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No Color Change During Manual Titration
znaes97:
Hello,
I am attempting to perform a titration to determine the concentration of sodium dichromate in a nitric acid bath. The titration is done in two steps. The first step is to titrate (with 0.1N sodium thiosulfate) to a straw yellow color. Once this change occurs, you are supposed to add starch indicator and continue titrating until a clear-green endpoint is reached. My problem is that I am not seeing any color change to straw yellow during the first step. Does this mean that there is little to no sodium dichromate in the solution? Before titration, the solution is prepared with 20% potassium iodide and a few mLs of concentrated HCl. The final result should only be a few mL, but I titrated ~25mL without seeing any changes. Any help or suggestions are greatly appreciated. Thanks in advance
Borek:
Can you elaborate on the procedure you are following?
znaes97:
--- Quote from: Borek on October 19, 2022, 06:02:34 PM ---Can you elaborate on the procedure you are following?
--- End quote ---
The full procedure is as follows:
1. Pipette a 1ml sample into a 250ml Erlenmeyer flask
2. Add 150ml of DI water
3. Add 10ml of concentrated HCl
4. Add 5ml of 20% potassium iodide solution
5. Titrate with 0.1N sodium thiosulfate to a straw color
6. Add 2ml of starch indicator and continue titrating to a clear light green color
% by weight sodium dichromate = ml of sodium thiosulfate used * 0.498
The target concentration is 2.0 - 2.5%
Borek:
--- Quote from: znaes97 on October 19, 2022, 01:20:11 PM ---The first step is to titrate (with 0.1N sodium thiosulfate) to a straw yellow color.
--- End quote ---
What is the initial color of the solution?
znaes97:
--- Quote from: Borek on October 20, 2022, 11:56:35 AM ---
--- Quote from: znaes97 on October 19, 2022, 01:20:11 PM ---The first step is to titrate (with 0.1N sodium thiosulfate) to a straw yellow color.
--- End quote ---
What is the initial color of the solution?
--- End quote ---
The initial color of the solution was clear. When adding the potassium iodide, I dimmed the lights and the solution appeared to be very faintly yellow, but when I turned the light back up, the solution appeared to change from faint yellow to clear.
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