Predict the effect (Increase, Decrease, No effect, Indeterminate)and explain why

Question

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

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

Answer 1

1. OK although I don't know about the violet color. Most of the EDTA titrations for hardness go through a slight violet color just before they turn completely blue [they start red, go to violet(a mixture of red and blue), then to blue] so I don't know that I could attribute the violet color to iron. However, you are correct that the results would be high because Fe will require more of the titrant; i.e., it will titrate Fe along with calcium and magnesium.
2&3. I don't understand either of these.
4. Addition of starch too early in the titration forms an irreversible starch-iodine complex with the iodine that is not decolorized at the end point. Thus the end point will never be reached. Technically, I suppose this would give high results for Cu; however, personally I would prefer the answer of indeterminate since the value of Cu could be any number you chose. Anyway, this is what goes on; you decide which of the four choices to use as an answer.I don't think your explanation will fly.

Answer 2

analyical chemister ( skoog, west..) Chapter 11 (11-33) a,b,c