AL chem:carbonyl cpd +NaHSO3,急

in fact, the reaction is as simple as that, need not too much details to describe.

for aldehydes (except ethanal and methanal) and methylketones, saturated NaHSO3 solution is added.
the addition product has low solubility in water, which leads to precipitation of solid/crystals. (the addition products of methanal and ethanal are, however, reasonably soluble in water, making separation difficult)
filter them out, wash, and do extra recrystallization if required.

the reaction between NaHSO3 and aldehydes / methylketones is reversible. heat the product in inorganic acid / alkali, which restores the original aldehyde/ketone. do a phase separation to obtain the aldehydes / ketones if wanted.