A student mixed 15.0 mL of a solution of 0.0200 M ferric chloride FeCl3, with 25.0 mL of water.
Calculate the moles of iron ion, Fe +3 in the resulting solution.
(I think this is a Dilution problem, but I wasn't really sure how to start it out. Any help would be greatly appreciated.)
Here is what I started off with, but then I got confused:
M= moles solute/ 1 L solution
Moles of solute = (M)(1 L solution)
Moles Fe +3 = (0.0200M)(0.015L)
= 0.0003
Can I receive some clarification please? :) Thank you.
Assuming the volumes are additive (that is, is 15.0 + 25.0 = 40.0 mL), then
0.0200 x (15.0/40.0) = ?M
Or you can use the dilution formula as follows:
15.0*0.0200 = 40.0*M
M = 15.0*0.0200/40.0.
Same answer either way.
If you had followed through with your work you were headed in the right direction.
moles Fe^3+ = M x L = 0.02 x 0.015L = 0.0003 moles.
Then M of new soln = mol/L = 0.0003/0.040L = 0.0075 M. See if this is the same answer as both of the two above.
Wouldn't I just leave the answer as 0.0003 moles since the question is asking for the amount of the moles of the iron ion Fe +3 ? :) That's when I got confused.
You are right and I am wrong. Your remark about being a dilution problem started my mind in the direction of molarity and I went in that direction. However, you are absolutely right, moles is what the problem asks you do do and M x L = 0.0003 moles is correct.
Thanks so much for your feedback! :)
Certainly! You're on the right track with the formula for calculating moles of solute:
Moles of solute = (M)(volume of solution)
In this case, the solute is FeCl3 and the volume of solution is 15.0 mL. However, there is a slight correction needed in your calculation. You used a volume of 0.015 L, which is equal to 15.0 mL, but forgot to include the factor of 3 since ferric chloride has 3 chloride ions associated with each Fe+3 ion.
Here's the corrected calculation:
Moles of Fe +3 = (0.0200 M FeCl3) x (0.0150 L solution) x (1 mol FeCl3 / 1 L) x (1 mol Fe+3 / 1 mol FeCl3)
To explain this step by step:
1. First, we multiply the concentration of FeCl3 (0.0200 M) by the volume of the solution (0.0150 L) to get the number of moles of FeCl3.
2. Next, we multiply by the molar ratio (1 mol FeCl3 / 1 L) to convert from liters of solution to moles of FeCl3.
3. Finally, we multiply by the molar ratio (1 mol Fe+3 / 1 mol FeCl3) to convert from moles of FeCl3 to moles of Fe+3.
Doing the math, we get:
Moles of Fe +3 = (0.0200)(0.0150)(1)(1) = 0.00045 moles Fe +3
So, the moles of iron ion, Fe +3, in the resulting solution is 0.00045 moles.