🔬 Understanding the Diagram:

The alpha diagram shows the relative abundance (% species) of different ionic forms of a polyprotic acid as a function of pH. In this case, the number of distinct curves (4 total) indicates the presence of 3 acidic protons.

• At low pH (0–2): One dominant species → fully protonated form: H₃A
• Around pH 3–5: Second species dominates → H₂A⁻
• Around pH 6–8: Third species dominates → HA²⁻
• At high pH (10+): Fully deprotonated species: A³⁻

Therefore, the acid releases 3 protons in stepwise fashion, confirming it is triprotic.

📍 What is the dominant species at pH 4?

At pH 4, the orange curve is the dominant peak. This corresponds to the second species, H₂A⁻, where one proton has been lost.