Dichromate ion, Cr_2O_7^2, oxidizes methanol, CH_3OH, to formaldehyde, CH_2O, un

Question

Dichromate ion, Cr_2O_7^2, oxidizes methanol, CH_3OH, to formaldehyde, CH_2O, under acidic conditions. cr_2O_7^2-(aq)+H^+(aq) + e^- rightarrow Cr^3+(aq) + H_2O(l) E degree = +1.36 CH_2O(aq) + H^+ (aq) + e^- rightarrow CH_3OH(aq) E degree = -0.237 V Fe^3+ (aq) + e^-e rightarrow Fe^2+(aq) 60.00 ml. of 0.2007 M Cr_2O^2-_7 was added to^^10.00 mL of a solution containing methanol in water. The excess Cr_O_7^2- was then titrated with 39.84 mL of 0.2500 M Fe^2+ solution. Determine the molar concentration of methanol in the CH_3OH/H_2O solution.

Explanation / Answer

number of moles of Cr2O7-  = 0.06 L x 0.2007 M = 0.012042 moles

number of moles of Fe2+ = 0.03984 L x 0.2500 M = 0.00996 moles

the excess Cr2O7- titrated with Fe2+

0.00996 moles of Cr2O7- consume with Fe2+ remaining Cr2O7- titrated with methanol solution

0.002082 moles titrated with methanol solution

concentration of methanol = 0.002082 moles / 0.01 L = 0.2082 M

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