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[Audio] What substance? Propanoic acid 3000 2000 1500 1000 500 Wavenumber -1-1-0-0 50 0 Transmittance % Bond Functional groups containing the bond Typical infra-red absorption range (in wavenumbers)/cm –1 C = O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 O — H carboxyl hydroxy 2500–3000 3200–3600 Carboxylic acids have strong and very broad peak at 2500-3-0-0-0 Let's examine the infrared (I-R---) spectrum to identify the substance present. The graph displayed here shows a characteristic IR absorption spectrum, and the table on the left provides us with typical absorption ranges for different functional groups. Looking at the spectrum, we can observe a strong and broad peak between 2500 and 3000 centimeters⁻¹. This range is indicative of the O–H stretch found in carboxylic acids. In fact, this strong, broad peak is a signature feature of carboxylic acid groups. Additionally, there’s a peak around 1700 centimeters⁻¹, which corresponds to the C=O stretch commonly found in carboxyl groups. These combined peaks—the broad O–H stretch and the sharp C=O stretch—strongly suggest that the compound we’re analysing is propanoic acid, which is a carboxylic acid.