Tungsten trioxide (WO3) has a rich yellow color and is often used as a pigment i

Question

Tungsten trioxide (WO3) has a rich yellow color and is often used as a pigment in ceramics and paints. In order to test a ceramic vase for its WO3 content, a 10.00 g sample of the vase was ground and reduced with Pb(Hg) to convert any WO3 to W3 . The resulting W3 was transferred to 500.0 mL of 1.00 M HCl. A 100.00 mL aliquot of the HCl solution required 12.64 mL of 0.08362 M potassium permanganate (KMnO4) to reach the purple endpoint. A blank required 0.13 mL. Balance the reaction below and determine the percent WO3 in the ceramic sample.

Explanation / Answer

Balancing the reaction -

MnO4^-1(aq) + 4H2O(aq) = Mn^2+(aq) + 8H^+(aq) + 11e-

W^3+(aq) + 2H2O(aq) = WO2^2+(aq) + 4H^+(aq) + 3e-

Net equation -

MnO4^-1(aq) + W^3+(aq) + 2H2O(aq) = Mn^2+(aq) + WO2^2+(aq) + 4H^+(aq) + 8e-

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