Quant ch.7

reagent grade chemicals

meet purity requirements by ACS

trace metal grade chemicals

reagents have extremely low impurities, important for trace analysis

volumetric analysis

procedures that measure volume of reagents needed to react with analyte

titration

increments of reagent solution added until the reaction b/w analyte and titrant is complete

titrant

reagent solution, usually delivered from buret

analyte

quantity calculated from amount of titrant consumed in reaction

requirements for titrations

• reaction must have large equilibrium constant

• reaction must proceed rapidly

• each increment of titrant should be completely and quickly consumed

• analyte should be completely used up

equivalence point

quantity of added titrant is exact amount necessary for stoichiometric reaction with the analyte (ideal theoretical result based on stoichiometry)

end point

actual measurement, marked by sudden change in physical property of the solution.

• End point does not = equivalence point because extra titrant, beyond what is needed to react is required to see the purple color

indicator

compound with physical property (usually color) that changes abruptly near the equivalence point.

titration error

difference between end point and equivalence point

blank titration

carry out same titration procedure on similar solution without the analyte

• provides estimate of titration error

• subtract blank titration volume from volume observed in analytical titration

primary standard

• pure and stable enough to be used directly after weighing.

• 99.99% pure

• should not decompose during storage

• stable when dried by heat or vacuum

• stoichiometry of reaction with titrant must be known

standardization

• prep a titrant with approx the desired concentration and use it to titrate a primary standard

• method can be used to determine conc. of the titrant

• validity of analytical result ultimately depends on knowing the conc. of the primary standard

direct titration

add titrant to analyte until reaction is complete

back titration

1. add known excess of one standard reagent to analyte

2. titrate excess with second standard reagent

when is back titration useful?

• when endpoint of back titration is clearer than direct titration

• when an excess of the first reagent is required for complete reaction with analyte

gravimetric titration

measures the mass of titrant solution delivered in each increment

titration curves

shows how conc. of reactant varies as titrant is added

what is sharpness of endpoint influenced by?

• concentration of analyte and titrant

• size of solubility product (Ksp)