Question

I'm a high school student who decided to investigate the relationship between caffeine concentration and brewing temperature of coffee out of their love for the substance. For my method, I opted for iodometric back titration, as detailed in this paper and shown in the image below. I've verified the method is viable with a known concentration of caffeine obtained by using caffeine tablets, but I am struggling to repeat the results on brewed coffee. When performing iodometric back titration on brewed coffee (as opposed to pure caffeine solution) with starch as an indicator, the end point isn't clearly defined because it is no longer colorless due to the natural brown pigments in brewed coffee.

I've looked into several potential routes that could help me mitigate the issue (detailed below), but I'm looking for advice on the most convenient (requiring the least time, resources, and skills) way to proceed. Of course, I'd like to maintain a certain level of quality, but it isn't as vital.

Answer 1

To mitigate the issue of the brown color in brewed coffee affecting the end point in the iodometric back titration, you can use a different indicator such as potassium iodide or opt for a spectrophotometric titration method.

Step-by-step explanation:

When performing the iodometric back titration on brewed coffee, the natural brown pigments in the coffee make it difficult to clearly define the end point. To mitigate this issue, you can use a different indicator that is not affected by the brown pigments in coffee.

One possible indicator to use is potassium iodide (KI), which forms a brown solution with iodine (I2). This brown solution can be titrated with sodium thiosulfate (Na2S2O3), which converts iodine to iodide. As you approach the end point, the brown solution will fade to a pale yellow color.

Another option is to use a spectrophotometric titration. This method involves measuring the absorbance of the coffee solution at a specific wavelength using a spectrophotometer. As the concentration of caffeine decreases during the titration, the absorbance will decrease, allowing you to determine the end point.