When the pH of the solution equals the pKa of an indicator, the solution will have an intermediate color. Estimate the pKa of bromocresol green, the indicator that made the transition in the acidic region of the titration.

pKa bromocresol green is ≅4.5

Explanation:

The bromocresol green is a chemical indicator used in titrations with equivalence point at pH's between 3 and 5.

Is an indicator that, in acidic region is yellow, and in basicic region is blue. The intermediate color is green (at pH≅ 4.5).

As at the intermediate color of the indicator pKa = pH,

pKa bromocresol green is ≅4.5

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na