THEME: Coligative properties of biological liquids. Bases of titrimetric (volumetric) analysis. Complex compound in biological systems.

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LECTURE 1
THEME Coligative properties of biological
liquids. Bases of titrimetric (volumetric)
analysis. Complex compound in biological systems.
ass. prof. Dmukhalska Ye.B. prepared
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PLAN 1. The main concepts of solutions 2. Types
of solutions 3. Heat effect of a dissolution 4.
Methods for expressing the concentration of a
solution 5. Vapour pressure and Raoults law 6.
Collogative properties 7.
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• A solution is a homogeneous mixture of two or
  more substances whose composition can be varied
  within certain limits

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The substances making up the solutions are called
components

• 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 doesnt
  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

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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 SOLUTION
• 1. Depending upon the total components present in
  the solution
• Binary solution (two components)
• Ternary solution (three components)
• Quaternary solution (four components)..etc.
• 2. Depending upon the ability of the dissolution
  some quantity of the solute in the solvent
• Saturated solution
• Not saturated solution

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

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• 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 classified
• such 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 components solubility in
  liquid solutions (which are themselves liquids),
  these mixtures may be classified into the
  following three types
• The two components are completely miscible (ethyl
  alcohol in water)
• The two components are almost immiscible (oil and
  water, benzene and water)
• 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 Raoults law.
• 2) Non-ideal solutions

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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.
• Mass percentage or volume percentage
• The mass percentage of a component in a given
  solution is the mass of the com ponent per 100 g
  of the solution.

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• 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

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2. Molarity It is the number of moles of the
solute dissolved per litre of the solution. Its
represented as M or
(?) Moles of solute / Volume of
solution in litres or (?) Mass
of component A/ Molar mass of A Volume of
solution in litres The unit of molarity is
mol/L, 1L 1000 ml
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3. Molality It is the number of moles of the
solute dissolved per 1000 g (or 1 kg) of the
solvent. Its denoted by m or (m)
Moles of solute/Weight of solvent in kg or (m)
Moles of solute 1000/Weight of solvent
in gram The unit of Molality is m or mol/kg
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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 temperature

• 4. Normality
• It is the number of gram equivalents of the
  solute dissolved per litre of the solution. Its
  denoted by N or
• Number of gram equivalents of solute/Volume
  of solution in litres
• or
• 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

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Relationship between Normality and Molarity of
Solutions Normality Molarity Molar
mass/Equivalent mass 5. Mole fraction It is the
ratio of number of moles of one component to the
total number of moles (solute and solven) present
in the solution. Its denoted by X. Let suppose
that solution contains moles of solute and
moles of the solvent. Then
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• Vapour pressure and Raoults law
• The pressure exerted by the vapours above the
  liqud surface in equilibrium with the liquid at a
  given temperature is called vapour pressure
• The vapour pressure of a liquid depends upon
• Nature of the liquid. The liquid, which have
  weaker intermolecular forces, tend to escape
  readily into vapour phase and therefore, have
  greater vapour pressure.
• 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.

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The process of evaporation in a closed container
will proceed until 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 pressure of that vapor (usually expressed in
mmHg) is called the saturated vapor pressure.
Since the molecular kinetic energy is greater at
higher temperature, more molecules can escape the
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
partial pressure along with the other
constituents of the air. The temperature at which
the vapor pressure is equal to the atmospheric
pressure is called the boiling point.
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Vapour pressure of solution
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Vapour pressure of solution The vapour pressure
of solution is found to be less than that of the
pure solvent. Raoults law for Binary solutions
of volatile liquids At 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
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Raoults law for solutions containing
non-volatile solutes

• Vapour pressure of the solutionVapour 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
  Raolts 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
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Collogative properties

• The dilute solutions of non-volatile solutes
  exhibit certain characteristic properties which
  dont 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
• Relative lowering in vapour pressure
• Elevation in boiling point
• 3. Depression in freezing point
• 4. Osmotic pressure
• This mean that if two solutions contain equal
  number of solute particles of A and B then the
  two solutions will have same colligative
  properties

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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

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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

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Depression in freezing point

• The freezing point is the temperature a which the
  solid and the liquid states of the substance have
  the same vapour pressure. The freezing point of
  the solution is always lower than that of the
  pure solvent.

where is the molal depression constant or
molal cryoscopic constant
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Determination of Molar mass
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Osmotic pressure
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OSMOSIS. It is the movement of water across a
semi-permeable membrane from an area of high
water potential (low solute concentration) to an
area of low water potential (high solute
concentration). It is a physical process in which
a solvent moves, without input of energy, across
a semi-permeable membrane (permeable to the
solvent, but not the solute) separating two
solutions of different concentrations

• or
• Osmosis is the phenomenon of the flow of solvent
  through a semi-permeable membrane from pure
  solvent to the solution.
• Osmosis can also take place between the solutions
  of different concentrations. In such cases, the
  solvent molecules move from the solution of low
  solute concentration to that of higher solute
  concentration.

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Difference between osmosis and diffusion
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Osmotic pressure depends upon the molar
concentration of solution

• Vant Hoff observed that for dilute solutions,
  the osmotic pressure is given as

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Determination of Molar Mass from Osmotic Pressure

• Conditions for getting accurate value of molar
  mass
• The solute must be non-volatile.
• The solution must be dilute, concentration of the
  solute in the solution should not be more than 5
  
• The solute should not undergo either dissociation
  or association in the solution.

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If two solutions have same osmotic pressure are
called isotonic solutions or isoosmotic solutions

• If a solution has more osmotic pressure than some
  other solutrion , it is called hypertonic
• On the other hand, a solution having less osmosis
  pressure than the other solution is called
  hypotonic
• To note that a 0,9 solution of sodium chlorine
  (known as saline water) is isotonic with human
  blood corpuscles. In this solution, the
  corpuscles neither swell nor shrink. Therefore,
  the medicines are mixed with saline water before
  being injected into the veins.
• 5 NaCl solution is hypertonic solution and when
  red blood cells are placed in this solution,
  water comes out of the cells and they shrink
• On the other hand, when red blood cells are
  placed in distilled water (hypotonic solution),
  water flows into the cells and they swell or burst

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• The effect of hypertonic and hypotonic solutions
  on animal cells.
• (?) Hypertonic solutions cause cells to shrink
  (crenation) - plasmolysis
• (b) hypotonic solutions cause cell rupture -
  hemolysis
• (c) isotonic solutions cause no changes in cell
  volume.

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

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Overview of Titrimetry

• Titrimetric methods are classified into four
  groups based on the type of reaction involved.
• These groups are acidbase titrations, in which
  an acidic or basic titrant reacts with an analyte
  that is a base or an acid complexometric
  titrations involving a metalligand complexation
  reaction redox titrations, where the titrant is
  an oxidizing or reducing agent and precipitation
  titrations, in which the analyte and titrant
  react to form a precipitate..

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Typical instrumentation for performing
anautomatic titration.
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Equivalence Points and End Points

• For a titration to be accurate we must add a
  stoichiometrically equivalent amount of titrant
  to a solution containing the analyte. We call
  this stoichiometric mixture the equivalence
  point. Unlike precipitation gravimetry, where the
  precipitant is added in excess, determining the
  exact volume of titrant needed to reach the
  equivalence point is essential. The product of
  the equivalence point volume, Veq, and the
  titrants concentration, CT, gives the moles of
  titrant reacting with the analyte.
• Moles titrant Veq . CT
• Knowing the stoichiometry of the titration
  reaction, we can calculate the moles of analyte.
  Unfortunately, in most titrations we usually have
  no obvious indication that the equivalence point
  has been reached. Instead, we stop adding titrant
  when we reach an end point of our choosing. 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
  as indicators.

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Equipment for Measuring Volume

• Analytical chemists use a variety of glassware to
  measure volume beaker graduated
  cylindervolumetric flask pipet dropping pipet.

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• Beakers, dropping pipets, and graduated cylinders
  are used to measure volumes approximately,
  typically with errors of several percent.
• Pipets and volumetric flasks provide a more
  accurate means for measuring volume.
• Volumetric flask contains a solution, it is
  useful in preparing solutions with exact
  concentrations. The reagent is transferred to the
  volumetric flask, and enough solvent is added to
  dissolve the reagent. After the reagent is
  dissolved, additional solvent is added in several
  portions, mixing the solution after each
  addition. The final adjustment of volume to the
  flasks calibration mark is made using a dropping
  pipet.

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Pipets

• A pipet is used to deliver a specified volume of
  solution. Several different
• styles of pipets are available. Transfer pipets
  provide the most accurate
• means for delivering a known volume of solution
  their volume error is similar to
• that from an equivalent volumetric flask

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(a) (b)
(c) (d)
Common types of pipets and syringes (a) transfer
pipet (b) measuring pipet (c) digital pipet
(d) syringe.
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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 liquids level
exactly at the calibration mark. The liquids top
surface is curved into a meniscus, the bottom of
which should be exactly even with the glasswares
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.
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Acid-base titrations

• Based on acid-base reactions
• The earliest acidbase titrations involved the
  determination of the acidity or alkalinity of
  solutions, and the purity of carbonates and
  alkaline earth oxides. Before 1800, acidbase
  titrations were conducted using H2SO4, HCl, and
  HNO3 as acidic titrants, and K2CO3 and Na2CO3 as
  basic titrants. End points were determined using
  visual indicators such as litmus, which is red in
  acidic solutions and blue in basic solutions, or
  by observing the cessation of CO2 effervescence
  when neutralizing CO32. The accuracy of an
  acid-base titration was limited by the usefulness
  of the indicator and by the lack of a strong base
  titrant for the analysis of weak acids.

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Titrations Based on Complexation Reactions

• The earliest titrimetric applications involving
  metal-ligand complexation The use of a
  monodentate ligand, such as Cl and CN, however,
  limited the utility of complexation titrations to
  those metals that formed only a single stable
  complex.
• The utility of complexation titrations improved
  following the introduction by Schwarzenbach, in
  1945, of aminocarboxylic acids as multidentate
  ligands capable of forming stable 11 complexes
  with metal ions. The most widely used of these
  new ligands was ethylenediaminetetraacetic acid,
  EDTA, which forms strong 11 complexes with many
  metal ions.
• Ethylenediaminetetraacetic acid, or EDTA, is an
  aminocarboxylic acid. 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 resulting metalligand
  complex, in which EDTA forms a cage-like
  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-EDTA complexes have a 11 stoichiometry.

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Precipitation Titrations

• 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, developed at the end of
  the eighteenth century, was for the analysis of
  K2CO3 and K2SO4 in potash. Calcium nitrate,
  Ca(NO3)2, was used as a titrant, forming a
  precipitate of CaCO3 and CaSO4. The end point was
  signaled by noting when the addition of titrant
  ceased to generate additional precipitate. The
  importance of precipitation titrimetry as an
  analytical method reached its zenith in the
  nineteenth century when several methods were
  developed for determining Ag and halide ions.
• Pb2(aq) 2Cl(aq) PbCl2(s)
• In the equilibrium treatment of precipitation,
  however, the reverse reaction describing the
  dissolution of the precipitate is more frequently
  encountered.
• PbCl2(s) Pb2(aq) 2Cl(aq)
• The equilibrium constant for this reaction is
  called the solubility product, Ksp, and is given
  as
• Ksp Pb2Cl2 1.7.105

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Titrations Based on Redox Reactions

• Redox titrations were introduced shortly after
  the development of acidbase
• titrimetry.
• Since titrants in a reduced state are susceptible
  to air oxidation, most redox titrations are
  carried out using an oxidizing agent as the
  titrant. The choice of which of several common
  oxidizing titrants is best for a particular
  analysis depends on the ease with which the
  analyte can be oxidized. Analytes that are strong
  reducing agents can be successfully titrated with
  a relatively weak oxidizing titrant, whereas a
  strong oxidizing titrant is required for the
  analysis of analytes that are weak reducing
  agents.

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Thank you for attention