solution
ColLigative properties of biological liquids.
Solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.
The physical properties of compounds such as melting point and boiling point change when other compounds are added. Together they are called colligative properties. There are several ways to quantify the amount of one compound dissolved in the other compounds collectively called concentration. Examples include molarity, mole fraction, and parts per million (PPM).
The properties of ideal solutions can be calculated by the linear combination of the properties of its components. If both solute and solvent exist in equal quantities (such as in a 50% ethanol, 50% water solution), the concepts of “solute” and “solvent” become less relevant, but the substance that is more often used as a solvent is normally designated as the solvent (in this example, water).
There are four quantities that describe concentration:
Homogenous means that the components and properties of the mixture are uniform throughout its entire volume. Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids, or solids. One or more components present in the solution other than the solvent are called solutes. The solution has the same physical state as the solvent.
If the solvent is a gas, only gases are dissolved under any given set of conditions. An example of a gaseous solution is air (oxygen and other gases dissolved iitrogen). Since interactions between molecules play almost no role, dilute gases form rather trivial solutions. In part of the literature, they are not even classified as solutions, but addressed as mixtures.
If the solvent is a liquid, then gases, liquids, and solids can be dissolved. Examples are:
* Gas in liquid:
Oxygen in water.
Carbon dioxide in water is a less simple example, because the solution is accompanied by a chemical reaction (formation of ions). Note also that the visible bubbles in carbonated water are not the dissolved gas, but only an effervescence of carbon dioxide that has come out of solution; the dissolved gas itself is not visible since it is dissolved on a molecular level.
* Liquid in liquid:
The mixing of two or more substances of the same chemistry but different concentrations to form a constant.(Homogenization of solutions)
Alcoholic beverages are basically solutions of ethanol in water.
* Solid in liquid:
Sucrose (table sugar) in water
Sodium chloride or any other salt in water forms an electrolyte: When dissolving, salt dissociates into ions.
Counterexamples are provided by liquid mixtures that are not homogeneous: colloids, suspensions, emulsions are not considered solutions.
Body fluids are examples for complex liquid solutions, containing many different solutes. They are electrolytes since they contain solute ions (e.g. potassium and sodium). Furthermore, they contain solute molecules like sugar and urea. Oxygen and carbon dioxide are also essential components of blood chemistry, where significant changes in their concentrations can be a sign of illness or injury.
If the solvent is a solid, then gases, liquids, and solids can be dissolved.
* Gas in solid:
Hydrogen dissolves rather well in metals, especially in palladium; this is studied as a means of hydrogen storage.
* Liquid in solid:
mercury in gold, forming an amalgam
Hexane in paraffin wax
* Solid in solid:
Steel, basically a solution of carbon atoms in a crystalline matrix of iron atoms.
Alloys like bronze and many others.
Polymers containing plasticizers.
Solubility
The ability of one compound to dissolve in another compound is called solubility. When a liquid is able to completely dissolve in another liquid the two liquids are miscible. Two substances that caever mix to form a solution are called immiscible.
All solutions have a positive entropy of mixing. The interactions between different molecules or ions may be energetically favored or not. If interactions are unfavorable, then the free energy decreases with increasing solute concentration. At some point the energy loss outweighs the entropy gain, and no more solute particles can be dissolved; the solution is said to be saturated. However, the point at which a solution can become saturated can change significantly with different environmental factors, such as temperature, pressure, and contamination. For some solute-solvent combinations a supersaturated solution can be prepared by raising the solubility (for example by increasing the temperature) to dissolve more solute, and then lowering it.
Colligative properties are properties of solutions that depend on the number of molecules in a given volume of solvent and not on the properties/identity of the molecules. Colligative properties include: relative lowering of vapor pressure; elevation of boiling point; depression of freezing point and osmotic pressure. Measurements of these properties for a dilute aqueous solution of a non-ionized solute such as urea or glucose can lead to accurate determinations of relative molecular masses. Alternatively, measurements for ionized solutes can lead to an estimation of the percentage of ionization taking place.
1. Vapour pressure
1. Mass concentration
The mass concentration ρi is defined as the mass of a constituent mi divided by the volume of the mixture V:
The SI-unit is kg/m3.
2. Molar concentration
The molar concentration ci is defined as the amount of a constituent ni divided by the volume of the mixture V:
The SI-unit is mol/m3. However, more commonly the unit mol/L is used.
3. Number concentration
The number concentration Ci is defined as the number of entities of a constituent Ni in a mixture divided by the volume of the mixture V:
The SI-unit is 1/m3.
4. Volume concentration
The volume concentration φi (also called volume fraction) is defined as the volume of a constituent Vi divided by the volume of all consituents of the mixture V prior to mixing:
The SI-unit is m3/m3.
5. Normality
Normality is defined as the molar concentration ci divided by an equivalence factor feq. Since the definition of the equivalence factor may not be unequivocal, IUPAC and NIST discourage the use of normality.
6. Molality
The molality of a solution mi is defined as the amount of a constituent ni divided by the mass of the solvent m solvent (not the mass of the solution):
The SI-unit for molality is mol/kg.
7. Mole fraction
The mole fraction xi is defined as the amount of a constituent ni divided by the total amount of all constituents in a mixture ntot:
The SI-unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole fractions.
8. Mole ratio
The mole ratio ri is defined as the amount of a constituent ni divided by the total amount of all other constituents in a mixture:
If ni is much smaller thatot, the mole ratio is almost identical to the mole fraction.
The SI-unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole ratios.
9. Mass fraction
The mass fraction wi is the fraction of one substance with mass mi to the mass of the total mixture mtot, defined as:
The SI-unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass fractions.
10. Mass ratio
The mass ratio ζi is defined as the mass of a constituent mi divided by the total mass of all other constituents in a mixture:
If mi is much smaller than mtot, the mass ratio is almost identical to the mass fraction.
The SI-unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass ratios.
Hypertonic Solution
A Hypertonic solution contain a high concentration of solute in relation to the solution within the cell (e.g. the cell’s cytoplasm).
When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel up.
Hypotonic Solution
A hypotonic solution contain A solution with a lower salt concentration than iormal cells
When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.
Isotonic Solution
A solution that has the same salt concentration as the normal cells of the body and the blood.
When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.
The water – main component of human organisms and also is part of medium, in which lives the people. The main water property is solved a lot of matters with formatted solutions.
The water in organisms of the person, animal, plant is by its constituent (in a yumrn’s organism about 70 -80 % of water), solvent, and also participates in exchange reactions of matters (hydrolysis, hydration, swelling (turgescence), digestion). It executes a role of a transport system in processes of a feeding, carry of enzymes, products of a metabolism, gases, antibodies. The water is supported a condition to a homeostasis in an organism of the person (acid – alkaline, osmotic, hemodinamicil, thermal equilibrium). The water is indispensable for secrets iones, maintenance of a turgor of cages.
SOLYTIONS. TYPES OF SOLYTIONS.
The solution is homogeneous thermodynamic nonperishable systems, which consist with two or stable more components.
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. The solvent does the dissolving. The solution more or less takes on the characteristics of the solvent including its phase, and the solvent is commonly the major fraction of the mixture. The concentration of a solute in a solution is a measure of how much of that solute is dissolved in the solvent.
MODERN THEORY ABOUT THE NATURE OF SOLUTIONS
The medical men are especially interested for liquors. The biological liquids (blood, the lymph, urine), wich is by complex mixtures of proteins, lipids, carbohydrates, salts. Physic-chemical regularity of interplay these miscellaneous behind properties and sizes of fragments both between itself, and with water moleculas ambient them, is extremely relevant for habitability of an organism.
During development of the doctrine about solutions two theories are designed: chemical and physical.
According to the physical theory (S. Arrenyus, V. Osvald, Ye. Vant-Hoff), the process of dissolution is esteemed as an even distribution particles of solvend in all volume of solution. The solvent is by inert medium, the moleculas of solvend and solvent do not interact between themselves.
The chemical theory (D. I. Mendelaev, I.A. Kablucov, M. S. Kurnacov) regarded solution as systems, which one were derivated from parts of solvend, solvent and non-persistent chemical combinations, which one will be derivated in solution with the help of hydrogen bindings, or electrostatic attractive forces at interplay particles of a solvent and solvend.
The modern theory of solutions integrates the physical and chemical theories regarded process formation of solutions as interplay between particles of different polarity.
An unsaturated solution is one in which the concentration of solute is less than its concentration in a saturated solution. (Additional solute can be dissolved in an unsaturated solution, until the solution becomes saturated.)
A supersaturated solution is one in which the concentration of solute is greater than its concentration in a saturated solution. A supersaturated solution is unstable and its solute tends eventually to crystallize out of solution, much as a supercooled liquid tends eventually to crystallize. Solubility equilibrium is not possible in a supersaturated solution. If more solute is added, crystallization occurs, usually rapidly, as solute leaves the solution to crystallize on the surfaces of the crystals of added solute. (The situation is very much like the rapid freezing of a supercooled liquid brought about by adding a seed crystal.)
The solubility of a solute in a given solvent is defined as the concentration of the saturated solution. At
SOLUTIONS OF GASES IN LIQUIDS
Henry’s Law: The solubility of a gas dissolved in a liquid is proportional to the partial pressure of the gas above the liquid.
This is a statement of Henry’s law, which can be written
X = KP
where X is the equilibrium mole fraction of the gas in solution (its solubility), P is its partial pressure in the gas phase, and K is a constant of proportionality, usually called the Henry’s-law constant.
The partial pressure is a part of common pressure, which one is a share of each gas in gas mixture.
Henry’s law applies only when the concentration of the solute and its partial pressure above the solution are both low, that is, when the gas and its solution are both essentially ideal, and when the solute does not interact
Oo-bottoms, where the external pressure increases, the dissolubility of gases in a blood is augmented. At fast ascent from depth the dissolubility sharply decreases, they are excreted by the way is bubble and seal vessels – aeroembolism.
Properties of a solution which depend only on the concentration of the solute and not upon its identity are known as colligative properties. These include vapor-pressure lowering, boiling-point elevation, freezing-point depression, and osmotic pressure. Each of these properties is a consequence of a decrease in the escaping tendency of solvent molecules brought about by the presence of solute particles. Escaping tendency is the tendency shown by molecules to escape from the phase in which they exist.
Osmosis.
Suppose а concentrated solution of copper sulphate (deep blue in colour) is placed in а beaker and water (or а dilute solution of copper sulphate) is added slowly along the walls of the beaker without much disturbing the concentrated copper sulphate solution. The two layers are more or less well defined. Now if the beaker is allowed to stand, it is observed that after а few days, the solution in the beaker becomes uniformly blue throughout. This must be obviously due to the fact that the particles of the solute (Cu+2 and SO4-2 ions) move slowly into the solvent and the molecules of the solvent (water) move into the copper sulphate solution. In other words, the particles of the solute and solvent mix spontaneously into each other.
Now suppose the experiment is performed in а slightly different manner. Suppose the beaker is divided into two compartments, by а semi-permeable membrane i.е. а membrane which allows the solvent molecules to pass through but not the solute particles. Suppose again that copper sulphate solution is placed in one compartment and water in the other. It is observed that the level on the solution side begins to rise. This must be obviously due to the fact that greater number of solvent (water) molecules from the solvent side pass into the solution side through the semi-permeable membrane than the number of solvent molecules going into the solvent from the solution through the semi-permeable membrane. Similarly, if а concentrated solution is separated from а dilute solution by а semi-permeable membrane, there is а net flow of solvent from the dilute solution to the concentrated solution through the semi-permeable membrane.
The spontaneous mixing of the particles of the solute (present in the solution) and the solvent (present above the solution) to form а homogeneous mixture is called diffusion, just as the term is used for the spontaneous mixing of gases to form homogeneous mixtures.
Difference between Diffusion and Osmosis. The main points of difference between diffusion and osmosis may be summed up as given below:
Osmosis:
1. In osmosis, а semi-permeable membrane is used.
2. In this process, there is only flow of solvent molecules and that too through the semi-permeable membrane.
3. It takes place from lower concentration to higher concentration.
4. It applies to solutions only.
5. It can be stopped or reversed by applying pressure on the solution with higher concentration.
Semi-permeable membranes. The semi-permeable membranes (as defined above) are of two types:
1) Natural semi-permeable membranes е.g vegetable membranes and animal membranes which are found just under the outer skin of the animals and plants. The pig’ s bladder is the most common animal membrane used.
2) Artificial semi-permeable membranes. The well known examples of the artificial semi-permeable membranes are parchment paper, cellophane and certain freshly precipitated inorganic substances е.у. copper ferrocyanide, silicates, of iron, cobalt, nickel etc. The precipitated substances have to be supported on some material and this is achieved by preparing the precipitate in the walls of а porous pot.
Osmotic Pressure – The upward movement of water taking place can be prevented if we apply mechanical force on top of the solution in the jar. The pressure just sufficient to stop osmotic pressure exerted by the solution in the jar will be the osmotic pressure exerted by the solution present in the jar. The osmotic pressure of а solution may thus be defined as the equivalent of excess pressure which must be applied, to the solution in order to prevent the passage of the solvent into it through а semi-permeable membrane separating the two, i.e. the solution and the pure solvent. Osmotic pressure may be defined as the equilibrium hydrostatic pressure of the column set up as а result of osmosis.
Expression for the osmotic pressure. Osmotic pressure (Р) of а solution is found to be directly proportional to the concentration (С) of the solution and its temperature (Т).
Р = CRT;
posmotic = Cosmotic RT;
Since molarity equals the number of moles of solute (n2) per liter of solution. V, that is. Since: C = n2/V;
PV= nRT – van’t Hoff equation for dilute solutions.
Measurement of osmotic pressure
The osmotic pressure of а solution can be measured by many methods, but only two methods will be described.
1. Pfeffer’s method – А very simple apparatus was used by Pfeffer for this purpose. А battery pot with а semipermeable membrane deposited in its wall is cemented to а wide glass tube which ends in а thin tube at the top and carries а manometer in the side. The manometer is closed at its upper end and is filled with Hg and N2. The solution under investigation is introduced into the pot through this tube, The apparatus is then made airtight by sealing off the tube at the top. А portion of the pot is immersed in distilled water kept at. а constant temperature. In the course of а few days, the manometer registers the maximum pressure, which is the osmotic pressure of the solution.
2. Freezing point determination method – It ha been found that there is а decrease of 1.8б0С in the freezing point of а solution when its osmotic pressure is0equal to one osmole. This method is much more rapid and accurate than Pfeffer’s method. A special apparatus is used to determine the freezing point о f the solution under investigation which is then compared with freezing point of the pure. solvent.
The decrease in the freezing point of the solution is one of the colligative properties of colloidal solutions. The other colligative properties e.g. elevation of boiling point and depression of the vapor density can also be used in the determination of the osmotic pressure of а solution.
Laws of osmotic pressure – These are the same as gas laws and apply to dilute solutions which occur in the living body.
VALUE OSMOS IN BIOLOGICAL PROCESSES
The blood, lymph and also all intercellular lymphs alive organisms is by aqueous solutions of moleculas and ions of many matters – organic and mineral. These solutions have definite osmotic pressure. So, the osmotic pressure of a blood of the person is value a constant and equally 7,4 105 – 7,8 105 Pa. Such high value osmotic pressure in a blood is conditioned by availability in her of a plenty of ions. High-molecular connection, mainly, proteins (albumines, the globulins), introduce 0,5 % common osmotic pressure of a blood. This part of osmotic pressure of a blood call oncotical as pressure, the value which one is equal 3,5-3,9 kPa. Oncotical pressure has large value for alive organisms. At a decrease oncotical of pressure the water goes in the party by high pressure – in a tissue, producing so called oncotical edemas of a hypodermic fat.
The osmotic pressure of a blood of the person is responded osmomolar concentration Dissoluble in plasma of matters, which one equal 0,287 – 0,0303 mol / liter.
Solutions with osmotic pressure, which is equal osmotic pressure of standard solution, is called isotonic. The solutions with osmotic by pressure are called as maximum for standard, hypertonic, and solutions with the lowest osmotic pressure hypotonic. In medical practice isotonic call solutions with osmotic pressure equal to osmotic pressure of a blood plasma. Such solution is 0, 89 % solution of sodium salt, and also 4,5 -5 % solution of a glucose. The isoosmotic solutions can be entered into an organism of the person in plenties. The hypertonic salt solutions enter in an person’s organism only in small amounts. At the introducing of a plenty hypertonic of solution the erythrocytes owing to loss of water decrease in volument and shrivel. Such phenomenon is called as a plasmolysis.
Isosmotic, isotonic, hyposmotic, hypotonic, hyperosmot1c and hypertonic solutions
– Isoosmotic solutions are those which have the same osmotic pressure as standard solution (for human body blood plasma); 0.15 molar or about 0.90 % NaC1 solution in water is isosmotic with the human blood plasma. If human red blood cells are placed in this solution, they remain intact and retain their original shape and volume. 0.90% NaC1 solution is therefore isosmotic as well as isotonic with red blood cells because in this case0the amount of water entering the cells is equal to that leaving them; thus there is no net gain or loss of water by the cells.
If а solution of NaCl more concentrated than 0.90 % is used to suspend the human or other mammalian red blood cells, water will leave the cells and the cells shrink and become crenated. Such solutions are called hypertonic. On the other hand, if red blood cells are suspended in hypotonic solutions which have less than 0.90 % NaC1, then water will enter the cells making them swollen and if the solution is very dilute the cells will rupture releasing their hemoglobin in the solution. The rupture of red blood cells is called hemolysis. Frog’s blood plasma is isotonic with about 0.6% NaCl solution.
It should however be noted that osmosis and tonicity are different. А hyperosmotic solution is not necessarily а hypertonic solution. Osmolarity is а function of the number of solute particles in solution while tonicity is а function of how well а given solute causes osmosis across а cell membrane. Suppose we suspend the RBCs in two solutions of different solutes equally hyperosmolar as compared to the RBC interior, to one of which the RBC membrane is impermeable but is permeable to the other. Result will be that in the first case the outside medium of the BBCs will remain hyperosmotic and water will flow out of the RBCs. Thus this solution is both hyperosmotic as well as hypertonic. In the second case some solute particles will enter the cell interior from outside, raising its osmotic pressure and the cells will not lose water. This second type of solution is therefore hyperosmotic but not hypertonic. In the same way а solution may be hyposmotic but not hypotonic.
Cell contains а fluid (cell sap) and its wall is composed of а living cytoplasmic membrane which is semi-permeable and is responsible for the phenomenon of osmosis in living organisms. If such а cell comes in contact with water or some dilute solution, the osmotic pressure of which is less than that of cell sap present in the cell, there will be а tendency of water to enter into the cell through the cell wall. The pressure developed inside the cell due to the inflow of water into it is called turgor. On the other hand, if the cell comes in contact with а solution of higher osmotic pressure, the cell would shrink due to going out of water from the cell through the cell wall. This shrinking of the cell is called plasmolysis.
Osmotic pressure creates some critical problems for living organisms. Cells typically contain fairly high concentrations of solutes, that is, small organic molecules and ionic salts, as well as lower concentrations of macromolecules. If cells are placed in а solution that has an equal concentration of solute, there will be no net movement of water in either direction. Such solutions are called isotonic. For example, red blood cells are isotonic to а 0.9% NaCI solution. When cells are placed in а solution with а lower solute concentration (i.е., а hypotonic solution), water will move into the cells. Red blood cells, for example, will swell and rupture in а process called hemolysis when they are immersed in pure water. In hypertonic solutions, those with higher solute concentrations, cells shrivel because there is а net movement of water out of the cell. The shrinkage of red blood cells in hypertonic solution (е.g., а 3% NaCI solution) is referred to as crenation.
Because of their relatively low cellular concentration macromolecules have little direct effect on cellular osmolarity. However, macromolecules such as the proteins contain а large number of ionizable groups. The large number of ions of opposite charge that are attracted to these groups have а substantial effect on intracellular osmolarity. Unlike most ions proteins are unable to penetrate cell membranes. (Cell membranes are not, strictly speaking, osmotic membranes, since they allow the passage of various ions, nutrients, and waste products. The term dialyzing membrane gives а more accurate description of their function.) As а result, at equilibrium the concentrations for each ionic species will not be the same on both sides of а cell’s plasma membrane. Instead, the intracellular concentrations of inorganic ions will be higher than that found outside the cell. There are several consequences of this phenomenon, called the Donnan effect:
1. а constant tendency toward cellular swelling because of water entry due to osmotic pressure,
2. the establishment of an electrical gradient called а membrane potential.
Because of the Donnan effect, cells must constantly regulate their osmolarity. Living organisms use several strategies to accomplish this goal. Many cells, for example, animal and bacterial cells, pump out certain inorganic ions such as Na+. This process, which requires а substantial proportion of cellular energy, maintains cell volume within acceptable limits. Several species, such as some protozoa and algae, periodically expel water from special contractile vacuoles. Since plant cells have rigid cell walls, plants use the Donnan effect to create an internal hydrostatic pressure called turgor pressure. This process is the driving force in cellular growth and expansion. It is also responsible for the rigidity of many plant structures.
Vapor-pressure lowering.
Shows two vapor-pressure curves, one for a pure solvent and one for its solution. The vertical distance between the two curves shows the magnitude of the vapor-pressure lowering at each temperature.
Raoult’s law. The relationship between vapor-pressure lowering and concentration in an ideal solution is stated in Raoult’s law.
Raoult’s Law: The partial vapor pressure of a component in liquid solution is propotional to the mole fraction of that component, the constant of proportionality being the vapor pressure of the pure component.
This means that a component’s vapor pressure is equal to the product of its mole fraction times its vapor pressure when pure.
Representing the solvent by the subscript 1, Raoult’s law can be written as
P1 = X1 P10
where P1 and P10 are the vapor pressure of the solution (actually, the vapor pressure of the solvent in the solution) and that of the pure solvent, respectively, and X1 is the mole fraction of the solvent in the solution. Note that as long as the solute is not volatile, P1 is the total vapor pressure of the solution.
P1 = (1- X2)P1
On the right-hand side of this relationship, P10 – P1 is the vapor-pressure lowering brought about by the presence of the solute is called the fractional vapor-pressure lowering, which can be seen to be equal to the mole fraction of the solute.
Boiling-point elevation.
The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure. At any temperature, the presence of a solute lowers the vapor pressure of a liquid, and so in order to cause a solution to boil it is necessary to raise its temperature above the boiling point of the pure solvent.
Because it is a colligative property, vapor-pressure lowering in dilute solutions depends on the concentration of solute particles but not on their identity. Therefore, we anticipate a similar relationship between boiling-point elevation and solute concentration. It can be shown that in dilute solutions the boiling-point elevation is proportional to the molality of the solute particles. (As before, we assume that the solute is not volatile.) In other words, if DTb, represents the boiling-point elevation, then:
DTb = Kbm:
Where m is the molality of the solute and Kb, is a proportionality constant known as the molal boiling-point elevation constant.
Freezing-point depression.
The phenomenon of boiling-point elevation occurs because the presence of a solute lowers the escaping tendency of the solvent. Therefore, in order to cause a solution to boil, it is necessary to raise its temperature above the boiling point of the pure solvent. Escaping tendency means tendency for molecules to escape to any other phase, however. Consequently, in order to cause solvent molecules to freeze out of a solution, the solution must be cooled to a temperature lower than the freezing point of the pure solvent so as to compensate for the decreased escaping tendency of its molecules. The relationship between freezing-point depression and molality in dilute solutions is a direct proportionality and is similar to that between boiling-point elevation and molality:
DTf= Kfm
Where: m – molality of solute; Kf – molal freezing-point depression constant freezing-point depression.
