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Primary standards – Criteria, Properties and Examples

What is a Primary Standard?

Primary standard is a compound of  sufficient purity from which standard solutions of known normalities can be prepared by direct weighing of it and diluting to a defined volume of solution.

Examples

Sodium carbonate Na2CO3
Sodium borate Na2B4O7
Potassium hydrogen iodate KH(IO3)2
Pure metals and their salts like Zn, Mg, Cu, Mn, Ag, AgNO3 , NaCl, KCl, KBr   – used in Acid base titrations
K2Cr2O7, KBrO3, KIO3, KI(IO3)2, NaC2O4, As2O3, pure iron – used in redox titrations

Eligibility criteria for a primary standard

A primary standard should satisfy the following conditions

primary standard

primary standard

  1. should be very pure
  2. should neither be deliquescent (absorbing moisture) nor efflorescent (losing water)
  3. should have high molecular weight so that weighing errors can be minimised
  4. should be chemically stable
  5. shall be readily soluble under given conditions
  6. it should react stoichiometrically

For more information one can read Benteley and Driver’s Textbook of Qualitative chemical analysis

 

 

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