1-Introduction.pdf

Pharmaceutical Analytical Chemistry - 1
Dr. Inas A. Abdallah
E- mail: Inas.Abdallah@fop.usc.edu.eg

Determination Vs Quantitative Analysis

Quantitative Analysis
It is classified into:
1- Volumetric Analysis:
• A measurement by volume of a solution is made to determine the % (v/v or
w/v) of a substance.
• Among the most useful and accurate analytical techniques, especially for
millimole amounts of analyte.
• They are rapid and can be automated.

Quantitative Analysis
2- Gravimetric Analysis:
• Determination by weight of a final product with known and definite chemical
structure.
3- Instrumental analysis:
• Determination by measuring some physical properties by using an
instrument which include colorimetry, potentiometry.

What is meant by Titration?
Titration:
• measurement of the capacity of substance
to combine with a known standard reagent
in a quantitative way.

Titration:
• The aim of any titration is the addition of
a standard solution in such amount as to be
chemically equivalent to the substance
with which it reacts.
• This condition is achieved at a point
which is known as the Equivalence point.
The exact volume of the standard solution
is used to calculate the quantity of the
material to be analyzed.

Equivalence point:
• A theoretical concept. Its real position can
only be theoretically calculated;
• Practically this point is known as Endpoint
• Special chemical substances are used to
observe these changes known as Indicators
End point – Equivalence point = titration error

Reactions in Volumetric Analysis
• Any titration is based on a specific chemical reaction.
• The requirements for the ideal chemical reaction for titration:
1- Complete reaction.
2- Must be represented in a balanced chemical equation; free of any side reactions.
3- Available and accurate method for detecting the endpoint.

Types of Reactions in Volumetric Analysis
Volumetric methods are divided into 4 categories:
1- Neutralization reactions (acid base reactions):
H+ + OH- ⇋ H2O
2- Precipitation reactions:
Ag+ + Cl- ⇋ AgCl ↓
3- Complex formation reactions:
Hg2+ + 2Cl- ⇋ HgCl2
4- Redox reactions (oxidation –reduction reactions)
Ce4+ + Fe2+ ⇋ Ce3+ + Fe3+

Detection of Endpoint
1- Some titrants can be used as self-indicators e.g.: KMnO4.
2- The formation or disappearance of an insoluble phase (turbidity).
3- Change of refractive index of the solution.
4- Measuring the change in electrical potential of the solution.
5- Measuring the change in electrical conductivity or current of the solution
6- Change of temperature of the solution.

Titration methods
1- Direct titration:
• Stepwise addition of the titrant (standard solution) to the substance until
completion of the reaction as shown by the color change of the indicator.

Titration methods
2- Back titration :
• A measured excess of the standard solution is added to the sample. Then after
the completion of the reaction the remaining unreacted excess of the standard is
titrated against another standard solution.
• This method is used when the chemical reaction is slow, or when the suitable
indicator is not available.

Titration methods
3- Substitution reaction:
• The titration of weak acids (or bases) with standard strong acids (or bases).
• Titration of borax and sodium carbonate with strong acid.
HCl + Na2B4O7 + 6H2O → 4H3BO3 + 2NaCl + H2O
2 HCl + Na2CO3 → H2CO3 + 2NaCl

Primary standard solutions and substances
1- Primary standard solution:
• A solution whose concentration should remain constant for a long period.
• It is prepared by direct weighting of a primary standard substance in a measuring flask,
dissolving and completing to volume.
2- Secondary standard solution:
• The concentration of which can be directly calculated from the weight of the solute and volume of
the solution.
• The concentration can only be known approximately.
• The exact concentration is determined by:
1- Titration against a primary standard solution.
2- Titration against another well-known standardized secondary standard.

Requirements of primary standard substance
1- Must be easily obtained in very high grade of purity and of known
composition.
2- Very stable, and resists reactions with air.
3- Stable against heat at 105-110°C.
4- It should have high equivalent weight to minimize weighing error.
5- It must react with other substances in a quantitative way according
to a balanced chemical equation.

Examples of primary standard substances
1- Acids: Potassium acid phthalate, oxalic acid, benzoic acid.
2- Bases: Borax, sodium carbonate.
3- Oxidizing agents: Potassium dichromate, potassium bromate
4- Reducing agents: sodium oxalate, and potassium ferrocyanide.

Methods of expressing concentration of standard solutions
1- Molar solution:
• it is a solution of the substance containing one gram molecular weight of the substance
per one liter of solution.
• Molarity (M): is the No of gram molecular weight of solute per one liter of solution.

Methods of expressing concentration of standard solutions
2- Normal solution:
• Contains one gram equivalent weight of solute per liter of solution.
• Normality (N): is the No of gram equivalent weight per liter of solution.
• The advantages of expressing concentrations in terms of equivalent is:
the 1:1 ratio of all reactions of this type.
1eq. HCl= 1 eq. H2SO4 = 1 eq. NaOH

Equivalent weights and milliequivalent weights
• They are the most commonly used unites in volumetric analysis.
• The equivalent weight may assume 2 or more values for the same
compound if the reactions are different.
• Thus the definition of the equivalent weight for a chemical compound
always refers to a specific chemical reaction.

1- In neutralization reactions:
• The equivalent weight is that weight of the substance which either contributes or reacts
with one gram formula weight of hydrogen ions in that reaction.
• Acids and bases with single H+ or OH- ion their equivalent eight = Molecular weight.
• In cases that the acid has two reacting H+ and when these two hydrogen involved in the
reaction the equivalent weight =1/2 Molecular weight.
• H2CO3 → CO2 + H2O 𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 =
𝑴𝒐𝒍𝒆𝒄𝒖𝒍𝒂𝒓 𝒘𝒆𝒊𝒈𝒉𝒕
𝟐

• In case of only one hydrogen is involved in the reaction e.g. phosphoric acid.
• H3PO4 + OH- → H2 PO4 + H2O 𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 =
𝟏
• H3PO4 + 2OH- → HPO4 + 2H2O 𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 =
𝟐
2- Redox reactions : ( Oxidation – reduction):
• Is that weight that donates or accepts one electron.
𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝑾𝒆𝒊𝒈𝒉𝒕 =
𝑪𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒐𝒙𝒊𝒅𝒂𝒕𝒊𝒐𝒏 𝒏𝒖𝒎𝒃𝒆𝒓

3- In precipitation and complex formation reactions:
• Is the weight of the substance which consumes or reacts with 1 g equivalent weight of
the reacting cation, if it is univalent e.g. Ag .
• or Molecular weight/2 if it is divalent.

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