Refractive index measurement using an interferometric imaging system and observation of chemical wave shapes were carried out during chemical wave propagation of a cerium-catalyzed Belousov-Zhabotinsky (BZ) reaction. Densities increased as chemical waves propagated in samples without NaBr, and decreased in samples with NaBr. Concentration changes of malonic acid, bromomalonic acid, and BrO3- were estimated from Raman spectral measurements in a stirred batch BZ reaction, and these also exhibited differences between samples with and without NaBr. It is proposed that a reaction subset yielding low molecular weight carboxylic acids is predominant in samples with NaBr, whereas a pathway leading to dibromoacetic acid or tribromoacetic acid production is the major process in samples without NaBr.