Question

As shown in the figure below, EBT solution is blue when pH is adjusted to 10. When calcium chloride is added to EBT solution, the color turns red due to the formation of EBT-metal complex. If you use your standard EDTA solution to titrate/quantify a calcium chloride (CaCl2) solution with unknown concentration, what is the color of the solution at end point?

Answer 1

The color of solution at the end point will be blue.

Step-by-step explanation:

EBT is used as an indicator for complexometric titrations and acts as a chelating agent. It has a blue color, in its free form, when the pH is adjusted to 10.

On the addition of CaCl₂, EBT binds with Ca(II) and gives a red color, due to its EBT-Ca (II) complex. So, the color at the start of the titration is red.

When EDTA is added, it starts to form EDTA-Ca(II) complex. Near the endpoint, it starts to replace EBT bound to Ca, because it has a higher formation constant (Kf) for its EDTA-Ca(II) complex than EBT-Ca(II) complex. The EDTA-Ca(II) has no color so the solution shows the colour of free EBT, which is blue. Hence the color at the endpoint will be blue.