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

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

Partially answered above at another post of the same question.

1. Increase: The presence of ferric ions in the water sample will indeed affect the determination of water hardness. Ferric ions can react with EDTA and form a violet-colored complex instead of the desired clear-blue complex at the endpoint. This means that the endpoint will be harder to detect, leading to the addition of more EDTA before the color change is observed. Since EDTA reacts with calcium ions to form a complex, adding more EDTA will result in an increased calculated ppm CaCO3. Thus, the effect is an increase in the determined water hardness.

2. Decrease: In the determination of water hardness, the standard method involves using MgCl2•H2O as the titrant (solution added to react with the analyte). However, if CaCl2•xH2O is used instead, it introduces calcium ions into the system that will react with the EDTA. This means that some of the EDTA will be consumed by the calcium ions added via CaCl2•xH2O. As a result, less EDTA will be available to react with the magnesium ions in the water sample, leading to a decrease in the determined ppm MgCO3 of the analyte solution.

3. Decrease: The presence of MgCl2 in the EDTA solution is crucial for the determination of water hardness. Magnesium ions react with EDTA during the titration process to form a complex, reaching a visible endpoint. In the absence of MgCl2, an endpoint may not be reached, or it may be reached prematurely. This will result in a lower volume of EDTA required to reach the endpoint, indicating a decrease in the determination of water hardness.

4. Increase: The addition of starch solution, usually as an indicator, at the start of the titration affects the determination of copper concentration in aqueous solution by iodometric titration. Starch forms a complex with the copper(II) ions, preventing them from reacting with iodine (I3-) that is used as the titrant. As a result, less iodine will react with the copper ions, leading to a lower consumption of Na2S2O4 titrant. Since Na2S2O4 is added until all the iodine is reacted, a decrease in the consumption of Na2S2O4 indicates that the concentration of copper ions is higher. Therefore, the effect is an increase in the calculated ppm Cu.