Tungsten trioxide (WO3) has a rich yellow color and is often used as a pigment i
ID: 855734 • Letter: T
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 10.22 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 14.66 mL of 0.08808 M potassium permanganate (KMnO4) to reach the purple endpoint. A blank required 0.26 mL. Balance the reaction below and determine the percent WO3 in the ceramic sample.
The Balanced reaction is : 3 MnO4 + 5 W + 4 H ------> 3 Mn + 5 WO2 + 2 H2O
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 10.22 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 14.66 mL of 0.08808 M potassium permanganate (KMnO4) to reach the purple endpoint. A blank required 0.26 mL. Balance the reaction below and determine the percent WO3 in the ceramic sample.
The Balanced reaction is : 3 MnO4 + 5 W + 4 H ------> 3 Mn + 5 WO2 + 2 H2O
sample taken=10.22g reduced to W3
solution prepared=500mL
sample taken=100mL=1/5 of original volume
3 MnO4 + 5 W + 4 H ------> 3 Mn + 5 WO2 + 2 H2O
volume of KMnO4sed for blank=0.26mL
Volume of KMnO4 used for sample=14.66-0.26=14.4mL
moles of KMnO4 used=0.08808moles/L*0.0144L=0.00127moles
from above equation 3mole of MnO4- reacts with =1.667 molesof W3
0.00127moles of KMnO4 reacts with=1.667/3*0.00127=0.00071 moles of W3
so 0.00071moles of W3 arepresent in(100mL) 1/5volume so
total of 0.00353moles of W3 present
Next Three moles of WO3 are produced from one moles of W3 hence
moles of WO3=3*moles of W3=3*0.00353moles=0.0106moles
mass of WO3=0.0106moles*231.84g/mole=2.454g
%age of WO3=2.454g/10.22g*100=24.01%
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