Question

4. (10 points) A student is given the assignment to determine the mass iron in a brand of women's vitamins. He begins by taking four vitamin tablets, grinding the tablets into a fine powder to undergo the necessary sample preparation to free all iron from the sample matrix and to reduce all iron to the +2 state. The resulting Fe2+ solution is transferred to a 250 mL volumetric flask and diluted to volume with distilled water. A 50 mL aliquot of the sample requires 42.98 mL of 1.00 x 10-'M Cr, in acidic pH. a) Write the two half-reactions. b) Balance the redox reaction. c) Calculate the mg Fe per tablet.

Answer 1

The geactien taking place between Cr0t and fe can be usictten au 2- Ondation (Fe Fet e Cr0 Reduction 2C3+ +6e Multhly e wnth 6 and ie, 6 x + to (2 addig Balaned Net eauation Cr201 6 Fe2+ 2c3t6Fet+ 7H0 + 144+ Groeqid Volume 42 48ml e .xlo M C0 42-98 ml x l0mol o.04248 mmol Clear Pram equation that . 0.04299 mmol e C0 would heact with Now 250 ml e elution lontairs 1 mmol e Cr,0 react with 6 mmel Ae24 2094 Mmol of fet 0.04298 x6 0.25780 mmol fe+ mass z mole x molar mas Thas much P prenent in 5o mL Sampe Moleady 1-284 NG mx 55.95 9 mel mars = 0.0 72013 of fe 0.25488Xo ma 50 xlo3 L moles 구2, 이즈 mg Volume 5.1576 지6md 니 SInce we fave used 4 fe-tablats man e 1-tablet 72.013-18 mg (Fein Thus, 25oml oseldio must tave same mdarchy i'e,5.1576 X53 M mdes Molarety XVolune = 5.1576xl0 mol x 250 mL Tun Che tto tablat cotais | 18 mg fe 18mg fe tablet 12094 mmal ofa teat