Titrations Flashcards
What is a titration
Lab method used for quan analysis
Why titration
Determine unidentified concentrations of known analyte
Volumetric analysis
Volume measurement
Titrant
Slow addition of one solution of known concentration
Why in pharmacy
Content analysis of active ingredients/ drugs and raw materials can be performed easily quickly reproducible and accurate
Pharmaceutical applications
Pharm compounds are weak acids/bases that can be analysed by aqueous/ non aqueous titration
Eg salicylic acid/ caffeine
Amino acids
Assay of drugs- weak chromophore
Karl fischer titration
Find water content
Based on oxidation reaction of iodine and sulphur
Endpoint when all water used up
Volumetric titration
Suitable to determine water content down to 1 %
End point potentiometrically
Coulometric determination
Endpoint detected electrochemically
How do pharm use titration
Determine unknown of chem in blood and urine
Development of new pharmaceutical
Determine fat content water and vitamins
Titrant
Reagent of known standard concentration added ro solution containing analyte
We measure its volume
(In the burrette)
Analyte
Solution of unknown
In beaker
Role of Indicator
Added to analyte solution to indicate end point by change in colour
Equivalence point
Mixture with stoichiometrically equivalent amount of titrant and analyte
End point
Point in titration when we stop adding titrant
Titration error
Error due to difference between end point and the equivalence
Acid base titration
Acidic or basic titrant reacts with an analyts thats is a base or an acid
Complexometric titration
Metal/ligand reaction
Redox titrations
Oxidising or reducing titrants reacts with an analyte
Precipitation titration
Titrant reacts with an analyte to form a precipitate
Back titration/ reverse titration
endpoint hard to identify
Excess volume another reactant with known conc
excess titrated
What is an Acid base titration used for
Used for analysis of organic compounds eg pharmaceuticals/ agricultural/ and environment labs
Kjedahl method
Primary standard
Pure and stable chemical compounds used to standardise the standard solution in titration
Standardisation of acidic and basic titrants
Standardising achieved by titrating known volume of titrants with other titrant of EXACT concentration
How does phenophthalein work
Weak acid which dissociates in water forming pink anions
How do Acid base indicators work
Weak acids bases
Dissolved in water dissociates slightly and form ions
Equilibrium in acid and alkaline conditions
Acid left
Alkaline right
Titration curve
Graph showing progress of titration as a function of volume of titrant added
Requirements for acid base titration
Substances react quickly and completely in precise stoichiometric quantities
Amount of solute in moles
Conc in mol/dm3
X
Volume dm3
Molarity (base) x volume (base)
Molarity (acid) x volume (acid)
Complexometric titration
Complexation reaction between analyte and titrant
What is a comp recation limited to
Metals that only form a single stable complex
Based on lewis/base reaction
Example of complexo reaction
EDTA forming a strong 1:1 complex with many metal ions
Use of complexo in pharma
Determine metal content of drugs
EDTA
Provides e- and has 6 binding sites
Forma stable metal ligand complex
1:1 stoichiometry
Limitation of EDTA
EDTA complex less stables as ph decreases and end point less distinct
Properties of Metal ion indicator
Compound changes colour when binding to a metal ion
MUST bund weaker than EDTA
+
Release metal ion to EDTA
Determination of endpoint in complexo titrations with EDTA
Metal ion indicator
Mercury electrode
Ph electrode
Ion selective electrode
What is redox reaction based on
Oxidaton/ reduction between analyts and titrant
Redox titration indicators
Diphenylamine
Monitor for redox
Electrochemical potential
Pharma analysis for redox
Determine conc of VLGH in pure medicines and tablets
Precipitation titration
Analyt + titrant form insoluble precipitate
Mohr method
Cl- using AG as titrant = reddish Ag2CrO = end point
What can precipitation in a reaction be used as
Visual indicator
Determine salt content in water
Back titration
no suitable sensor available / too slow for direct practical titration
Process of back titration
Volumetric analysis EXCESS reagent added
Unreacted reagent determined by titration = amount of substance in original test solution to be calculated
Pharm analysis of back titration
Determine amount if acetylsalicylic acid in aspirin
Positives of titrimetric analysis
Precise and accurate
Robust and reasonable priced equipment
Manual or automated analysis
Cheap
Limitations of titrimetric analysis
Non selective
Time consuming
Large amount of sample
Analyte must be reactive
