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LECTURE 3
CHAPTER 5: CLASSICAL METHODS OF
ANALYTICAL CHEMISTRY: TITRIMETRIC
METHODS OF ANALYSIS
CO4: ABILITY TO DIFFERENTIATE VARIOUS
USED OF COMPLEXATION, REDOX AND
PRECIPITATION BASED TITRATION AND TO
CALCULATE CONCENTRATION OF
ANALYTES USING THE RESPECTIVE
TITRIMETRIC METHODS.
What is titrimetry?
• Any method in which volume is the signal.
Also known as volumetric method.
Terminology:
Titrant:
Equivalence point:
End point:
Indicator:
Type of Titrimetric Method
1.
2.
3.
4.
Classified into four groups based on type
of reaction involve;
Acid-base titrations (has been covered
by Pn. Alina)
Complexometric titrations
Redox titrations
Precipitation titrations
Assignment
• Group 10
• Explain different types of reactions
involved in titrimetry.
- Refer to page 139 to 147 in Harvey, D.
- Prepare assignment in powerpoint and
printed form
- From now on all groups have to do the
same thing.
Complexometric Titrations
• In this titration, the titrant is a complexing
agent and forms water-soluble complex
with the analyte which is a metal ion. The
titrant is often a chelating agent.
Terminology
1. Complex ions: A complex ion is a
polyatomic charged aggregate consisting
of a positively charged metal ion
combined with either a neutral or
negatively charged chemical species
called ligand.
It is a complex ion that has a metal ion at
its centre with a number of other
molecules or ions attached to it by coordinate bonds.
….Terminology
2. Ligands
- They are neutral or negatively charged
species (molecules or ions) containing
lone pairs electron that can be donated to
metal ion. All ligands are electron donors.
- Classified as uni/monodentate, bidentate
or multidentate according to the number of
bonding sites (lone pair electrons) that
they have.
….Terminology
3. Chelates
A chelate is a complex ion that involves ligands
with two or more bonding sites forming a ring
structure complex
4. Chelating agent
A substance whose molecules can form several
bonds to single metal ion. In other words, a
chelating agent is a multidentate ligand
The complex is formed when
1. The central atom accepts an electron
pair from one or more ligands.
2. The ligand possesses at least one
electron pair to donate.
3. The bonding (coordinate covalent
bonding) occurs.
The EDTA ligand
• EDTA = Ethylenediaminetetraacetate
• A Lewis acid
• Has six bonding sites (the four carboxylate
groups and the two amino groups
providing six lone pairs electrons)
• Metal-ligand complex forms a cage-like
structure around the metal ion.
• It is a very stable complex
• All metal-EDTA complexes have a 1:1
stoichiometry
EDTA-Titration
Mn+ + Y4-  MY(n-4)+
Ag+ + Y4Al3+ + Y4-
AgY3AlY-
Indicator in EDTA titrations
1. Eriochrome Black T (EBT)- a typical
metal indicator
- Mln- + HY3MY3- + Hln(grape-red)
(blue)
The indicator form grape-red complex with
the metal ion
The first slight excess of EDTA will turn the
solution to blue due to the color of free
(uncomplexed) indicator
- Disadvantage of EBT is that the indicator
solution decompose slowly on standing
2. Calmagite
Similar in structure to Eriochrome Black, but
does not decompose as easily. Similar
color behavior to Eriochrome Black.
EDTA-Application
Water hardness determination
EDTA titrations are routinely used to
determine water hardness in lab. In this
reaction, the EDTA ligand will react with the
minerals present in the water (mainly
calcium and magnesium carbonates,
sulfates, etc.)
Water hardness
• Hard water is water that has a high mineral
content. Hard water usually consists of calcium
(Ca2+), magnesium (Mg2+) ions, and possibbly
other dissolved compounds such as
bicarbonates and sulfates.
• The mineral ions along with other metal ions
such as Fe3+ and Pb2+ can be removed from
hard water by the addition of EDTA
Other EDTA Application
1. Food industry
EDTA is used as a stabilizing agent in the
food industry
- EDTA deactivates enzymes (that contain
metal) responsible for food spoilage by
removing the metal ions from them and
forming stable chelates with them.
3. Medical
i) As an anticoagulant for stored blood in
blood banks; it prevents coagulant by
sequestering the calcium ions required
for clotting.
ii) As an antidote for lead poisoning,
calcium disodium EDTA exchanges its
chelated calcium for lead, and the
resulting lead chelate is rapidly excreted
in the urine.
Calculation-example 9.8
Solution:
1. Remember:- stoichiometry for the
titration involving EDTA is always 1:1
moles EDTA = moles Ca2+
equation involve/use: M1V1 = M2V2
1 = EDTA
2 = Ca2+
have to find the molarity, M = molarity
M = moles CaCO3 = g CaCO3
V flask
FW CaCO3 X V flask
= 0.4071 g
100.09 g/mol X 0.50 L
= 8.135 x 10-3 M Ca2+
MEDTA = MCa VCa
VEDTA
= (8.135 x 10-3 M)(50.0 mL)
42.63 mL
= 9.541 x 10-3 M EDTA
Tutorial 6
Find solution for problems 36 and 37 in page
364.
Group 6 & 11 prepare the solution to be
presented in the class.