I am really having a hard time doing this question.

We were asked to determine the iron content of spinach in a solution.
We burned a 5.50g of spinach and added 10 ml of 2.0 M HCl in the spinach ashes. We mixed that and filtered the solution to removed the ashes. We used 5 ml of that solution and put it in a testube and added 5 ml of 1.5 M KSCN in the testube. We then use a spectrometer to determine its wavelenght, which is 0.178. I calculated the concentration and got 0.000023 M. We were asked to determine the mass of the iron in the spinach that we used , and determine the mg of iron per 100 g of spinach.

First I doubt you determined the wavelength. Probably the wavelength was set or you set it to some desired number. I suspect the 0.178 was the absorbance you read from the spectrometer. Any, one of that really matters.

So M = 2.3E-5 what? Is that 2.3E-5 M Fe. I will assume so. That is 2.3E-5 mols/L and that is 2.3E-5 mols x 55.85 g Fe/mol = approx 1.3E-3 g Fe/L or 1.3 mg Fe/L and that is in the final 5 mL sample you took to make the measurement. So mg Fe in the 5 mL measured sample is 1.3 mg Fe/L x 0.005 L = 6.5E-3 mg Fe. What mass spinach was in the 5 mL? That's 5.5 g/2 or 2.75 g. Now you have mg Fe in 2.75 g sample. Convert that to mg Fe in 100 g spinach.

Im not sure how to convert the mg Fe in 100 g of spinach.

Do i just multiply the mg Fe to 100 g or I have to divide the mg Fe by the spinach mass (which is 5.50 g before i burned it) and then multiply it by 100?

To determine the mass of iron in the spinach and the mg of iron per 100 g of spinach, we need to follow the steps:

Step 1: Calculate the moles of SCN^- ion used in the reaction.
Given that you used 5 mL of a 1.5 M KSCN solution, we can use the formula:

moles of SCN^- = concentration x volume
moles of SCN^- = 1.5 M x 5 mL x (1 L / 1000 mL) = 0.0075 moles

Step 2: Calculate the moles of Fe^3+ ion in the solution.
Using the balanced chemical equation: Fe^3+ + SCN^- → Fe(SCN)^2+, we know that the ratio of moles of Fe^3+ to moles of SCN^- is 1:1.
Thus, the moles of Fe^3+ ion is also 0.0075 moles.

Step 3: Calculate the mass of Fe^3+ ion.
Since Fe^3+ has a molar mass of 55.845 g/mol, we can use the formula:

mass = moles x molar mass
mass = 0.0075 moles x 55.845 g/mol = 0.41884 g

So, the mass of iron in the spinach that you used is 0.41884 g.

Step 4: Calculate the mg of iron per 100 g of spinach.
Given that you used 5.50 g of spinach, we can use the formula:

mg of iron per 100 g = (mass of iron / mass of spinach used) x 100
mg of iron per 100 g = (0.41884 g / 5.50 g) x 100 = 7.616 mg/100 g

Therefore, the spinach you used contains approximately 7.616 mg of iron per 100 g.