Science practice 91

PASSAGE VI

Certain preservatives known as sulfites are often added to fruit products to keep the fruit fresher longer. Use of sulfites is controversial because studies have linked sulfites to severe reactions in some asthmatics. Students performed 2 experiments to measure sulfite levels.

Experiment 1

Four solutions, each containing a different amount of sulfite dissolved in H₂O were prepared. A coloring agent was added that binds with sulfite to form a red compound that strongly absorbs light of a specific wavelength, and each solution was diluted to 100 mL. A blank solution was prepared in the same manner, but no sulfite was added. A colorimeter (a device that measures how much light of a selected wavelength is absorbed by a sample) was used to measure the absorbance of each solution. The absorbances were corrected by subtracting the absorbance of the blank solution from each reading (see Table 1 and Figure 1).

Figure 1

Experiment 2

A 100 g fruit sample was ground in a food processor with 50 mL of H₂O and the mixture was filtered. The food processor and remaining fruit were then washed with H₂O, these washings were filtered, and the liquid was added to the sample solution. The coloring agent was added and the solution was diluted to 100 mL. The procedure was repeated for several fruits, and the absorbances were measured (see Table 2).