# 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

## 1. Condition: In the determination of water hardness, the water sample contained appreciable amount of ferric ions

Effect: Increase
Explanation: The presence of ferric ions in the water sample will increase the measured hardness of the water. This is because ferric ions can form insoluble complexes with carbonate ions (CO3^2-) present in the water, which contributes to the overall hardness. Therefore, the measured hardness in terms of ppm CaCO3 will increase.

2. Condition: Instead of MgCl2*H2O, CaCl2*xH2O was added to the EDTA titrant (determination of water hardness)
Effect: No effect
Explanation: The EDTA titrant is used to determine the hardness of water based on its ability to chelate metal ions. The choice of MgCl2 or CaCl2 does not affect the accuracy or efficiency of the chelation process. Both magnesium and calcium ions are divalent cations that can be complexed by EDTA. Therefore, replacing MgCl2 with CaCl2 in the titrant will not have any effect on the measured hardness in terms of ppm MgCO3.

3. Condition: Absence of MgCl2 in EDTA solution that was standardized (determination of water hardness)
Effect: Decrease
Explanation: The presence of MgCl2 in the EDTA solution is crucial for accurate standardization. Magnesium ions are used as the primary standard to calibrate the EDTA solution because their reaction with EDTA is precise and stoichiometric. Without magnesium ions, the EDTA solution cannot be accurately standardized. As a result, the volume of EDTA required to reach the endpoint will decrease, indicating a decrease in water hardness.

4. Condition: The starch solution was added at the start of the titration (quantitative determination of copper concentration in aqueous solution by iodometric titration)
Effect: Indeterminate
Explanation: The addition of starch solution at the start of the titration in an iodometric titration for copper determination does not affect the accuracy or precision of the method. Starch is commonly used as an indicator in iodometric titrations to detect the endpoint when all the copper ions have reacted with iodine. However, adding the starch solution at the start instead of near the endpoint may make it difficult to visually detect the color change accurately. Therefore, the effect on the calculated ppm Cu cannot be determined solely based on the addition of starch at the start.