Video summary

OXIGENO DISUELTO POR METODO WINKLER

Main summary

Key takeaways

Science and Nature

Scientific Concepts / Phenomena Presented

  • Determination of dissolved oxygen (DO) using an indirect chemical method (not electronic/sensor-based).
  • Winkler method (Winter alternative method): an established technique accepted by regulations when a dissolved-oxygen probe (membrane electrode) or an oximeter is not available.
  • Chemical “fixation” (chemical preservation) of oxygen in the field
    • DO is transformed from a volatile oxygen form into stable reaction products via reagents added immediately after sampling.
    • The sample is then preserved using cold-chain physical preservation (refrigeration, not freezing) until lab analysis.
  • Colorimetric indicators as evidence of oxygen presence
    • After reagent additions, color changes act as a qualitative/indicator response.
    • Expected behavior:
      • With oxygen present: characteristic yellow/honey-yellow outcome.
      • Without oxygen: the sample tends to become milky/white and may form a white precipitate after later reagents.
  • Titration-based quantitative measurement
    • After adding reagents (including starch indicator), an endpoint titration is performed.
    • The progressive color transitions during titration are used to identify the final endpoint.
    • The amount of titrant used (given as sodium thiosulfate, 0.025 N) is used to calculate dissolved oxygen.
  • Stoichiometric calculation / Universal Titration Equation
    • Uses a proportionality relationship (shown as B1·c1 = a·b2·C2) to compute oxygen from titrant volume, normality, and sample volume.

Methodology / Procedure Outlined (Winkler DO, Indirect)

Sampling Setup (Field)

  • Use a Winkler bottle (300 mL capacity, ground-glass neck, stopper).
  • Submerge the sealed bottle in the water body so it becomes fully filled.
  • Loosen the stopper to allow filling; discard water remaining in the conical section.
  • Turn the bottle upside down and ensure no air bubbles remain (critical to success).

Transport and Reagent Preservation (Field Chemical Reagents)

  • Transport reagents separately.
  • For each 300 mL Winkler bottle, add:
    • 1 mL manganese sulfate
      • Produces a slight pinkish color (manganese-related).
    • 1 mL “acid iodide” (iodide reagent)
      • Causes the sample’s appearance to change completely (indicating oxygen presence).
    • 1 mL concentrated sulfuric acid
      • Produces a honey-yellow color if oxygen was present.
      • If oxygen was absent: milky/white appearance and potentially a white precipitate.

Cold-Chain / Physical Preservation

  • Keep the fixed sample refrigerated (not frozen).
  • Follow the standard maximum permissible holding time before lab analysis.

Lab Titration

  • Measure 100 mL of the preserved sample into a 250 mL container.
  • Add starch indicator (a few drops; described as slightly diluted and milky).
    • Endpoint chemistry yields a dark coloration upon oxygen-related reaction.
  • Perform titration using an electronic burette with sodium thiosulfate (0.025 N).
  • Observe indicator/color change progressively until it becomes colorless (titration endpoint).
  • Record titrant volume at endpoint (example values given around 4.19 mL).
  • Compute dissolved oxygen using the stoichiometric relationship (Universal Titration Equation).

Researchers / Sources Featured (Named)

  • Winkler: the researcher/patent origin referenced for the Winkler bottle and method context.

Original video