Video narration
In this lab practical, what does a colour change in the tube actually tell you? First, check your lab's validated procedure: heating Benedict's reagent before adding urine, as some instructions state, is unusual. In the usual sequence, measure 5 millilitres of Benedict's reagent into a tube, add eight drops of urine, then heat for 5 to 10 minutes, following lab safety instructions. Let the reaction finish, and compare the final colour-not the starting liquid-with your practical's chart. Blue means absent. Green with a slight yellow precipitate is trace; green with a thicker yellow precipitate is 1+. Yellow to orange precipitate is 2+; orange to red, 3+; and brick red, 4+. These grades follow the supplied scale, not exact concentrations. So what does the tube tell you? It suggests how much reducing sugar is present, but Benedict's test does not identify glucose specifically.