Answer to Question #37563 in Chemistry for shahin

Question

Hello. Using a formula to determine the unknown concentration of the redox titration, how?

Answer 1

In the equivalence point number of equivalents of analyte (substance of unknown concentration) is equal to number of equivalents of titrant:
Eq_a = Eq_t
Number of equivalents is equal to product of volume and normality. So, in the equivalence point:
N_a•V_a = N_t•V_t
Normality of titrant is known, volume of titrant consumed to reach the equivalence point is also known (determined by titration) and volume of analyte taken for titration is also known. So, normality of analyte:
N_a = (N_t•V_t)/V_a
Molar concentration (molarity) Ca of a solution may be calculated based on the solution normality. The normality of the solution is defined as the molar concentration divided by an equivalence factorf_eq. So, molar concentration of the analyte:
C_a = N_a•f_(eq a) = (f_(eq a)•N_t•V_t)/V_a
If the titrant solution concentration is given as molarity, not as normality, the formula to determine unknown concentration:
C_a = (f_(eq a)•C_t•V_t)/f_(eq t)•V_a
In redox titration, the equivalence factor is equal to the number of electrons that an oxidizing or reducing agent accepts or donate in redox reaction occurring during the titration.
So, to be able to determine the unknown concentration one should write down the redox reaction (better as two half-reactions) and determine how many electrons are accepted by oxidant and donated by reducer.