What result does a pure substance produce during paper chromatography?

A pure substance produces one distinct spot during paper chromatography because it contains only a single type of molecule. This characteristic allows for the separation of components based on their different affinities for the stationary phase (the paper) and the mobile phase (the solvent). When a pure substance is subjected to the chromatography process, it does not interact with the stationary phase in varying degrees, leading to the formation of just one spot at a specific location on the paper. This single spot corresponds to the unique Rf value (retention factor) for that pure compound, indicating its identity.

In contrast, mixtures of substances would produce multiple spots as each component travels at a different rate up the paper, leading to the appearance of several distinct spots. No spots would indicate that no substance has been detected, which does not apply to pure substances introduced in this experiment. Multiple overlapping spots imply that various substances are present and have not been adequately separated in the mixture.