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 10.30 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 13.25 mL of 0.09769 M potassium permanganate (KMnO4) to reach the purple endpoint. A blank required 0.09 mL. Balance the reaction below and determine the percent WO3 in the ceramic sample.

Explanation / Answer

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 10.30 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 13.25 mL of 0.09769 M potassium permanganate (KMnO4) to reach the purple endpoint. A blank required 0.09 mL. Balance the reaction below and determine the percent WO3 in the ceramic sample.

volume of KMnO4 used=13.25-0.09mL=13.16mL

Moles of KMnO4 used=0.01316L*0.09769moles/L=0.001287moles

moles of W3 present in 100mL=0.001287moles (assume they react 1:1, if they react 1:2 or 1:3 then moles of w3 ewould be0.001287*2 or 0.001287*3 respectively from balance chemical equation)

moles of W3 present in 500mL=above answer*5=0.001287moles*50=0.006435moles

(assume all WO3 has converted to W3)

moles of WO3 present=moles of W3*3=0.0193moles

mass of WO3=moles*mol mwt=0.0193moles*233.84g/mole=4.51g

mass of WO3 taken=10.30g

%age of WO3 in vase=4.51/10.3*100=43.82%

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