Summary
Highlights
The video defines solubility as the amount of solute in a solution at a given temperature. It then shows the mixing of potassium iodide and lead (II) nitrate solutions, which results in the precipitation of lead (II) iodide, a yellow solid with low solubility in water at room temperature. A dynamic equilibrium is established between the dissolved solute and the precipitate.
The experiment begins by decanting and washing the lead (II) iodide precipitate, then adding deionized water and heating the mixture. A hot saturated solution of lead (II) iodide is maintained near 100°C. Six empty test tubes are weighed, placed in a hot water bath, and 20 ml of the saturated solution is transferred into each, assuming equal amounts of dissolved solute.
The samples are placed in water baths at various temperatures: 97°C, 70°C, 50°C, 25°C, and 0°C (ice water bath). One sample is allowed to cool slowly to room temperature. As cooling occurs, yellow crystals of lead (II) iodide form and settle. After an hour, little to no solute crystallized at 97°C, while a substantial amount crystallized in the ice water bath, indicating lower solubility at lower temperatures.
To determine the amount of crystallized solute, the test tubes are quickly removed from their baths, decanted, and the residue dried. The mass of the dried lead (II) iodide is then calculated for each temperature. The results demonstrate that as temperature decreases, the mass of solute that crystallizes out of solution increases, confirming that lead (II) iodide solubility decreases with decreasing temperature. The video also notes that the rate of cooling affects crystal size but not the final solubility.