A piece of iron wire weighs 2.225g. It is dissolved in acid, which oxidizes the iron to iron(II), and made up to 250 mL. A 25mL sample required 31.0 mL of a 0.0185mol/L solution of potassium dichromate. Calculate the percentage of iron in the wire.
To calculate the percentage of iron in the wire, we need to find the number of moles of iron and the molecular weight of iron.
1. Calculate the number of moles of potassium dichromate used:
- The volume of the potassium dichromate solution used is 31.0 mL.
- The concentration of the solution is 0.0185 mol/L.
- Use the formula: moles = concentration × volume.
- Therefore, moles of potassium dichromate = 0.0185 mol/L × 0.0310 L.
2. Calculate the number of moles of iron:
- By balancing the chemical equation between iron and potassium dichromate, we know that 6 moles of potassium dichromate (K2Cr2O7) react with 6 moles of iron (Fe).
- Therefore, moles of iron = moles of potassium dichromate.
3. Calculate the molecular weight of iron (Fe):
- The atomic weight of iron is 55.845 g/mol.
4. Calculate the weight of iron in the wire:
- Use the formula: weight = moles × molecular weight.
- Therefore, weight of iron = moles of iron × molecular weight of iron.
5. Calculate the percentage of iron in the wire:
- Use the formula: percentage = (weight of iron / weight of wire) × 100.
- Therefore, percentage of iron = (weight of iron / 2.225 g) × 100.
Plug in the values to obtain the final answer.