Question

what r primary and secondary standard substances?

Answer 1

a primary standard if a substance is known high purity which may be dissolved in a known volume of a solvent is given a primary standard solution if stoichiometry is used to establish the strength of a titrant is called the secondary standard solution

Answer 2

secondary standards :-
substance substance which cannot kept open place and they easily react with the components of air (O2 ,CO2 etc) react with balance when they are weighting are called secondary standard substance .
e.g. hcl ,H2So4,KOH ,NAOH are the secondary standard.
primary standard substance the substance which do not react with the components of air (O2 , CO2 etc)in open state and retained its composition for a long time is called primary standard substance.
e.g. NA2CO3 , Kr2Cr2O7....