This module consists of six study units that are further divided into study sections. The study units include basic concepts, volumetry, gravimetry, surface characterization, atomic spectrometry, and separation methods. The document then provides an overview of analytical chemistry and its branches, classification of quantitative analysis methods, and learning outcomes related to volumetric analysis and titrations. [/SUMMARY]

1. THIS MODULE CONSISTS OF SIX STUDY UNITS
 Basic concepts
 Volumetry
 Gravimetry
 Surface characterisation
 Atomic spectrometry
 Separation methods
Each of these study units is sub-divided into different study sections

2. What is Analytical Chemistry????
Branches of analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of
the chemical components of natural and artificial materials
Quantitative
determines the amount of certain
components in the substance
Qualitative
gives an indication of the identity of
the chemical species in the sample
Qualitative: recognized by color, boiling point, solubility, taste

3. Classification of Quantitative Methods of Analysis
Classical methods
Gravimetric Method: mass is
measured.
Volumetric Method: volume is
measured
Instrumental Method
use an instrumental technique to
assay the amount of sample
Electro analytical
Measurement of electrical property
Spectrophotometric
Interaction of light and matter

4. Overall Learning Outcomes
• State the requirements for a titration
• Classify various volumetric methods
• Describe a titration curve
• Determine the concentrations of various analytes using
volumetric analysis

5. Volumetric analysis
• Procedures in which the volume of reagent needed to
react with an analyte is measured.
• Commonly used to determine the unknown
concentration of a known reactant.
• Volumetric analysis is often referred to as titration, a
laboratory technique in which one substance of
known concentration and volume is used to react
with another substance of unknown
concentration.

6. Common Types Of Titrations

7. Terms
• Titration : A procedure for determining the amount of some
unknown substance (the analyte ) by quantitative reaction with a
measured volume of a solution of precisely known concentration
(the titrant).
• Titrant : The substance that quantitatively reacts with the
analyte in a titration . The titrant is usually a standard solution
added carefully to the analyte until the reaction is complete.
• Indicators : organic chemicals that change colour as the pH of a
solution changes
• Direct titration : Titrant is added to the analyte until the
reaction is complete.
• Back titration : Adding a known excess of reagent to the analyte,
then, a second reagent is used to titrate the excess of the first
reagent.

8. • Equivalence point : point in a titration at which equivalent
amounts of titrant is the exact amount necessary for
stoichiometric reaction with the analyte.
• End point : the point in a titration when a physical change
occurs that is associated with the condition of chemical
equivalence.
• Titration error : The difference in volume or mass between
the equivalence point and the end point.
titration error : eT = Vep – Veq
Vep = actual volume at end point,
Veq = theoretical volume of equivalence point
Cont.

9. • Titration Curve: The plot of pH vs. volume.
• Standard solution : A solution of precisely known
concentration.
• Primary standard : An ultra-pure (99.9% purity) compound
that serves as the reference material for a titrimetric
method of analysis.
• Secondary standard : A compound whose purity has been
established by chemical analysis and that serves as the
reference material for a titrimetric method of analysis
• Standardization : A process in which the concentration of a
solution is determined by using the solution to titrate a
known amount of another reagent.
Cont.

10. Requirement for Successful
Volumetric Titration
• Reaction must be stoichiometric, well defined
reaction between titrant and analyte.
• Reaction should be rapid.
• Reaction should have no side reaction, no
interference from other foreign substances.
• Must have some indication of end of reaction, such
as color change, sudden increase in pH, zero
conductivity, etc.
• Known relationship between endpoint and
equivalence point.

11. Properties of The Primary
Standard
• Be commercially available in a high state of purity
• Stable over long periods of time
• Not decompose when dissolved in water
• Not be volatile (so losses due to evaporation do not
occur)
• Not absorb water or carbon dioxide from the
atmosphere
• Reasonably large formula weight

12. Titration Curves
• Titration of acid/base reactions involve the process of
neutralization in order to determine an unknown
concentration.
• Acid-Base titrations can be made up of both strong
and weak acids or bases.
• However, in order to determine the unknown
concentration of an acid or base, you must add the
opposite so that neutralization can be reached.
• Therefore, an acid of unknown concentration will be
titrated using a basic standard solution and a base of
unknown concentration will be titrated using an acidic
standard solution.

13. • Acid-Base titrations often require the use of some kind of
indicator depending on the strength of acid or base that is
being titrated.
• In some cases a weak base or weak acid is used or a pH
meter which reads the pH of the solution being titrated.
• Once the pH of the titrated solution equals seven, either
indicated by a change in colour or on a pH meter one can
determine that titrations is complete.
Cont.

14. What happens during titration

15. • Examples of acid-base titrations include :
 Titration of a Strong Acid with a Strong Base
 Titration of a Weak Acid with a Strong Base
 Titration of a Weak Base with a Strong Acid
 Titration of a Weak Polyprotic Acid
Cont.

16. Cont.

17. • The standard solution is a strong acid and the
unknown concentration solution is a strong base.
• This can be acknowledged by the change in pH as
the standard solution is being added.
Strong Acid/Strong Base Curve

18. Cont.
• Since the graph begins at a high pH of 14 then the
original solution must be a strong base.
• The graph ends at pH close to 0 and it can be inferred
that the standard solution being added to reach
neutralization must be a strong acid.

19. Back Titration (Indirect Titration)
• Generally a two-stage analytical technique: Reactant A of
unknown concentration is reacted with excess reactant B
of known concentration.
• A titration is then performed to determine the amount of
reactant B in excess.
• Back titrations are used when:
 One of the reactants is volatile, for example ammonia.
 An acid or a base is an insoluble salt, for example
calcium carbonate
 A particular reaction is too slow

20. Example
A student was asked to determine the concentration of ammonia, a volatile substance, in a
commercially available cloudy ammonia solution used for cleaning.
First the student pipetted 25.00 mL of the cloudy ammonia solution into a 250.0mL conical flask.
50.00 mL of 0.100 mol L-1 HCl(aq) was immediately added to the conical flask which reacted with
the ammonia in solution.
The excess (unreacted) HCl was then titrated with 0.050 mol L-1 Na2CO3(aq). 21.50 mL of
Na2CO3(aq) was required. Calculate the concentration of the ammonia in the cloudy ammonia
solution.

21. Cont.
Step 1: Determine the amount of HCl in excess from
the titration results
2HCl(aq)+ Na2CO3(aq)→ 2NaCl(aq) + CO2(g)+ H2O(l)
Calculate the moles, n, of Na2CO3(aq) that reacted in
the titration
The amount of HCl that was added to the cloudy
ammonia solution in excess was 2.150 x 10-3 mol

22. Cont.
Step 2: Determine the amount of ammonia in the
cloudy ammonia solution
Calculate the total moles of HCl originally added
to the diluted cloudy ammonia solution:
n(HCltotal added) = 0.100 x 50.00 x 10-3 = 5.00 x 10-3 mol
Calculate the moles of HCl that reacted with the
ammonia in the diluted cloudy ammonia solution
n(HCltitrated) + n(HClreacted with ammonia) = n(HCltotal added)
n(HCltotal added) = 5.00 x 10-3 mol
n(HCltitrated) = 2.150 x 10-3 mol
n(HClreacted with ammonia = 5.00 x 10-3 mol - 2.150 x 10-3 mol = 2.85 x 10-3 mol

23. Write the balanced chemical equation for the reaction
between ammonia in the cloudy ammonia solution and
the HCl(aq).
NH3(aq) + HCl(aq) → NH4Cl(aq)
c = concentration (molarity) = 2.85 x 10-3 ÷ 25.00 x 10-3
= 0.114 mol L-1

24. • Consider the titration of 50.0 mL of 0.100 M HCl
using a titrant of 0.200 M NaOH.
• When a strong base and a strong acid react the
only reaction of importance is
• The first task in constructing the titration curve is to
calculate the volume of NaOH needed to reach the
equivalence point, Veq.
• At the equivalence point, moles HCl = moles NaOH
Constructing the
titration curve

25. Cont.
• The volume of NaOH needed to reach the
equivalence point is
• Before the equivalence point, HCl is present in
excess and the pH is determined by the
concentration of unreacted HCl.

26. • At the start of the titration the solution is 0.100 M in
HCl, which, because HCl is a strong acid, means that
the pH is
Cont.
• After adding 10.0 mL of NaOH the concentration of
excess HCl is
Step 2:

27. Cont.
Step 3: The pH at the equivalence point for the titration of a strong acid with a
strong base is 7.00.

28. Step 4: Calculate pH values after the equivalence point by determining the
concentration of excess titrant.
To find the concentration of H3O+ we use the Kw expression

30. GROUP ASSIGNMENT
Construct a titration curve for the titration of
50.0 mL of 0.0500 M HCOOH with 0.100 M NaOH
Show all calculations, tables and curve
To be submitted 9th March 2020 in class

31. Complexation reactions and titrations
Ligand: Is an ion or a molecule that forms a covalent bond
(involves sharing of electron pairs between atoms) with a
cation or a neutral atom by donating a pair of electrons, which
are then shared.
Water, ammonia and halide ions are common inorganic
ligands.
Example: we refer to Cu(II) dissolved in water as Cu2+, but it is
actually complexed by water to form species such as
Cu(H2O)4
2+
Formation of complexes

32. Formation of complexes
Coordination number: Coordination number of a cation is the
number of covalent bonds that it tends to form with an
electron donor (ligand). Typical values of the coordination
number is 2, 4 and 6. The specie that forms can be positive,
neutral or negative.
Example: Cu(II) has a coordination number of 4. It can form
cationic Cu(NH3)4
2+, neutral Cu(NH2CH2COO)2 and anionic
CuCl4
2- species

33. Formation of complexes
Chelate: Is produced when a metal ion coordinates with two or
more donor groups of a single ligand to form a five- or six-
member heterocyclic ring.
Example: Cu(II) and glycine
This is an example of a bidentate (mono/uni-, tri-, tetra-,
penta-, etc. dentate also occurs)

34. Titrations with inorganic complexing agents
Most simple inorganic ligands are mono/unidentate (only one
atom in the ligand binds to the metal), which can lead to low
complex stability and indistinct end points during titration. As
titrants multidentate ligands, particularly those having four or six
donor groups, have two advantages over their unidentate
counterparts:
• Generally react more complete with cations and thus produce
sharper end points
• Usually react with metal ions in a single step process, whereas
complex formation with unidentate ligands usually involves
two or more intermediate species.

35. Aminocarboxylic acid titrations
EthyleneDiamineTetraacitic Acid is the most widely used complexometric titrant.
Structural formula:
EDTA has six potential sites for bonding a metal ion: the four carboxyl groups and
the two amino groups. Thus, EDTA is a hexavalent ligand.
17D-1 EDTA

36. EDTA
Acid properties of EDTA: Dissociation of EDTA leads to the
formation of five species: H4Y, H3Y-, H2Y2-, HY3- and Y4-.

37. EDTA
Zwitterion: Is an ion that bears
both positive and negative
charge.

38. Complexes of EDTA and metal ions
EDTA is valuable as titrant, because:
• It combines with the metal ions in a ratio of 1:1 regardless of
the charge on the cation. Example
Ag+ + Y4- ↔ AgY3-
Al3+ + Y4- ↔ AlY-
• It forms chelates with all cations, except alkali metals
• Chelates are sufficiently stable for titrations

39. Titration methods employing EDTA – self study!
Example
17D-7
Titration methods
involving EDTA
Direct titration
(with 4 sub
headers)
Back titration
Displacement
methods

40. Titration methods employing EDTA
E.g. Back titration:
How: A measured excess of standard EDTA solution is added to the
analyte solution. After the reaction is complete, the excess EDTA is back-
titrated with cations for which a satisfactory indicator exists.
Why: i) Useful for the determination of cations that form stable
complexes with EDTA and for which a satisfactory indicator is not
available.
ii) It is also useful for cations that react slowly with EDTA.

41. Scope of EDTA titrations – self study!
Interference from a particular cation can sometimes
be eliminated by adding a suitable masking agent.
Masking agent: Is a complexing agent that reacts
selectively with a component in a solution to prevent
that component from interfering in a determination.

42. EDTA – something interesting
Chelation therapy is the use of chelating
agents, such as EDTA, to detoxify poisonous
metals such as mercury, arsenic and lead by
converting them to a chemically inert forms
that can be excreted without further
interaction with the body.

43. Determination of water hardness
What is hard water?
Is hard water a problem?
Practical examples of water hardness?

44. Example 1 of water hardness
Hard water contains calcium, magnesium and heavy metal ions that form
precipitates on taps and kettles.

45. Example 2 of water hardness
Water hardness is NB for industrial applications (e.g. cooling towers, pipes, etc.).

46. Example 3 of water hardness
Hard water contains calcium, magnesium and heavy metal ions
that form precipitates with soap. e.g. Mafikeng hard water that
forms scum in the bath.

47. How is water hardness expressed?
Hard water contains calcium, magnesium
and heavy metal ions that form
precipitates. [Ca] and [Mg] are usually
higher than other metal ions and the
hardness of water is therefore expressed as
equivalent of [CaCO3].

48. Determination of water hardness
Method:
i) Buffer sample to pH 10,
ii) followed by EDTA titration
iii) Mg forms least stable EDTA complex of all multivalent
cations and is therefore not titrated until other cations have
been complexed
iv) Therefore a Mg ion indicator is used (e.g. Calmagite,
Eriochrome Black T)
v) Often a small amount of Mg-EDTA chelate is added to ensure
satisfactory indicator action
Why Mg-EDTA in point v) and not un-complexed Mg?

49. Take home message
Know and apply:
• EDTA structure + dissociation
• Zwitterion definition + EDTA application
• Value of EDTA as a titrant
• Titration methods employing EDTA
• Masking / De-masking
• Chelation therapy
• Water hardness definition, implications thereof,
method for determination of water hardness