Chemistry

2. Organic reagents are used in following quantitative
analysis
a) Gravimetric analysis
b) Volumetric analysis
c) Spectrophotometric analysis
d) Chromatographic analysis

3. ‘Gravi’ means high molecular weight insoluble specie
‘meter’ to measure.
Process of isolating and weighing a definite compound
of an element in pure form.
Then weight may be calculated from knowledge of
molecular formula of compound an atomic weight of
constituent element.

4.  Preparation of solution containing known weight of
sample
 Separation of desired constituent
 Weighing isolated constituent
 Computation of the amount of particular constituent
in sample from isolated weight of substance

5. I. Physical gravimetry involves physical separation
based on volatility and particle size
II. Thermogravimetry involves heating of sample and
recording of changes in mass of sample
III. Precpitative gravimetric analysis involves
chemical precipitation of an analyte
IV. Electrodeposition involves electrochemical
reduction of metal ions at cathode and simultaneous
deposition of ions on cathode

6. Analytical technique that uses a precipitation reaction
to separate ion from a solution the chemical that is
added to cause precipitation is called the precipitant.
Technique uses the formation and mass of precipitate.
Co-precpitation
Simultaneous precipitation of normally soluble component
with a macro-component from same solution by formation
of mixed crystal, by adsorption, occlusion, or mechanical
entrapment.

7.  Precipitation should be carried out in dilute solution
 Reagent should be mixed slowly and constant stirring
 Crystalline precipitate should be digested slowly for as
long as possible, preferably overnight
 Precipitation I effected in hot solutions, solutions
should be heated to just below boiling point

8. Gravimetric precipitating agents should react
specifically or at selectively with analytes. Ideal
precipitating reagent would react with analyte to give a
product that is;
 Easily filtered and washed
 Non-reactive with atmosphere
 Of known chemical composition after it is dried or if
necessary ignited
 Low solubility that no loss of analytes occurs

9. Advantages
 High molecular complex
is heated
 Low concentration of
metal in solution can be
determined
 Precipitates obtained are
coarse and bulky
 There is a disadvantage
of contamination
resulting in positive error
in case of selective
organic reagents
Disadvantages

10. Organic matters can be used in volumetric analysis as
 Indicator
 Titrant
 Masking and demasking agent
Indicators organic reagent
Organic reagents which show sharp change in a reaction
at end point of reaction are called indicators. They
show completion of reaction by a color change.

11. 1. Redox indicators | Organic dyes which undergo a
reversible change in color on oxidation or reduction
2. Acid base indicator | They are weak organic acids
or bases
3. Precipitation indicators | They react with one of
reactant at end point to form colored precipitant
4. Complex indicators | They are used in
complexometric reactions. They act as Lewis base
and metal ions act as Lewis acid

12. Complex formed in such titration have very low
solubility and these can be easily applied for complex
metric. Disodium salt of EDTA is used instead of
tetrasodium salt as it cause metal hydroxide
precipitation. Salt of EDTA is used as it is soluble in
water.

13.  Direct EDTA titration | In these titration metal ion
solution is buffered at pH=10. auxiliary complex are
used and concentration of metal is determined by
change in color of indicator
 Indirect EDTA titration | In this many metal ion
cannot be directly titrated because: no sharp edges,
reaction is very slow. An excess EDTA solution is
added in sample. Resulting solution is buffered to
decrease pH and complexing indicator is added in
excess of EDTA and back titrated with standard
metal ion solution

14.  Substitution or replacement | Titration used when
metal ion don’t react unsatisfactory with metal ion or
for those ions which form more stable complex than
those of Ca2+, mg2+
 Alkalimetry or acid base | Complex formation
reaction explains that proton are liberated from
sodium edetate leading to formation of acid. Acid
that is formed can be titrated against alkali but in
un-buffered solution

15.  Masking agents are those which prevent interfering
ion from reaction without physical separation
 These reagents form complexes with interfering ion
which are more stable then complexes formed with
ind. & EDTA
 De-masking agents are those which make substances
reverse back to its ability to take part in reaction

16. 1. Organic reagents giving water soluble complexes
Solubility of complexes depends upon metal complex
charge; it should be cationic or anionic. Organic
reagents ethylene diamine, ortho-phenanthroline
2. Organic reagents giving water insoluble
complexes
Form complex by disconnection of proton from neutral
complexes which are insoluble in water but soluble
in non-polar organic solvents.