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 10.19 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 10.13 mL of 0.08840 M potassium permanganate (KMnO4) to reach the purple endpoint. A blank required 0.18 mL. Determine the percent WO3 in the ceramic sample.
I'm sorry but I don't know what to do with the W3 in HCl. Does it form WCl3? and is it oxidized with permanganate to W^6+
To determine the percent WO3 in the ceramic sample, we need to follow a series of steps to calculate the amount of WO3 and then express it as a percentage of the sample.
1. First, let's calculate the moles of KMnO4 used in the titration:
The volume of KMnO4 used is 10.13 mL (subtracting the blank volume of 0.18 mL).
Molarity of KMnO4 = 0.08840 M.
Thus, moles of KMnO4 = volume (in L) × molarity = 10.13 mL × (1 L / 1000 mL) × 0.08840 M.
2. Now, we need to calculate the amount of WO3 present in the aliquot of the HCl solution.
Using the balanced equation:
5HCl + 2KMnO4 + 3H2O → K2MnO4 + 5Cl^- + 2MnO2 + 8H+
From the stoichiometry of the equation, we know that 2 moles of KMnO4 react with 5 moles of HCl. Therefore, moles of HCl in the aliquot = (moles of KMnO4) × (5 mol HCl / 2 mol KMnO4).
3. Next, we can calculate the number of moles of HCl in the 100.00 mL aliquot.
Molarity of HCl = 1.00 M.
Volume of HCl solution used = 100.00 mL (0.10000 L).
Thus, moles of HCl in the aliquot = volume (in L) × molarity = 0.10000 L × 1.00 M.
4. Now, we can calculate the number of moles of HCl used in the reaction with WO3:
moles of HCl used in the reaction with WO3 = moles of HCl in the aliquot - moles of HCl in blank.
5. Next, we need to determine the number of moles of WO3 that reacted with the HCl in the reaction:
According to the balanced equation, 5 moles of HCl react with 1 mole of WO3. Therefore, moles of WO3 = (moles of HCl used in the reaction with WO3) / 5.
6. Finally, we can calculate the percent WO3 in the ceramic sample:
mass of sample = 10.19 g.
moles of WO3 = moles of WO3 × (molar mass of WO3 / molar mass of WO3).
The molar mass of WO3 is 231.84 g/mol.
Finally, percent WO3 in the ceramic sample = (moles of WO3 / mass of sample) × 100%.
Performing these calculations should give you the desired result: the percent WO3 in the ceramic sample.