Q.1 What is the condition must require during titration?
Q.2 What is the different type of reaction usually occurs during titration?
Q.3 What is the requirements of primary standard?
Q.4 What are the substances commonly used as primary standard?
A secondary standard is a substance which may be used for standardizations, and whose content of the active substance has been found by comparison against a primary standard.
It follows that; a secondary standard solution is a solution in which the concentration of dissolved solute has not been determined from the weight of the compound dissolved but by reaction of a volume of the solution against a measured volume of a primary standard solution.
1. Acid-Base reactions:
ü Na2CO3,
ü Na2B4O7(Sodium tetrabromate),
ü KH(C8H404) (Potassium hydrogen phthalate),
ü KH(I03)2 (Potassium hydrogen iodate),
ü HCl,
ü C6H5COOH(Benzoic acid).
2. Complex formation reactions:
ü Ag,
ü AgNO3,
ü NaCl,
ü Various metals (pure Zn, Mg, Cu, Mn) and their salts.
3.Precipitation reactions:
ü Ag,
ü AgNO3,
ü NaCl,
ü KCl,
ü KBr.
4.Oxidation-reduction reactions:
ü K2Cr2O7,
ü KbrO3 (Potassium borate),
ü KIO3,
ü KH(I03)2 (Potassium hydrogen iodate),
ü Sodium Oxalate (Na2C2O4),
ü Arsenic (׀׀׀) oxide(As2O3)
A primary standard should satisfy the following requirements:
1. Purity:
It should be available in highly pure form. It should also preserve in a pure state.
2. Stability:
It should be stable (at 110˚c- 120˚c). There is no chemical change occurred.
3. Unaltered:
The substance should be unaltered in air during weighing, this condition implies that it should be hygroscopic, oxidized by air, or affected by CO2.The standard should maintain an unchanged composition during storage.
4. Test procedure:
The substance should be capable of being tested for impurities by qualitative and other tests of known sensitivity. (The total amount of impurities should not exceed 0.01%-0.02%)
5. Molecular weight:
It should have a high molecular weight so that the weighing errors may be negligible.
6. Solubility:
It must be readily soluble in the solvent.
7. Titration error:
The reaction with the standard solution should be stoichiometric and practically instantaneous. The titration error should be negligible, or easy to determine accurately by experiment.
A primary standard is a compound of sufficient purity from which a standard solution can be prepared by direct weighing of a quantity of it, followed by dilution to give a defined volume of solution.
Normality of a solution is defined as the number of equivalents of solute per litre of solution. It is denoted by ‘N’.
In titrimetry certain chemicals are used frequently in defined concentration as reference solution. Such substances are referred as primary standards or Secondary standards.
Molality of a solution is defined as the number of moles of solute per 1000gm of solvent. It is denoted by ‘m’.
No. Of mole of solute
Molality (m) =
