After a precipitate forms, how is it isolated?

• A. Filter the solution to get the precipitate onto filter paper
• B. Boil the mixture to dissolve the precipitate
• C. Allow it to stand and crystallize slowly without separation
• D. Decant the liquid and discard the solid

Answer: (A)

Isolating a precipitate means separating the solid that formed from the liquid it came from. Filtration does this effectively: pouring the mixture through filter paper lets the liquid pass through while the solid precipitate is trapped on the paper, so you can wash and dry it to obtain the isolated solid.

Boiling would either dissolve the precipitate back into solution or just heat the mixture without separating the solid cleanly. Letting it stand to crystallize doesn’t separate the solid from the liquid, and decanting would leave the solid behind or could discard the solid along with the liquid. Filtration is the standard method for this separation.