When ozone reacts with an excess of potassium iodide solution buffered with a borate buffer (pH 9.2) — Qualitative and Quantitative Analysis Chemistry Question
Question
When ozone reacts with an excess of potassium iodide solution buffered with a borate buffer (pH 9.2) iodine is liberated which can be titrated against a standard solution of sodium thiosulphate, this is a quantitative method for estimating O3 gas. When liberated I2 and sodium thiosulphate will react, then product is/are :
💡 Solution & Explanation
Step 1: The reaction of bismuth(III) ions with iodide ions (I-) initially forms a dark brown/black precipitate of bismuth(III) iodide (BiI3). Step 2: The black BiI3 precipitate reacts with excess iodide ions to form a highly stable, soluble tetraiodobismuthate(III) complex anion: BiI3 + I- -> [BiI4]-. Step 3: The [BiI4]- complex solution exhibits a characteristic orange/yellow-orange color. This confirms the presence of Bi3+, matching option (b).