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 10.17 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 13.29 mL of 0.08146 M potassium permanganate (KMnO4) to reach the purple endpoint. A blank required 0.28 mL. Balance the reaction below and determine the percent WO3 in the ceramic sample.

Explanation / Answer

sample taken=10.17g reduced to W3

solution prepared=500mL

sample taken=100mL=1/5 of original volume

MnO4- +W3+=Mn2+ +WO2 2-

moles of KMnO4 used=0.08145moles/L*0.0131L=0.00106moles

from above equation 1mole of MnO4- reacts with one mole of W3

hence 0.00106moles of W3 are present in 1/5volume so total of 0.0053moles of W3

Next Three moles of WO3 are produced from one moles of W3 hence

moles of W=moles of WO3=0.016moles

mass of WO3=0.016moles*231.84g/mole=3.71g

%age of WO3=3.71/10.17*100=36.47%

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