's mass it very very small compare with mass of atom
Yasmeen
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lola
consider the rxn of butadiene .Butadiene is prepared by the gas phase catalytic dehydrogenation of 1-butene , at 900K and 1 bar. c4H8 (g)_ C4H6 (g) + H2 (g) (a) In order to suppress side reactions , the butane is diluted with steam before it passes into the reactor.Estimate the conversion
Rodrick
Estimate the conversion of 1-butene for a feed consisting of 10 moles of steam per mole of 1-butene. (b) find the conversion if the inerts were absent and side reactions are ignored .
Rodrick
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Rodrick
wat is the difference between electrochemical chemical corrosion
Uzor
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Lagazani
what is the definition of chemistry
Sophia Reply
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Eyong
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Eyong
for now chemistry is the study of matter and it properties, why and how element combined to form other substances
Eyong
Chemistry is a group that identifies properties of matter and many more
Alona
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Eyong
chemistry is the study of the structure, properties of matter and the effect of addition or removal of heat from substances.
Bra
calculate the relative molecular Mass of the following 1 ZnCl2 2 NaNo3 3 HNO3 4 CaO
Reuben Reply
2) 23+14+(16×3)= 3)1+14+(16×3)= 4) 40+16= 1) Zn+71= that's how they do it but for Zn I don't know its mass number
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Christian
What is radioactivity
Aaron Reply
radioactivity is the spontaneous disintegration of the nucleus of an atom of an element to emmit radiation
Vivian
When dividing a certain and uncertain number, you still use sig figs? Ex: 12.86g divided by 12 M&Ms
Kristen Reply
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Christian
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Alanna
organic chemistry as a whole
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Judith
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Judith
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ueah
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Judith answer
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Abraham
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Christian
wat is periodicity of element
Abraham
Abraham periodicity is the trend of variation in the property of element in the periodic table with increased in atomic number but is mostly on physical properties
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Justice
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Eyong
what is an atom
Lawal Reply
An atom is the smallest part of matter that cannot break down further by chemical means
Alanna
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Eyong
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Christian
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Christian
an atom is the smallest indivisible particle of an element.
Vivian
atom can be broken down into smaller particle which are the proton electron and neutron
Vivian
what is chemistry
Moses Reply
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Vivian
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Christian
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Vivian
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Justice
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Eyong
How can I get to understand better and faster?
Sunday Reply
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omachonu
When water is added to NaOH, the solution becomes hot in the initial stage. Why?
jeffreto
why so you say the the zero after a decimal point is a significant number.... whiles it does not change the value of the numbers involved
Esther Reply
atom is electrically neutral because...
Vivian Reply
why will someone ask a question and answer it by him or her self
Vivian
Because number of positive proton equal number of negative electron
Yasmeen

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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