INTRODUCTION TO TITRATION

Titrimetry

_______ is a term which includes a group of analytical methods based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte.

Volumetric titrimetry

It is used to measure the volume of a solution of known concentration that is needed to react completely with the analyte.

Gravimetric titrimetry

It is like volumetric titrimetry, but the mass is measured instead of the volume.

Coulometric titrimetry

It is where the reagent is a constant direct electrical current of known magnitude that consumes the analyte; the time required to complete the electrochemical reaction is measured.

standard solution; analyte

Titration is a process by adding a _____ from a burette or other liquid-dispensing device to a solution of the ___ until the point at which the reaction is believed to be complete.

Standard solution

It is reagent of a known concentration which is used in the titrimetric analysis.

titrant

Standard solution is also known as the ____ in the titration process

Back titration

It is a process that is sometimes necessary in which an excess of the standard titrant is added, and the amount of the excess is determined by back titration with a second standard titrant.

Equivalence point

the point in which the amount of added titrant is chemically equivalent to the amount. of analyte in a sample.

End point

the point in titration when a physical change occurs that is associated with the condition of chemical equivalence.

Indicators

____ are used to give an observable physical change (end point) at or near the equivalence point by adding them to the analyte.

Titration error

It is the difference in the volume or mass of reagent between the equivalence point and end point.

Primary standard solution

It is a highly purified compound that serves as a reference material in all volumetric and mass titrimetric properties.

Secondary standard solution

It is a compound whose purity has been established by chemical analysis and that serves as the reference material for titrimetric method of analysis.

Ideal standard solution

1. Be sufficiently stable

2. React rapidly with the analyte

3. React completely wit the analyte

4. Undergo a selective reaction with the analyte

Direct method

a carefully weighed quantity of a primary standard is dissolved in a suitable solvent and diluted to a known volume in a volumetric flask.

Standardization

the titrant to be standardized is use to titrate (1) a weighed quantity of a primary standard, (2) a weighed quantity of a secondary standard, or (3) a measured volume of another standard solution

Molarity (c or M)

gives the number of moles of reagent contained in one liter of solution

Normality (Cn or N)

gives the number of equivalents of reagent in the same volume

For molarity

moles of analyte = moles of titrant which can be expressed as: M1V1 = M2 V2

For normality

no. of equivalents of analyte = no. of equivalents of titrant which can be expressed as: N1V1 = N2 V2

Titration curves

_____ consist of a plot of reagent volume on the horizontal axis and some function of the analyte or reagent concentration on the vertical axis

sigmoidal curve

important observations are confined to a small region (typically 60.1 to 60.5 mL) surrounding the equivalence point. It offers the advantages of speed and convenience.

linear segment curve

measurements are made on both sides of, but well away from, the equivalence point. Measurements near equivalence are avoided.