Midterm Flashcards
It is conducted by introducing a standard base solution gradually from a burette into a solution of the acid being assayed until chemically equivalent amounts of each have reacted.
Direct titration
It is used whenever the end point of a direct titration deviates from stoichiometric points for some reasons.
Residual/Back titration
It is used when the basic sample is insoluble in water and the rate of its reaction with the standard acid is virtually slow.
Residual/Back titration
In such procedure, the basic sample is treated with an amount of standard acid known to be in excess of a chemically equivalent amount, and the excess acid is subsequently titrated with a standard base.
Residual/Back titration
The amount of the standard acid which is chemically equivalent to the basic sample can be calculated by simply __________.
total amount of standard acid employed - amount of acid
The entire process is repeated in the absence of the analyte for correction purposes.
Blank determination
In such cases the actual volume of titrant equivalent to the substance being assayed is the __________.
difference between the volume consumed in the residual blank titration and that consumed in the titration with the substance present.
The corrected volume so obtained is used to calculate the __________.
quantity of the substance being titrated
Titrant used in a direct acidimetric titration
acid (sulfuric acid or hydrochloric acid)
Analyte or primary standard used in a direct acidimetric titration
base (sodium carbonate)
Examples of direct acidimetric method
- Assay of sodium carbonate
2. Assay of sodium hydroxide
Analyte used in a residual acidimetric titration
base
Excess titrant used in a residual acidimetric titration
acid
Back titrant used in a residual acidimetric titration
base
Examples of residual acidimetric method
- zinc oxide
- milk of magnesia
- beef extract
- methenamine
