Ultraviolet (UV)-visible (Vis) spectroscopy is widely used in all modern laboratories as a routine method of analysis. The monitoring of chemical reactions in an aqueous solution involving a gas product is a demanding task but particularly for oscillatory reactions which are obtainable in a narrow concentration range. In this work, the optimization of experimental conditions for UV-Vis measurements of the Bray-Liebhafsky (BL) oscillatory reaction producing oxygen was done by using an internal standard. After applying the method of the internal standard on iodine absorbance at 460 nm, the characteristic BL oscillatory parameters (and iodine changes) are clearly evident. The obtained results allow students to apply their existing knowledge and, through a simple experimental setup, understand the importance of the internal standard, but at the same time, they show how they can solve the problem of UV-Vis noise during the time-based measurements of reactions involving gas products in general.