In: Chemistry
A 49.96 mL sample containing La3+ was treated with
sodium oxalate to precipitate
La2(C2O4)3, which was
washed, dissolved in acid, and titrated with 18.04 mL of 0.006363
MKMnO4. Calculate the molarity of
La3+ in the unknown.
(Hint: the reaction involved in the titration was: permanganate
ion(s) + oxalate (ions) -----> manganese(II) ions + carbon
dioxide. The reaction occurred in acidic aqueous solution)
Reaction,
2MnO4- + 5C2O4^2- + 16H+ ---> 2Mn2+ + 10CO2 + 8H2O
moles of KMnO4 used = 0.006363 M x 18.04 ml
= 0.1148 mmol
moles of C2O4^2- reacted = 0.1148 x 5/2
= 0.287 mmol
moles of La3+ present = 0.287 x 2/3
= 0.1913 mmol
molarity of La3+ in the unknown = 0.1913/49.96
= 0.00383 M