a potassium dichromate is prepared by 0.3525grams of K2Cr2O7 is enough water to yield 250.0mL of solution. a student then measures 10.00mL of an unknown solution of Fe2+ into an erlenmeyer flask and dilutes with 90mL of 1.0M hydrochloric acid. she then titrates this sample with the solution prepared above. if 38.40mL of the potassium dichromate solution is needed to reach the end point, what is the concentration of Fe2+ in the original unknown solution?

Question

a potassium dichromate is prepared by 0.3525grams of K2Cr2O7 is enough water to yield 250.0mL of solution. a student then measures 10.00mL of an unknown solution of Fe2+ into an erlenmeyer flask and dilutes with 90mL of 1.0M hydrochloric acid. she then titrates this sample with the solution prepared above. if 38.40mL of the potassium dichromate solution is needed to reach the end point, what is the concentration of Fe2+ in the original unknown solution?

Answer 1

To find the concentration of Fe2+ in the original unknown solution, we can use the concept of titration. Here's how we can solve this problem step by step:

Step 1: Calculate the number of moles of potassium dichromate used.
First, calculate the molar mass of K2Cr2O7:
K2Cr2O7 = (2 * atomic mass of K) + (2 * atomic mass of Cr) + (7 * atomic mass of O)
= (2 * 39.10 g/mol) + (2 * 52.00 g/mol) + (7 * 16.00 g/mol)
= 294.18 g/mol

Next, convert the given mass of K2Cr2O7 to moles using its molar mass:
0.3525 g / 294.18 g/mol = 0.0012 mol

Step 2: Find the number of moles of Fe2+ used in the titration.
From the balanced chemical equation of the reaction between K2Cr2O7 and Fe2+:

6 Fe2+ + Cr2O7^2- + 14 H+ → 6 Fe3+ + 2 Cr3+ + 7 H2O

We can see that 1 mole of K2Cr2O7 reacts with 6 moles of Fe2+.

Therefore, the number of moles of Fe2+ used can be calculated as follows:
0.0012 mol K2Cr2O7 x (6 moles Fe2+ / 1 mole K2Cr2O7) = 0.0072 mol Fe2+

Step 3: Calculate the molarity of Fe2+ in the original unknown solution.
First, calculate the volume of the Fe2+ solution used in the titration:
10.00 mL + 90.00 mL = 100.00 mL = 0.1000 L

Next, use the following formula for molarity:
Molarity (M) = moles of solute / volume of solution (in liters)

Molarity of Fe2+ = 0.0072 mol / 0.1000 L = 0.072 M

Therefore, the concentration of Fe2+ in the original unknown solution is 0.072 M.

Answer 2

mols K2Cr2O7 = grams/molar mass

Then M = mols/L solution.

You can use this information to calculate the concn of the Fe^2+ in the 10.00 mL sample of unknown ferrous solution BUT you won't now the concn of the original without knowing what the original volume was.