[rentj]

I had a practical exam today, which I create solutions of glucose with different concentrations (0%, 0.25%, 0.5%, 1%, 1.5% and 2%), put Benedict's reagent, and observe the color change. In each test tube, I added 1 mL of the solution and 2 mL of the Benedict reagent, total of 3 mL. And then I heated the test tube in a water bath at 50-60 deg C until I observe a color change. The result is attached, where the top one is 2%, 1.5%, 1%, 0.5%, 0.25%, and 0% (very bottom). I expected a color change from blue to red (green, yellow, orange) for each glucose solution, however only red precipitate that appears in my test tube. Besides that, my peers' result showed the expected result (the color gradient). What could be the error behind my result? Thank you.

[Borek]

Don't think I have ever worked with the Benedict's reagent, but in general I see nothing wrong with your samples. Seems like the amount of precipitate is higher for the samples with higher amount of glucose, which is what is expected. Colors that appear during the procedure are probably intermittent - as the precipitate ages (it can need just minutes to do so in general, no idea about this specific case) particles of the precipitate grow on average (more precisely: smaller ones disappear, larger ones get larger) and settle down, leaving just the blue solution.