Transcript 01 Analytical chemistry. Chemical analysis

Lecture 1
Analytical chemistry.
Chemical analysis.
Associate prof . L.V. Vronska
Associate prof . M.M. Mykhalkiv
Outline
1. Object and task of analytical chemistry. Chemical
analysis and its varieties. The importance of
analytical chemistry in Pharmacy. Methods of
analysis, their classification.
2. Main principles in the theory of strong electrolytes.
3. The Law of Mass Action in analytical chemistry.
Main types of chemical equilibrium, which are
utilized in analytical chemistry.
4. Bronsted-Lowry theory of acids and bases.
1. Object and task of analytical
chemistry. Chemical analysis and its
varieties. The importance of
analytical chemistry in Pharmacy.
Methods of analysis, their
classification.
 Analytical chemistry – a sub-discipline of
Chemistry about methods of the analysis or
methods of reception of the information about
elementary objects.
 Analytical chemistry a sub-discipline of
Chemistry which develops theoretical basis and
methods of the chemical analysis.
Object of analytical chemistry is to define
chemical compounds in substances.
Main divisions of Analytical
Chemistry:
 The qualitative analysis: fractional and
systematic methods
 The quantitative analysis:
1. chemical methods
2. instrumental methods:
- physical methods of analysis
- physical-chemical methods of analysis
Scheme of Fractional Analysis
of Complex Mixtures
Mixture of components I, J, K, L, M groups
Aliquots identical mixtures
Components
IM
Components
IM
Components
IM
Components
IM
Components
IM
Reagent F
Component I
Components J  M
Component L
Reagent W
Reagent Q
Components I, J, K, M
Component J
Components I, K, L, M
Scheme of Systematic Path of Complex
Mixture Analysis
Mixture of substances of I, J, K, M group
Reagent A
Group I
Components I1, I2, I3
…
Mixture of substances
of groups J … M
Reagent B
Group J
Components J1, J2, J3
…
Mixture of substances
of groups K, M
Scheme of Analysis of Group J
Components J1, J2, J3, J4, J5
Reagent N
Components J1, J2
Components J3, J4, J5
Reagent Y
Reagent Z
Component J1
Component J3
Component J2
Components J4, J5
Reagent T
Component J4
Component J5
 The main goal of the qualitative analysis is
searching of elements, ions or chemical
compounds that are contained in the investigated
substance.
 The main goal of the quantitative analysis is to
define the quantity of the mixture ratio or
percentage of elements (ions) in substance.
Reactions in analytical chemistry
Specific
Selective
Specific reactions give an analytical effect only
with one individual substance.
NH4+ + OH - = NH3 + H2O.
Selective reactions give identical or similar
analytical effects with small number of ions (2-5).
HCl: Pb2+ + 2Cl- =PbCl2↓
Ag+ + Cl- =AgCl ↓
Hg22+ + 2Cl- =Hg2Cl2 ↓
•The group reagent is the reagent which will
meet the following requirements:
•It should precipitate cations virtually,
quantitatively (concentration of cations in a
solution should be less than 10-6 M);
•The precipitate should be easily dissolved in
certain reagents;
•Excess reagent should not alter determination
of those ions which remain in solution.
Tasks of analytical chemistry:
 Research methods of qualitative and quantitative
analysis of Nb, Ta, Zr, Ti, Hf, Mo, W, rare-earth
and other elements in mixture, because they are
used in the modern techniques.
 Research methods for detection and definition of
microquantities of elements, because often
physical and chemical properties of materials are
predetermined by their presence.
 Detect and Define chemical elements and
substances in the environment: soil, air, water,
plants
 Investigate the complex influence of related
substances on a life of plants, animals and people.
The Importance of analytical chemistry in
Pharmacy.
 Synthesis of drugs (synthetic or natural) is
necessarily supervised by methods of analytical
chemistry.
 Definition of period of drugs validity is based on
methods of analytical chemistry.
Chemical analysis and its
varieties:
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Elemental analysis
Function analysis
Molecular analysis
Phase analysis
Diffraction analysis
Elemental analysis is qualitative and quantitative
analysis of elements in compound clear substance
Function analysis is the analysis which answer
what functional groups are contained in
investigated substance
Methods of the molecular analysis receive the
information about substances which consist
of molecules or formular parts.
Phase analysis – detection and definition of
different phases (solid, liquid, gas), which are
contained in the investigated system.
Diffraction analysis determines the crystal lattice
structure containing atoms, molecules and
ions.
Pharmaceutical analysis is determination of
drug quality (manufactured or pharmacy
compounded)
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Pharmaceutical analysis includes:
analysis of drugs
analysis of medicinal herbs
process monitoring of drugs
toxicological analysis
judicial-chemical analysis
IUPAC Classification of analytical methods in
accordance with mass and volume of analytic
sample
Method name
Mass of sample, g
Volume of sample,
ml
1–10
10–100
Cantigramm-method
0,05–0,5
1–10
Milligramm-method
10-6–0,001
10-4–0,1
Microgramm-method
10-9–10-6
10-6–10-4
Nanogramm-method
10-12–10-9
10-10–10-7
Picogramm-method
10-12
10-10
Gramm-method
The signal which bears the information on
elementary objects, is called as an analytical
signal.
The analytical signal can be the carrier for both
qualitative and quantitative information.
Sensitivity of analytical reaction is the least
amount of substance, which can be detected with
the reagent in one drop of solution.
The sensitivity express to next correlated values:
 Limit of detection = Determined minimum (m)
– the least amount of substance, which present in
analysed solution and can be detected with the
reagent. Calculated in g. 1 g = 0,000001 g.
 Limit
of
concentration
=
Minimal
concentration (Cmin) – the least concentration of
substance in the solution which still can be
detected in small portion or volume of analysed
solution.
 Maximum of dilution (W = 1/Cmin) –
quantity (ml) of solution, containing 1 g of
the analysed substance, which can be
detected with a definite reaction (reagent).
Analytical reaction is considered more
sensitive
under
conditions
when
determined minimum and minimal
concentration of analyzed solution are low
and maximum of dilution is high.
2. Main principles of theory of
strong electrolytes.
 activity (а) – effective concentration of ions in
solution, when it reacts
a
lim
 1.
C  0 C
To calculate activity coefficients use the
following:
1. Ionic strength of solution
1
2
    C i Z i
2
where ci and zi are the concentration and charge of
the ith ion.
2. Activity coefficients for ionic solutes, depend on
the ionic strength of solution by using the
extended Debye–Hückel theory
To calculate activity coefficients use
the Debye–Hückel equation
 if   0,01
lg f i  0,512Z i2  ,
 if   0,1
2
0,512Z i 
lg f i  
,
 if   1,0
1 
2
0,512Z i 
lg f i  
 0,1 Z i2  ,
1 
Experimentally is possible to find
only the Mean activity coefficient:
 for binary electrolyte AB
f
f A  fB ,
 for electrolyte structure AmBn
f 
mn
f Am  f Bn ,
Mean activity coefficient may be
calculated theoretically by using
Debye–Hückel equation:
 if   0,01
lg f   0,512Z A Z B  ,
 if   0,1
0,512Z A Z B 
lg f   
,
1 
 if  1,0.
0,512Z A Z B 
lg f   
 0,1Z A Z B  .
1 
For simplification of calculations of
activity coefficients use these
assumptions:
1. Activity coefficients of ions with identical
charge irrespective of ion’s radius are
approximately equal.
2. Activity coefficients of neutral parts in dilute
solutions of electrolytes equals 1.
3. Very dilute solutions of electrolytes are possible
to consider ideal.
3. The Law of Mass Action in
Analytical Chemistry.
Concentrational (real) constant of chemical
equilibrium
l
p
[C ] [ D]
K 
.
n
m
[ A] [ B]
R
nA + mB  lC +pD
p-function of constant equilibrium
pK = –lgK.
КТ – thermodynamic equilibrium constant (it
depends on temperature and pressure)
l
p
l
p
a

a
f

f
K T  Cn Dm  K R Cn Dm ;
a A  aB
f A  fB
where f – activity coefficient
We use KR, when we have real conditions
(influence of ionic strength, temperature and
pressure)
КC – conditional equilibrium constant
l
p
C

C
K C  Cn Bm ,
C A  CB
 where C – formality, is a substance’s total
concentration in solution regardless of its specific
chemical form.
c
d
c
d
T



f

f
C
D
C
D
KC  K

.
a
b
a
b
 A  B f A  f B
[ion]
 ion 
Cion
where  - parts per mol
 We use KC, when we have the following
real conditions (influence of ionic
strength, temperature and pressure,
competitive reactions)
Mass balance equation, which is simply a
statement of the conservation of matter. In a
solution of a monoprotic weak acid (base), for
example, the combined concentrations of the
conjugate weak acid (base), HA, and the
conjugate weak base (acid), A–, must equal the
weak acid’s (base’s) initial concentration, CHA.
H2S  H+ + HSHS-  H+ + S2CS = [S2–] + [HS–] + [H2S].
A charge balance equation is a statement of solution
electroneutrality.
Total positive charge from cations = total negative charge
from anions
Mathematically, the charge balance expression is expressed
as
where [Mz+]i and [Az–]j are, respectively, the concentrations
of the ith cation and the jth anion, and (z+)i and (z–)j are
the charges of the ith cation and the jth anion.
The charge balance equation for an aqueous
solution of Ca(NO3)2 is
2 [Ca2+] + [H3O+] = [OH–] + [NO3–]
Main types of chemical reactions which are
used in analytical chemistry:
 Acid-base reaction (the reaction of an acid with a
base)
CH3COOH(aq) + NH3(aq)  CH3COO–(aq) + NH4+(aq)
 A precipitation reaction occurs when two or
more soluble species combine to form an insoluble
product.
Pb2+(aq) + 2Cl–(aq)  PbCl2(s)
 reaction between the metal ion and the ligand is
typical of a complexation reaction.
Cd2+(aq) + 4(:NH3)(aq)  Cd(:NH3)42+(aq)
 redox reaction - an electron-transfer reaction.
2Fe3+(aq) + H2C2O4(aq) + 2H2O(l)  2Fe2+(aq) +
2CO2(g) + 2H3O+(aq)
4. Bronsted-Lowry theory of acids
and bases.
A substance, that dissolves in water to give an
electrically conducting solution is called an
electrolyte.
A substance, that dissolves in water to give
nonconducting or very poorly conducting
solution is called a nonelectrolyte.
According to Svante Arrhenius concept:
Acid is any substance that, when dissolved in water,
increase the concentration of hydrogen ion H+.
Base is any substance that, when dissolved in water,
increase the concentration of hydroxide ion OH–.
NaOH  Na+ + OH–
HCl  H+ + Cl–
A useful definition of acids and bases was independently introduced by Johannes Brønsted (1879–1947)
and Thomas Lowry (1874–1936) in 1923.
 acids are proton donors
 bases are proton acceptors
Acid  Base + Н+
Constant reaction of a dissociation solvent has
equation
a
a

H
Solv
Solv
2
K T HSolv 
.
2
a HSolv
Autoprotolysis constant of solvent is product
of activity lyonium and lyate
KT
HSolv  a
H 2 Solv

a
Solv  ,
Neutrality of solution determines activity of
lyonium and lyate іons:
a
H 2 Solv

a
Solv
,
pH  pSolv
 Condition of neutrality
pH  1 / 2 pK T
HSolv
рН of some solvents
Solvent
Limits рН
Solvent
Limits рН
H2SO4
0 – 3,6
C2H5OH
0 – 19,00
HCOOH
0 – 6,70
CH3– C  N
0 – 19,00
0 – 22,0
H2O
0-14
CH3COOH
0 – 14,4
liquid
ammonia
CH3OH
0 – 17,3
FMA
0 – 17,0
acetone
0 – 21,1
DMFA
0 – 18,0
The Brønsted-Lowry concept of acids and bases
has greater scope than the Arrhenius concept:
 the general description of acid-base reaction
 possibility a quantitative estimation strength of
acid and base
НА + Н2О  Н3О+ + А–
K aT 
a
H 3O

a
a HA
A
B + H2O  BH+ + OH–
a

a

T
BH
OH
Kb 
aB
Solvents:
 progenic (A species that can serve as a proton
donor)
 protophilic (A species that can serve as a
proton acceptor)
 amphiprotic (A species that can serve as both a
proton donor and a proton acceptor)
 aprotic (A species that can’t serve a proton)
proton acceptor’s properties increase 
H2SO4; CCl3COOH; CH3COOH; H2O; C2H5OH; NH3; C5H5N
proton donor’s properties increase

Thanks for your attention!