Final answer:
Visually determining the excess use of EDTA in a titration based solely on color is not reliable. A sharp color change signals the end point, but a small excess of EDTA beyond that may not visibly alter the color further. Instruments like pH meters or spectrophotometers are needed for more precision.
Step-by-step explanation:
It is generally not possible to visually judge whether you've added an excess of EDTA (such as 1 drop or 1 mL extra) in a titration involving eriochrome black T as the indicator and looking for Ca2+ ions based solely on color.
This is because the color change will be very subtle and difficult for the human eye to detect with such a small excess of EDTA.
Choosing the correct indicator is crucial in titrations, as it must signal the end point effectively. In the case of titrating with EDTA and using eriochrome black T, the color change occurs at a specific pH range where the complexation reaction is complete.
If a sharp color change is obtained at the end point, adding 1 drop or 1 mL of excess EDTA beyond the end point might not produce an observable change in color without careful analytical techniques.
For more accurate determination of the end point, instrumentation such as a pH meter or a spectrophotometer could be used to detect the precise moment when the reaction has reached equivalence, since these devices are more sensitive than the human eye to small changes in concentration or color.