A 2.80-g sample of haematite ore containing Fe3+ ions was dissolved in a concentrated acid and the solution was diluted to 250 mL. A 25.0 mL aliquot was reduced with Sn2+ to form a solution of Fe2+ ions. This solution of Fe2+ ions required26.4mL of a 0.0200 M K2Cr2O7 solution for complete oxidation back to Fe3+ ions. In the process Cr2O72- ions were converted to Cr3+.
masses, g/mol: Fe = 55.85 ; Fe2O3 = 159.7)
Calculate the percentage of Fe2O3 in the ore. (Molar
To calculate the percentage of Fe2O3 in the ore, we need to determine the amount of Fe2O3 in the 2.80 g sample and divide it by the total mass of the sample. Here's how you can do it step-by-step:
Step 1: Calculate the number of moles of Fe2O3 in the 2.80 g sample.
We first need to determine the molar mass of Fe2O3:
Fe2O3 = 2 * Fe + 3 * O = 2 * 55.85 g/mol + 3 * 16.00 g/mol = 159.7 g/mol
The number of moles of Fe2O3 can be calculated using the formula:
moles = mass / molar mass
moles of Fe2O3 = 2.80 g / 159.7 g/mol
Step 2: Calculate the number of moles of Fe2+ formed in the 25.0 mL aliquot.
Since the Fe2+ solution required 26.4 mL of a 0.0200 M K2Cr2O7 solution for complete oxidation, we can use the stoichiometry between Fe2+ and K2Cr2O7 to determine the number of moles of Fe2+:
0.0200 M K2Cr2O7 = moles of K2Cr2O7 / volume of K2Cr2O7 solution (in L)
moles of K2Cr2O7 = 0.0200 mol/L * (26.4 mL / 1000 mL/L) = 0.000528 mol
Since the stoichiometry is 6 moles of Fe2+ : 1 mole of K2Cr2O7, we can calculate the moles of Fe2+:
moles of Fe2+ = 6 * moles of K2Cr2O7 = 6 * 0.000528 mol
Step 3: Calculate the total moles of Fe2O3 in the ore.
Since the aliquot represents 1/10th of the total volume, we need to multiply the moles of Fe2+ by 10 to get the moles of Fe2O3 in the entire sample:
total moles of Fe2O3 = 10 * moles of Fe2+
Step 4: Calculate the mass of Fe2O3 in the ore.
mass of Fe2O3 = total moles of Fe2O3 * molar mass of Fe2O3
Step 5: Calculate the percentage of Fe2O3 in the ore.
percentage of Fe2O3 = (mass of Fe2O3 / total mass of sample) * 100
Now, you can substitute the values into the above equations to calculate the required percentage.
To calculate the percentage of Fe2O3 in the ore, we need to determine the moles of Fe2O3 in the 2.80 g sample. We can then use this information to find the molar mass and calculate the percentage.
First, let's find the moles of Fe2O3. The formula for Fe2O3 tells us that there are 3 moles of Fe for every 2 moles of Fe2O3. Thus, the moles of Fe2O3 can be calculated using the following conversion:
moles of Fe2O3 = (mass of Fe2O3 / molar mass of Fe2O3)
The molar mass of Fe2O3 can be calculated by adding up the atomic masses of Fe and O:
molar mass of Fe2O3 = (2 * atomic mass of Fe) + (3 * atomic mass of O)
Using the provided atomic masses (Fe = 55.85 g/mol and O = 16.00 g/mol):
molar mass of Fe2O3 = (2 * 55.85 g/mol) + (3 * 16.00 g/mol)
Next, we can calculate the moles of Fe2O3 by substituting the values into the previous equation.