Benedict's weirdness

Discussion in 'Supporting Biology' started by bigmeankitty, Feb 14, 2020.

  1. I have two batches of Benedict's reagent currently, Batch A I made, is about five months old, used right after being made, worked perfectly. We tried using it again this week, and there was some white precipitate in the bottle and when I drew some up into a teat pipette, it turned quite purple.

    Now, my school is janky and reuses plastic teat pipettes until they split, and I've read about Benedict's reacting weakly with protein like biuret, so I wondered if the pipette was contaminated with something. I mixed the Benedict's with the hydrolysed sucrose solutions to see if it would still react, and all concentrations (1.0M, 0.5M, 0.25M, 0.125M) instantly turned reddish purple with no heat applied :confused::confused:

    On to Batch B, found in the back of the cabinet, I don't know who made it or how long ago (>9 months for sure), no precipitate. We repeated the lab with Batch B today after school. No purple, the color changes didn't happen until after heat was applied, but only the 1.0M changed color (brick red), the 0.5M stayed clear blue with a very small amount of red precipitate, and 0.25M and 0.125M absolutely no change?

    So, I'm confused. I'm a math teacher, I'm teaching CIE AS Biology because there was a staffing hole and I did my undergrad in bio, but troubleshooting in the lab is not my specialty at all. I'm leaning toward this having something to do with age and poor storage. Our lab is beyond under-resourced (I'm in Eastern Europe), and both batches were stored in clear, thin plastic bottles inside of dark cabinets. We have all the ingredients for more Benedict's, and it's hard to source chemicals here, so I'd prefer to make another batch over ordering, but obviously only if I can figure out how to ensure it works properly as it often pops up on the practical examination. Any thoughts?
    Last edited: Feb 14, 2020
  2. Sounds like a storage issue to me, although my life has been plagued the last year with non-functional Benedict's reagent. Whereabouts in Eastern Europe?
    Last edited: Feb 18, 2020
  3. Well thats a hefty mystery

    Lets start at the beginning I suppose, what are your recipe's used for making both batch A and B?