Homework Help: Analytical Chemistry

Posted by :kkk: on Friday, August 31, 2007 at 6:01am.

Predict the effect (Increase, Decrease, No effect, Indeterminate)and explain why
1. Condition:
In the determination of water hardness, the water sample contained appreciable amount of ferric ions
Paameter: ppm CaCO3
2. Condition:
Instead of MgCl2*H2O, CaCl2*xH2O was added to the EDTA titrant(determination of water hardness)
Parameter: ppm MgCO3 of the analyte solution
3. Condition:
Absence of MgCl2 in EDTA solution that was standardized (determination of water hardness)
Parameter: Volume of EDTA to reach endpoint
4. Condition:
The starch solution was added at the start of the titration (quantitative determination of copper concentration in aqueous solution by iodometric titration)
Parameter: calculated ppm Cu

Analytical Chemistry - Dr Russ, Friday, August 31, 2007 at 7:27am
Can I suggest that you post your thinking and we will comment on your answers.
Analytical Chemistry - :kkk:, Friday, August 31, 2007 at 9:24am
Here are my thoughts:
1. Increase, because ferric ions will cause the endpoint to become violet instead of a clear blue. Hence, greater amount of EDTA will be used thus increasing the calculated ppm CaCO3
2. I have no idea...
3. Decrease, because in the absence of MgCl2 in the solution, the endpoint comes too early. Hence, less of the EDTA titrant would be added.
4. Increase, since less of the I3- will be formed and less of the Na2S2O4 titrant would be needed. less Na2S2O4 used = higher Na2S2O4 concentration = higher Cu concentration = higher ppm Cu
- Analytical Chemistry - DrBob222, Friday, August 31, 2007 at 9:20pm
  Answered partially above at another of your posts.

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