CLASSICAL METHODS

TITRIMETRY / VOLUMETRIC ANALYSIS

Involves a solution of reagent of known concentration (titrant) added to a solution of analyte until a reaction is judged complete (endpoint)

Biuret

• For accurate transferring of the titrant

• ‘blank’ with glass stopcock is used for acids

Erlenmeyer Flask

for swirling the contents

Wash Bottle

• For washing the drops of titrant clinging to the tip of the biuret

• Contains the solvent

Volumetric Flask

used for quantitative preparation of titrant

Titrant / Std Solt’n / VS

reagent of known concentration

Titrand / Analyte / Sample

active constituent being analyzed; unknown concentration

Indicators

compounds capable of changing colors which aid in the visualization of the endpoint

Endpoint

• Point at which the reaction is observed to be complete (color change)

• Only an estimation of the equivalence point

Equivalence / Theoretical / Stoichiometric Point

• Point at which a chemically equivalent amount of titrant has reacted with the analytes

• Ex. Potentiometry, Electrometry

Titration Error

𝑬𝑻 = 𝑽𝒆𝒑 − 𝑽𝒆q

Blank Titration

• Entire procedure is repeated except that the analytes is omitted

• For correction and to enhance the reliability

STANDARDIZATION

Process of determining the exact concentration if the titrant

• Primary Standard

• Secondary Standard

• Standardization Computation

Primary Standard

• Substance of high degree of purity (ultrapure; 100%)

• Reference material in titrations

• Used in direct standardization

• Examples:

o KHP (Potassium-H-phthalate) – NaOH VS, KOH VS

o K2Cr2O7 – Na2S2O3 VS

Secondary Standard

• Standard solution whose purity has been determined by chemical analysis

• Used in indirect standardization

• Examples:

o Na2S2O3 VS – I2 VS

o Na2 EDTA TS – ZnSO4 VS

Normality (N)

number of gram equivalent weight of a solute in 1L solution

Normality Factor (f)

based on the type of reaction induced; factor of the std

ACID

f = no. of replaceable H+

• HCl ↔ H+ + Cl- (f = 1)

• H2SO4 ↔ 2H+ + SO4 2- (f = 2)

• CH3COOH ↔ H+ + CH3COO (f = 1)

• H3BO3 ↔ H+ + H2BO3 - (f = 1)

• H3PO4 ↔ 2H+ + HPO4 - (f = 2)

BASE

f = no. of replaceable OH-

• Ca(OH)2 ↔ Ca2+ + 2OH- (f = 2)

• MgO + H2O ↔ Mg2+ + 2OH- (f = 2)

SALTS

f = no. of (+) or (-) charges

• Na2CO3 ↔ 2Na+ + CO3 2- (f = 2)

Redox

OA: f = no. of e- gained, e.g. I2 → 2I- (f = 2)

RA: f = no. of e- lost; e.g. Fe2+ → Fe3+ (f = 1)

Precipitation

HALIDE SALT: f = no. of (+) or (-)

• BaCl2 ↔ Ba2+ + 2Cl- (f = 2)