[People]

Hi,

We have titrated the liberated iodine with Titrant for determination of amount of Fe2O3. But we have used about 35 mL for titrant. So when we calculated  the percentage of ferric oxide,we found %18. We have to multiply with 5, if we want to find the results %100. Please can you write rections in every steps?

Thank you
 



 
Sample: 1.5 g
 
Blank: 25 mL of hydrochloric acid
 
Titrimetric system 
Mode: Direct titration
 
Titrant: 0.1 N sodium thiosulfate VS
 
Endpoint detection: Visual
 
Analysis: Digest the Sample in 25 mL of hydrochloric acid on a water bath until dissolved. Add 10 mL of hydrogen peroxide TS, and evaporate on a water bath almost to dryness to volatilize all hydrogen peroxide. Dissolve the residue by warming with 5 mL of hydrochloric acid; add 25 mL of water; filter into a 250-mL volumetric flask, washing the filter with water; and add water to volume. 

Transfer a 50-mL aliquot to a glass-stoppered flask, add 3 g of potassium iodide and 5 mL of hydrochloric acid, and insert the stopper into the flask. Allow the mixture to stand for 15 min, add 50 mL of water, and titrate the liberated iodine with Titrant, using starch TS as the indicator. Perform a blank determination in the same manner.
 

Calculate the percentage of ferric oxide (Fe2O3) in the portion of the sample taken:
 
Result = {[(VSVB) ×N×F]/W} × 100
 
VS = = Titrant volume consumed by the Sample (mL)
VB = = Titrant volume consumed by the Blank (mL)
N = = actual normality of the Titrant (mEq/mL)
F = = equivalency factor, 79.85 mg/mEq
W = = Sample weight, calculated with a correction for loss on ignition (mg)
   
Acceptance criteria: 97.0%–100.5% on the ignited basis

[Borek]

You have to show your attempts at solving the question to receive help. This is a forum policy.

[Golden_4_Life]

Borek:
Why is this analyst saying they must multiply the answer by "5" ?
18 x 5 = 90?
why 5 ?

[Borek]

Ask the OP, I have never suggested multiplying anything by 5.

[Golden_4_Life]

Ah! I had to re-read the post: their prep is 1/5 dilution of the stock test sample--hence the 5x.
Sometimes I amaze even myself