A UV-visible spectrometer was used to obtain the spectra of solutions of substances P and Q - HSC - SSCE Chemistry - Question 6 - 2022 - Paper 1

To determine the concentration of Q in a mixture of the two solutions, we need to identify a wavelength where the absorbance of Q is distinct and does not overlap significantly with that of P.

Examining the absorbance spectra:

• Solution P shows a peak around 410 nm, which is not suitable as it will interfere with Solution Q measurements.
• Solution Q has a significant peak at approximately 630 nm, where it has relatively higher absorbance values while Solution P shows a lower absorbance. Therefore, 630 nm is a clear choice as it allows for accurate measurement of the absorbance of Q without interference from P.

Thus, the most appropriate wavelength to determine the concentration of Q in the mixture is D. 630 nm.