Question

In an experiment, solid lead iodide is produced in a mixture with a solution of a soluble salt. How can a pure, dry sample of solid lead iodide can be obtained from this mixture?

Answer 1

`Pb(NO_3)_2 + 2I^(-) rarr PbI_2(s)darr + 2NO_3^-`
By suction filtration, and prolonged drying.

Explanation:

Lead halides are VERY insoluble. When halide ion is added to a solution of a soluble lead salt (say `Pb(NO_3)_2` or `Pb[(O(O=)C-CH_3]_2`, a precipitate of `PbX_2` occurs. Lead halides are very insoluble, and MOST of the `Pb^(2+)` is present in the precipitate.

The lead halide is then transferred to a Buchner funnel for suction filtration (of course we use the filtrate, already saturated with the lead salt to help us with the transfer, and sluice the salt of the reaction flask). The precipitate is washed a couple of times with fresh solvent, and then subjected to prolonged suction and drying, by drawing air thru the sample. Given enough patience, a dry free-flowing powder can be obtained (sometimes the precipitate is washed with ethanol to facilitate drying).