THEME: Coligative properties of biological THEME: Coligative properties of biological liquids. Bases of titrimetric (volumetric) analysis. liquids. Bases of titrimetric (volumetric) analysis.

Complex compound in biological systems.Complex compound in biological systems.

LECTURELECTURE 11

ass. prof. Dmukhalska Ye.B. preparedass. prof. Dmukhalska Ye.B. prepared

PLAN1. The main concepts of solutions2. Types of solutions3. Heat effect of a dissolution4. Methods for expressing the concentration of a solution5. Vapour pressure and Raoult’s law6. Collogative properties7.

• A solution is a homogeneous mixture of two or more substances whose composition can be varied within certain limits

The substances making up the The substances making up the solutions are called solutions are called componentscomponents

• The components of a binary solution are solute and solvent.

• Solvent is a component which is present in excess, in other words a solvent is a substance in which dissolution takes place. Solvent doesn’t change its physical state during reaction of dissolution.

• Solute is a component which is present in lesser quantity. Or solute is a substance that dissolves

In a solution, the particles are of molecular size (about 1000 pm) and the different components cannot be separated by any of the physical methods such as filtration, setting, centrifugation, etc.)

TYPES OF SOLUTION1. Depending upon the total components 1. Depending upon the total components

present in the solution:present in the solution:a) Binary solution (two components)b) Ternary solution (three components)c) Quaternary solution (four components)…..etc.2. Depending upon the ability2. Depending upon the ability of the dissolution of the dissolution

some quantity of the solute in the solvent:some quantity of the solute in the solvent:a) Saturated solutionb) Not saturated solution

3. Depending upon the physical states of the solute and solvent, the solution can be classified into the following nine type:

Out of the nine types of solutions, namely solid in liquid, liquid in liquid and gas in liquid are very common. In all these types of solutions, liquid acts as solvent.

4. According to the nature of solvent the solutions can be classifiedsuch as: a) aqueous solution – the solution in which water is a solvent;b) non- aqueous solution in which water is not the solvent (ether, benzene…)The basic rule for solubility is “like dissolves like”5. Depending upon component’s solubility in liquid solutions (which are

themselves liquids), these mixtures may be classified into the following three types:

1)The two components are completely miscible (ethyl alcohol in water)2)The two components are almost immiscible (oil and water, benzene and

water)3)The two components are partially miscible (ether and water)6. The binary solutions may be classified into two types:1) Ideal solutions. Such solutions are formed by mixing the two components

which are identical in molecular size, in structure and have almost identical intermolecular forces. In these solutions, the intermolecular interactions between the components (A-B) are of same magnitude as the intermolecular interactions in pure components ( A-A and B-B). Ideal solutions obeys Raoult’s law.

2) Non-ideal solutions

Methods for expressing the concentration of a solution

The concentration of a solution may be defined as the amount of solute present in the given quantity of the solution.

1. Mass percentage or volume percentageThe mass percentage of a component in a given solution is the

mass of the com ponent per 100 g of the solution.

• Mass concentration, titer (T) is number grams of solute (m) per one milliliter of solution (V). Or it is the ratio of the quantity grams of solute and volume solution:

T = m

V

2. MolarityIt is the number of moles of the solute dissolved per litre of the solution. It’s represented as M or

(М) = Moles of solute / Volume of solution in litres or

(М) = Mass of component A/ Molar mass of A *Volume of solution in litres The unit of molarity is mol/L, 1L = 1000 ml

MV

m

V

n CM

VM

m

v

n C

solutionsolute

solute

solution

soluteM

3. MolalityIt is the number of moles of the solute dissolved per 1000 g (or 1 kg) of the solvent. It’s denoted by m or (m) = Moles of solute/Weight of solvent in kgor(m) = Moles of solute * 1000/Weight of solvent in gramThe unit of Molality is m or mol/kg

mM

m

m

n C

solventsolute

solute

solvent

solutem

Molalty is considered better for expressing the concentration as compared to molarity because the molarity changes with temperature because of expansion of the liquid with the temperature4. NormalityIt is the number of gram equivalents of the solute dissolved per

litre of the solution. It’s denoted by N or (N) = Number of gram equivalents of solute/Volume of

solution in litresor

(N) = Number of gram equivalents of solute *1000/Volume of solution in

ml

Number of gram equivalents of solute = Mass of solute / Equivalent mass of

solute

Relationship between Normality and Molarity of SolutionsRelationship between Normality and Molarity of Solutions

Normality = Molarity * Molar mass/Equivalent massNormality = Molarity * Molar mass/Equivalent mass

5. Mole fraction5. Mole fractionIt is the ratio of number of moles of one component to the It is the ratio of number of moles of one component to the

total number of moles (solute and solven) present in the total number of moles (solute and solven) present in the solution. It’s denoted by X. Let suppose that solution contains solution. It’s denoted by X. Let suppose that solution contains

moles of solute and moles of the solvent. Then

Vapour pressure and Raoult’s lawThe pressure exerted by the vapours above the liqud

surface in equilibrium with the liquid at a given temperature is called vapour pressurevapour pressure

The vapour pressure of a liquid depends upon1.Nature of the liquid. The liquid, which have weaker

intermolecular forces, tend to escape readily into vapour phase and therefore, have greater vapour pressure.

2.Temperature. The vapour pressure of a liquid increases with increase in temperature. This is due to the fact that with increase in temperature, more molecules will have large kinetic energies. Therefore, larger number of molecules will escape from the surface of the liquid to the vapour phase resulting higher vapour pressure.

The process of The process of evaporationevaporation in a closed container will proceed until in a closed container will proceed until there are as many molecules returning to the liquid as there are there are as many molecules returning to the liquid as there are escaping. At this point the vapor is said to be saturated, and the escaping. At this point the vapor is said to be saturated, and the pressure of that vapor (usually expressed in mmHg) is called the pressure of that vapor (usually expressed in mmHg) is called the saturated saturated vapor pressurevapor pressure. Since the molecular kinetic energy is . Since the molecular kinetic energy is greater at higher greater at higher temperaturetemperature, more molecules can escape the , more molecules can escape the surface and the saturated vapor pressure is correspondingly higher. surface and the saturated vapor pressure is correspondingly higher. If the liquid is open to the air, then the vapor pressure is seen as a If the liquid is open to the air, then the vapor pressure is seen as a partial pressure along with the other constituents of the partial pressure along with the other constituents of the airair. The . The temperature at which the vapor pressure is equal to the temperature at which the vapor pressure is equal to the atmosphericatmospheric pressurepressure is called the is called the boilingboiling pointpoint..

Vapour pressure of solution

Vapour pressure of solution

The vapour pressure of solution is found to be less than that of The vapour pressure of solution is found to be less than that of the pure solvent.the pure solvent.

Raoult’s law for Binary solutions of volatile liquidsRaoult’s law for Binary solutions of volatile liquidsAt a given temperature, for a solution of volatile liquids, the

partial pressure of each component is equal to the product of the vapour pressure of the pure component and its mole fraction.

Suppose a binary solution consists of two volatile liquids A and B. If and are the partial vapour pressure of the two lquids and a are their mole fractions in solution, then

Raoult’s law for solutions containing non-volatile Raoult’s law for solutions containing non-volatile solutessolutes

Vapour pressure of the solution=Vapour pressure of the solvent in the solution

If is the vapour pressure of the solvent over a solution containing non-volatile solute and is its mole fraction then according to Raolt’s law,

or

At a given temperature , the vapour pressure of a solution containing non-volatile solute is directly proportional to the mole fraction of the solvent

Collogative properties

The dilute solutions of non-volatile solutes exhibit certain characteristic properties which don’t depend upon the nature of the solute but depend only on the number of particles of the solute, on the molar concentration of the solute. These are called colligative properties. Thus

1. Relative lowering in vapour pressure2. Elevation in boiling point3. Depression in freezing point4. Osmotic pressureThis mean that if two solutions contain equal number of solute particles of

A and B then the two solutions will have same colligative properties

The relative lowering in vapour pressure of an ideal solution containing the non-volatile solute is equal to the mole fraction of the solute at a given temperature.

where A is a solvent, B is a solute

Elevation in boiling point

The boiling point of a liquid is the temperature at which its vapour pressure becomes equal to the atmospheric pressure. The boiling point of the solution is always higher than that of the pure solvent. The different in the boiling points of the solution and pure solvent is called the elevation in boiling point

It has been found out experimentally that the elevation in the boiling point of a solution is proportional to the molality concentration of the solution

where is called molal elevation constant or ebullioscopicconstant

Depression in freezing pointThe freezing point is the temperature a which the solid and The freezing point is the temperature a which the solid and

the liquid states of the substance have the same vapour the liquid states of the substance have the same vapour pressure. The freezing point of the solution is always pressure. The freezing point of the solution is always lower than that of the pure solvent.lower than that of the pure solvent.

where is the molal depression constant or molal cryoscopic constant

Determination of Determination of Molar massMolar mass

Osmotic pressure

OSMOSIS.OSMOSIS. I It is the movement of water across a semi-t is the movement of water across a semi-permeable membrane from an area of high permeable membrane from an area of high waterwater potentialpotential (low (low solutesolute concentration) to an area of low water potential concentration) to an area of low water potential (high solute concentration). It is a physical process in (high solute concentration). It is a physical process in which a solvent moves, without input of energy, across a which a solvent moves, without input of energy, across a semi-permeable membrane (permeable to the semi-permeable membrane (permeable to the solventsolvent, but , but not the solute) separating two solutions of different not the solute) separating two solutions of different concentrationsconcentrations oror

Osmosis is the phenomenon of the flow of solvent through Osmosis is the phenomenon of the flow of solvent through a semi-permeable membrane from pure solvent to the a semi-permeable membrane from pure solvent to the solution.solution.

Osmosis can also take place between the solutions of Osmosis can also take place between the solutions of different concentrations. In such cases, the solvent different concentrations. In such cases, the solvent molecules move from the solution of low solute molecules move from the solution of low solute concentration to that of higher solute concentration.concentration to that of higher solute concentration.

Difference between osmosis and diffusionDifference between osmosis and diffusion

Osmotic pressure depends Osmotic pressure depends upon the molar upon the molar

concentration of solutionconcentration of solutionVan’t Hoff observed that for dilute Van’t Hoff observed that for dilute

solutions, the osmotic pressure is solutions, the osmotic pressure is given as:given as:

Determination of Molar Mass Determination of Molar Mass from Osmotic Pressurefrom Osmotic Pressure

Conditions for getting accurate value of molar massConditions for getting accurate value of molar mass1.1. The solute must be non-volatile.The solute must be non-volatile.2.2. The solution must be dilute, concentration of the The solution must be dilute, concentration of the

solute in the solution should not be more than 5 %solute in the solution should not be more than 5 %3.3. The solute should not undergo either dissociation or The solute should not undergo either dissociation or

association in the solution.association in the solution.

If two solutions have same osmotic pressure are If two solutions have same osmotic pressure are

called called isotonic solutions or isoosmoticisotonic solutions or isoosmotic solutionssolutionsIf a solution has more osmotic pressure than some other If a solution has more osmotic pressure than some other

solutrion , it is called solutrion , it is called hypertonichypertonicOn the other hand, a solution having less osmosis pressure On the other hand, a solution having less osmosis pressure

than the other solution is called than the other solution is called hypotonichypotonicTo noteTo note that a 0,9% solution of sodium chlorine (known as that a 0,9% solution of sodium chlorine (known as

saline water) is isotonic with human blood corpuscles. In saline water) is isotonic with human blood corpuscles. In this solution, the corpuscles neither swell nor shrink. this solution, the corpuscles neither swell nor shrink. Therefore, the medicines are mixed with saline water before Therefore, the medicines are mixed with saline water before being injected into the veins.being injected into the veins.

5% NaCl solution is hypertonic solution and when red blood 5% NaCl solution is hypertonic solution and when red blood cells are placed in this solution, water comes out of the cells cells are placed in this solution, water comes out of the cells and they and they shrinkshrink

On the other hand, when red blood cells are placed in distilled On the other hand, when red blood cells are placed in distilled water (hypotonic solution), water flows into the cells and water (hypotonic solution), water flows into the cells and they they swell or burstswell or burst

• The effect of hypertonic and hypotonic The effect of hypertonic and hypotonic solutions on animal cells.solutions on animal cells.

• (а) Hypertonic solutions cause cells to (а) Hypertonic solutions cause cells to shrink (crenation) - plasmolysis;shrink (crenation) - plasmolysis;

• (b) hypotonic solutions cause cell (b) hypotonic solutions cause cell rupture - hemolysis; rupture - hemolysis;

• (c) isotonic solutions cause no (c) isotonic solutions cause no changes in cell volume.changes in cell volume.

• Titrimetry, in which we measure the volume of a Titrimetry, in which we measure the volume of a reagent reacting stoichiometrically with the reagent reacting stoichiometrically with the analyte, first appeared as an analytical method in analyte, first appeared as an analytical method in the early eighteenth century. the early eighteenth century.

Overview of Titrimetry:Overview of Titrimetry:• Titrimetric methods are classified into four Titrimetric methods are classified into four

groups based on the type of reaction involved.groups based on the type of reaction involved.• These groups are acid–base titrations, in which These groups are acid–base titrations, in which

an acidic or basic titrantan acidic or basic titrant reacts with an analyte reacts with an analyte that is a base or an acid; complexometric that is a base or an acid; complexometric titrations involving a metal–ligand titrations involving a metal–ligand complexation reaction; redox titrations, where complexation reaction; redox titrations, where the titrant is an oxidizing or reducing agent; the titrant is an oxidizing or reducing agent; and precipitation titrations, in which the and precipitation titrations, in which the analyte and titrant react to form a precipitate.analyte and titrant react to form a precipitate. ..

Typical instrumentation for performing Typical instrumentation for performing ananautomatic titration.automatic titration.

Equivalence Points and End PointsEquivalence Points and End Points• For a titration to be accurate we must add a stoichiometrically equivalent For a titration to be accurate we must add a stoichiometrically equivalent

amount of titrant to a solution containing the analyte. We call this amount of titrant to a solution containing the analyte. We call this stoichiometric mixture the stoichiometric mixture the equivalence point. equivalence point. Unlike precipitation Unlike precipitation gravimetry, where the precipitant is added in excess, determining the gravimetry, where the precipitant is added in excess, determining the exact volume of titrant needed to reach the equivalence point is essential. exact volume of titrant needed to reach the equivalence point is essential. The product of the equivalence point volume, VThe product of the equivalence point volume, Veqeq, and the titrant’s , and the titrant’s concentration, concentration, CCTT, gives the moles of titrant reacting with the analyte., gives the moles of titrant reacting with the analyte.

• Moles titrant = VMoles titrant = Veqeq . . CCTT

• Knowing the stoichiometry of the titration reaction, we can calculate the Knowing the stoichiometry of the titration reaction, we can calculate the moles of analyte. Unfortunately, in most titrations we usually have no moles of analyte. Unfortunately, in most titrations we usually have no obvious indication that the equivalence point has been reached. Instead, obvious indication that the equivalence point has been reached. Instead, we stop adding titrant when we reach an we stop adding titrant when we reach an end point end point of our choosing. of our choosing. Often this end point is indicated by a change in the color of a substance Often this end point is indicated by a change in the color of a substance added to the solution containing the analyte. Such substances are known added to the solution containing the analyte. Such substances are known as as indicators.indicators.

Equipment for Measuring Equipment for Measuring VolumeVolume

• Analytical chemists use a variety of Analytical chemists use a variety of glassware to measure volumeglassware to measure volume: : beaker; beaker; graduated cylinder;volumetric flask; graduated cylinder;volumetric flask; pipet;pipet; dropping pipet.dropping pipet.

• Beakers, dropping pipets, and graduated cylindersBeakers, dropping pipets, and graduated cylinders are are used to measure volumes approximatelyused to measure volumes approximately, , typically with typically with errors of several percent.errors of several percent.

• Pipets and volumetric flasks provide a more accurate Pipets and volumetric flasks provide a more accurate means for measuring volumemeans for measuring volume..

• VolumetricVolumetric flask contains a solution, it is useful in flask contains a solution, it is useful in preparing solutions with exact concentrations. The reagent preparing solutions with exact concentrations. The reagent is transferredis transferred to theto the volumetric flaskvolumetric flask,, and enough solvent and enough solvent isis added to dissolve the reagent. After the reagent is added to dissolve the reagent. After the reagent is dissolveddissolved,, additional solvent is added in several portions additional solvent is added in several portions, , mixing the solution after each additionmixing the solution after each addition.. The final The final adjustment of volume to the flask’s calibration mark is adjustment of volume to the flask’s calibration mark is mademade using using aa dropping dropping pipetpipet..

PipetsPipets

• A A pipet pipet is used to deliver a specified is used to deliver a specified volume of solution. Several differentvolume of solution. Several different

• styles of pipets are available. Transfer styles of pipets are available. Transfer pipets provide the most accuratepipets provide the most accurate

• means for delivering a known volume of means for delivering a known volume of solution; their volume error is similar tosolution; their volume error is similar to

• that from an equivalent volumetric flaskthat from an equivalent volumetric flask

Common types of pipets and syringes: (a) transfer pipet; (b) measuring pipet; (c) digital pipet; (d) syringe.

(a) (b) (c) (d)

Three important precautions are needed when working with pipets and volumetric flasks. First, the volume delivered by a pipet or contained by a volumetric flask assumes that the glassware is clean. Second, when filling a pipet or volumetric flask, set the liquid’s level exactly at the calibration mark. The liquid’s top surface is curved into a meniscus, the bottom of which should be exactly even with the glassware’s calibration mark.

Before using a pipet or volumetric flask you should rinse it with several small portions of the solution whose volume is being measured.

Acid-base titrationsAcid-base titrations• Based on acid-base reactionsBased on acid-base reactions• The earliest The earliest acid–base titrations acid–base titrations involved the determination involved the determination

of the acidity or alkalinity of solutions, and the purity of of the acidity or alkalinity of solutions, and the purity of carbonates and alkaline earth oxides. Before 1800, acid–base carbonates and alkaline earth oxides. Before 1800, acid–base titrations were conducted using Htitrations were conducted using H22SOSO44, HCl, and HNO, HCl, and HNO33 as as acidic titrants, and Kacidic titrants, and K22COCO33 and Na and Na22COCO33 as basic titrants. End as basic titrants. End points were determined using visual indicators such as litmus, points were determined using visual indicators such as litmus, which is red in acidic solutions and blue in basic solutions, or which is red in acidic solutions and blue in basic solutions, or by observing the cessation of COby observing the cessation of CO22 effervescence when effervescence when neutralizing COneutralizing CO33

2–2–. The accuracy of an acid-base titration was . The accuracy of an acid-base titration was limited by the usefulness of the indicator and by the lack of a limited by the usefulness of the indicator and by the lack of a strong base titrant for the analysis of weak acids.strong base titrant for the analysis of weak acids.

Titrations Based on Complexation ReactionsTitrations Based on Complexation Reactions• The earliest titrimetric applications involving metal-ligand complexation The earliest titrimetric applications involving metal-ligand complexation

The use of a monodentate ligand, such as ClThe use of a monodentate ligand, such as Cl– – and CNand CN––, however, limited , however, limited the utility of the utility of complexation titrations complexation titrations to those metals that formed only a to those metals that formed only a single stable complex.single stable complex.

• The utility of complexation titrations improved following the introduction The utility of complexation titrations improved following the introduction by Schwarzenbach, in 1945, of aminocarboxylic acids as multidentate by Schwarzenbach, in 1945, of aminocarboxylic acids as multidentate ligands capable of forming stable 1:1 complexes with metal ions. The ligands capable of forming stable 1:1 complexes with metal ions. The most widely used of these new ligands was ethylenediaminetetraacetic most widely used of these new ligands was ethylenediaminetetraacetic acid, EDTA, which forms strong 1:1 complexes with many metal ions. acid, EDTA, which forms strong 1:1 complexes with many metal ions.

• Ethylenediaminetetraacetic acid, or EDTA, is an aminocarboxylic acid. Ethylenediaminetetraacetic acid, or EDTA, is an aminocarboxylic acid. EDTA, which is a Lewis acid, has six binding sites (the four carboxylate EDTA, which is a Lewis acid, has six binding sites (the four carboxylate groups and the two amino groups), providing six pairs of electrons. The groups and the two amino groups), providing six pairs of electrons. The resulting metal–ligand complex, in which EDTA forms a cage-like resulting metal–ligand complex, in which EDTA forms a cage-like structure around the metal ion, is very stable. The actual number of structure around the metal ion, is very stable. The actual number of coordination sites depends on the size of the metal ion; however, all metal-coordination sites depends on the size of the metal ion; however, all metal-EDTA complexes have a 1:1 stoichiometry.EDTA complexes have a 1:1 stoichiometry.

Precipitation TitrationsPrecipitation Titrations• A reaction in which the analyte and titrant form an insoluble precipitate also A reaction in which the analyte and titrant form an insoluble precipitate also

can form the basis for a titration. One of the earliest precipitation titrations, can form the basis for a titration. One of the earliest precipitation titrations, developed at the end of the eighteenth century, was for the analysis of Kdeveloped at the end of the eighteenth century, was for the analysis of K22COCO33 and Kand K22SOSO44 in potash. Calcium nitrate, Ca(NO in potash. Calcium nitrate, Ca(NO33))22, was used as a titrant, forming , was used as a titrant, forming a precipitate of CaCOa precipitate of CaCO33 and CaSO and CaSO44. The end point was signaled by noting when . The end point was signaled by noting when the addition of titrant ceased to generate additional precipitate. The importance the addition of titrant ceased to generate additional precipitate. The importance of precipitation titrimetry as an analytical method reached its zenith in the of precipitation titrimetry as an analytical method reached its zenith in the nineteenth century when several methods were developed for determining Agnineteenth century when several methods were developed for determining Ag++ and halide ions.and halide ions.

• PbPb2+2+((aqaq) + 2Cl) + 2Cl––((aqaq) =PbCl) =PbCl22((ss))• In the equilibrium treatment of precipitation, however, the reverse reaction In the equilibrium treatment of precipitation, however, the reverse reaction

describing the dissolution of the precipitate is more frequently encountered.describing the dissolution of the precipitate is more frequently encountered.• PbClPbCl22((ss) = Pb) = Pb2+2+((aqaq) + 2Cl) + 2Cl––((aqaq))• The equilibrium constant for this reaction is called the The equilibrium constant for this reaction is called the solubility product, solubility product, KKsp, sp,

and is given asand is given as• KKspsp = [Pb = [Pb2+2+][Cl][Cl––]]22 = 1.7 = 1.7..1010–5 –5

Titrations Based on Redox ReactionsTitrations Based on Redox Reactions• Redox titrations Redox titrations were introduced shortly after the were introduced shortly after the

development of acid–basedevelopment of acid–base• titrimetry. titrimetry. • Since titrants in a reduced state are susceptible to air Since titrants in a reduced state are susceptible to air

oxidation, most redox titrations are carried out using an oxidation, most redox titrations are carried out using an oxidizing agent as the titrant. The choice of which of oxidizing agent as the titrant. The choice of which of several common oxidizing titrants is best for a particular several common oxidizing titrants is best for a particular analysis depends on the ease with which the analyte can be analysis depends on the ease with which the analyte can be oxidized. Analytes that are strong reducing agents can be oxidized. Analytes that are strong reducing agents can be successfully titrated with a relatively weak oxidizing successfully titrated with a relatively weak oxidizing titrant, whereas a strong oxidizing titrant is required for titrant, whereas a strong oxidizing titrant is required for the analysis of analytes that are weak reducing agents.the analysis of analytes that are weak reducing agents.

Thank you for attention