[Cheerios]

This question is on the experiment "Estimation of iron(II) in an iron tablet using a standard solution of potassium manganate(VII)".

Here is the question:


And here is my answer:
Acid: Va = 25.0cm^3 Ma = ? Na = 5
Base: Vb = 18.75cm^3 Mb = 0.01 Nb = 1

(i) (18.74 x 0.01 x 5)/(25 x 1)
= 0.03748 (0.0375)

(ii) 0.03748 x 56 (Mr of Fe2+) = 2.09888 (2.1)
2.09888 ÷ 4 = 0.52472 (0.525)

(iii) 0.525 /(0.325 x 5) x 100%
= 32.3%


I did this question 2 years ago and I'm revising it at the moment. I think the answers are all correct but I can't remember why I divided 2.09888 by 4 (in part ii) and where I got 0.325 (in part iii).

Can someone help me please?

[Borek]

Now you know why it is so important to write units.

0.325 looks like 0.325 g - mass of a tablet.

Some of these integer conversion factors are most likely related to the procedure - you started with some volume, but titrated only part of the solution. Not knowing details it is hard to comment without guessing.

[Cheerios]

You're right! I just noticed the 0.325g in the actual question itself (part C). Man, I'm blind. Thanks!

There are some examples in my book that are similar to the question in my original post and the workings/answers provided don't have anything divided by 4. Eh, maybe my answers were wrong.

Thanks again for your *delete me*

EDIT: Apparently I can't say help? Okay... Thank you for your assistance.

[Borek]

Got it. Its should be not /4 but ×0.25 (concentration of Fe²⁺ times volume of the solution, 250 mL = 0.25 L = 1/4 L). In terms of the final result these are equivalent operations.

[Cheerios]

Thank you, Borek! You've helped me a lot!