Principles of Titration and Errors ( Dr. A. Amsavel )

Principles of Titration and errors

By Dr. A. Amsavel

Introduction

Volumetric analysis
 Simple and easy
 Fast and can be done on site
 Less expensive
 Estimation of content or Assay
 Precise and accurate
 Depends on method and specificity

Requirements of a Titration Reaction

Reaction must complete by 99.9 % so that < 0.1 % (or 1 ppt) remains unreacted
Rxn must be rapid
Titration needs to be performed in a reasonable time period
The stoichiometry must be well defined, and known
It can be predicted from equilibrium constants
A method must be available to determine the equivalence point

Types of Titration

1) Precipitation
– A(aq) + B(aq) = AB(s)
2) Acid-Base rxn
– H+ + OH ̄ = H2O (strong acids or bases)
– HA + OH ̄ = H2O + A ̄ (weak acids)
– A ̄ + H+ = H2O + HA (weak bases)
3) Complexation rxn
– Zn2+ + 4NH3 = Zn(NH3)42+
4) Redox rxn (oxidation-reduction)
– Fe2+ + Ce4+ = Fe3+ + Ce3+

Standards

• Measurements are made with reference to standards
– The accuracy of a result is only as good as the quality and accuracy of the standards used
– A standard is a reference material whose purity and composition are well known and well defined
• Primary Standards
– Used as titrants or used to standardize titrants
– Requirements
• Usually solid to make it easier to weigh
• Easy to obtain, purify and store, and easy to dry
• Inert in the atmosphere
• High formula weight so that it can be weighed with high precision

Endpoint Detection

It is critical, to know the completion of reaction / determination
1) Visual indicators:
• Observe a colour change or precipitation at the endpoint.
– Rxn progress checked by addition of external or self indicator
2) Photometry:
• Use an instrument to follow the colour change or precipitation
3) Electrochemistry:
• Potentiometry – measure voltage change ( pH electrode)
• Amperometry – measure change in current between electrodes in solution
• Conductance – measure conductivity changes of solution
Later two used for coloured, turbid, end point accurate

Acid-base titration

 Neutralization titration
 Neutralization Indicators
 Indicators & mixed indicators
 Neutralization curve
 Non-aqueous titration


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