So there's this prelab assignment we're supposed to complete where we would fill out this table with [FeSCN^2+] in each of the test tubes. I'm not completely sure on how to do this?

For example, on the first tube calculate the molarity of [FeSCN^2+] with the data given:

-Volume of 1.25x10^-4M Fe(NO3)3 mL: 0.50

-Volume of 1.0M KSCN mL: 2.50

-Volume of 0.10M HNO3 mL: 2.00

-Calculated [FeSCN^2+] M: ???

What's the total volume? That's 0.50 + 2.50 + 2.00 mL = 5.00 mL.

How many mols FeSCN^2+ do you have? That's mols = M x L = 1.25E-4 x 0.0005 = ? (You're assuming here that the formation constant for FeSCN^2+ is so large that the reaction goes so far to the right that there is no Fe(NO3)3 left and all has been converted to the complex ion). Of course the Fe(NO3)3 is the limiting reagent.

Finally, M = mols/L. You have total mols and total L. Calculate M of the complex ion.

To calculate the molarity of [FeSCN^2+] in the first test tube, you need to use the provided data and apply the principles of stoichiometry. Here's how you can approach it step by step:

Step 1: Convert the volumes of the solutions to liters:
- Volume of 1.25x10^-4M Fe(NO3)3 mL: 0.50 mL = 0.0005 L
- Volume of 1.0M KSCN mL: 2.50 mL = 0 .0025 L
- Volume of 0.10M HNO3 mL: 2.00 mL = 0.002 L

Step 2: Determine the number of moles of each reactant using the given molarities and volumes:
- Moles of Fe(NO3)3 = molarity x volume = 1.25x10^-4M x 0.0005 L = 6.25x10^-8 moles
- Moles of KSCN = molarity x volume = 1.0M x 0.0025 L = 0.0025 moles
- Moles of HNO3 = molarity x volume = 0.10M x 0.002 L = 0.0002 moles

Step 3: Determine the limiting reactant (the reactant that is completely consumed) by comparing the moles of Fe(NO3)3 and KSCN. Since Fe(NO3)3 has fewer moles (6.25x10^-8), it is the limiting reactant.

Step 4: Use the stoichiometry of the reaction to calculate the moles of FeSCN^2+ formed. The balanced equation for the reaction is:
Fe(NO3)3 + 3KSCN → Fe(SCN)3 + 3KNO3

Since the stoichiometry ratio between Fe(NO3)3 and Fe(SCN)3 is 1:1, the moles of FeSCN^2+ formed will be equal to the moles of Fe(NO3)3 used.

Step 5: Calculate the molarity of [FeSCN^2+] in the first test tube:
- Molarity = moles/volume (in liters) = moles of FeSCN^2+ / total volume of the solution (in liters)
- In this case, the volume of the solution is the sum of the volumes of all the components added together (0.0005 L + 0.0025 L + 0.002 L = 0.005 L)
- Molarity = 6.25x10^-8 moles / 0.005 L = 1.25x10^-5 M

So, the calculated molarity of [FeSCN^2+] in the first test tube is 1.25x10^-5 M.