Used as a reagent to detect carbonyl groups in aldehydes and ketones. When added to a compound containing a carbonyl group, it forms a yellow, orange, or red precipitate known as a dinitrophenylhydrazone. This color change helps identify the presence of such functional groups in qualitative organic analysis. Commonly used in undergraduate laboratory experiments and in pharmaceutical testing to characterize unknown compounds. Also applied in the purification and identification of carbonyl-containing substances due to the crystalline nature and sharp melting points of the derivatives formed.