Final answer:
The substance that precipitates first upon the addition of solid potassium hydroxide to a solution containing iron(III) nitrate and calcium acetate is iron(III) hydroxide (Fe(OH)3), due to its lower solubility product compared to calcium hydroxide.
Step-by-step explanation:
When solid potassium hydroxide (KOH) is added to a solution containing iron(III) nitrate and calcium acetate, the precipitate that forms first will depend on the respective solubility products (Ksp) of the potential hydroxide precipitates. Iron(III) hydroxide (Fe(OH)3) and calcium hydroxide (Ca(OH)2) are both possible precipitates. However, iron(III) hydroxide has a lower solubility product compared to calcium hydroxide, indicating it will precipitate first.
Potassium hydroxide dissociates in water to produce OH- ions, which can then combine with Fe3+ ions from iron(III) nitrate to form Fe(OH)3 as an insoluble solid. As the concentration of OH- increases due to the addition of KOH, the Ksp of Fe(OH)3 will be exceeded before that of Ca(OH)2, leading to the precipitation of Fe(OH)3 first.