Download 01.Coligative properties of biological liquids. Bases of titrimetric

LECTURE 1
THEME: Coligative properties of biological
liquids. Bases of titrimetric (volumetric) analysis.
Complex compound in biological systems.
ass. prof. Dmukhalska Ye.B. prepared
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 Raoult’s law
6. Collogative properties
7.
• A solution is a homogeneous
mixture of two or more substances
whose composition can be varied
within certain limits
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 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 SOLUTION
1. Depending upon the total components
present in the solution:
a) Binary solution (two components)
b) Ternary solution (three components)
c) Quaternary solution (four components)…..etc.
2. Depending upon the ability of the dissolution
some quantity of the solute in the solvent:
a) Saturated solution
b) 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 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 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 percentage
The 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. Molarity
It 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
n
m
CM 

V MV
n solute
m solute
CM 

v solution M soluteVsolution
3. Molality
It 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 kg
or
(m)
= Moles of solute * 1000/Weight of solvent in gram
The unit of Molality is m or mol/kg
n solute
msolute
Cm 

msolvent M solutemsolvent
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. It’s denoted by N or
(N) = Number of gram equivalents of solute/Volume of
solution in litres
or
(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 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. It’s denoted by X. Let suppose that solution contains
moles of solute and
moles of the solvent. Then
Vapour pressure and Raoult’s 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
1. 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 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.
Vapour pressure of solution
Vapour pressure of solution
The vapour pressure of solution is found to be less than that of
the pure solvent.
Raoult’s 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
Raoult’s law for solutions containing non-volatile
solutes
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 pressure
2. 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
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 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
Determination of Molar mass
Osmotic pressure
OSMOSIS. It is the movement of water across a semipermeable 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.
Difference between osmosis and diffusion
Osmotic pressure depends upon the
molar concentration of solution
Van’t Hoff observed that for dilute solutions, the
osmotic pressure is given as:
Determination of Molar Mass from
Osmotic Pressure
Conditions for getting accurate value of molar mass
1. The solute must be non-volatile.
2. The solution must be dilute, concentration of the
solute in the solution should not be more than 5 %
3. The solute should not undergo either dissociation or
association in the solution.
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
• The effect of hypertonic and hypotonic solutions
on animal cells.
• (а) Hypertonic solutions cause cells to shrink
(crenation) - plasmolysis;
• (b) hypotonic solutions cause cell rupture hemolysis;
• (c) isotonic solutions cause no changes in cell
volume.
• 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.
Overview of Titrimetry:
• Titrimetric methods are classified into four
groups based on the type of reaction involved.
• These groups are acid–base titrations, in which
an acidic or basic titrant reacts with an analyte
that is a base or an acid; complexometric
titrations involving a metal–ligand
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..
Typical instrumentation for performing
an
automatic titration.
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 titrant’s 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.
Equipment for Measuring Volume
• Analytical chemists use a variety of glassware to
measure volume: beaker; graduated
cylinder;volumetric flask; pipet; dropping pipet.
• 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 flask’s calibration mark is made
using a dropping pipet.
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
(a)
(b)
(c)
(d)
Common types of pipets and syringes: (a) transfer pipet; (b) measuring pipet;
(c) digital pipet; (d) syringe.
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 titrations
• Based on acid-base reactions
• The earliest acid–base titrations involved the
determination of the acidity or alkalinity of solutions,
and the purity of carbonates and alkaline earth oxides.
Before 1800, acid–base 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.
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 1:1
complexes with metal ions. The most widely used of these new
ligands was ethylenediaminetetraacetic acid, EDTA, which
forms strong 1:1 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 metal–
ligand 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 1:1 stoichiometry.
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
• K = [Pb2+][Cl–]2 = 1.7.10–5
Titrations Based on Redox Reactions
• Redox titrations were introduced shortly after the
development of acid–base
• 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.
Thank you for attention