Iodide Oxidation by Hydrogen Peroxide

  1. In my chemistry lab we prepared the following solutions:
    Buffered Iodide Solution
    25 mL acetic acid/sodium acetate buffer
    6mL of 0.5 % starch solution
    6 mL of 1.0M KI
    fill to the 250 mL mark with distilled water

    0.025M Thiosulfate Solution
    5 ml of 1 M Na2S2O3
    fill to the 200 ml mark with distilled water

    Peroxide Soution
    30ml of 1 M H2O2
    fill to the 150 ml mark with distilled water

    Then mixing these solutions together:
    Mixture 1:
    Buffered Iodide 40ml
    Thiosulfate Solution 10ml
    Distilled Water 10 ml

    Mixture 2:
    Buffered Iodide 40ml
    Thiosulfate Solution 10ml
    Distilled Water 20ml

    Mixture3:
    Buffered Iodide 40ml
    Thiosulfate Solution 10ml

    Mixture 4:
    Buffered Iodide 40ml
    Thiosulfate Solution 5 ml
    Distilled Water 5ml

    Separately put each beaker into ice water and measure the following amounts of peroxide solution separately into the container of ice:
    Mixture 1: 20ml
    Mixture 2: 10ml
    Mixture 3: 30ml
    Mixture 4: 30ml
    when the two flasks have cooled on ice below 3°C add the peroxide
    time as soon as you add peroxide into the flask

    I am unsure for my lab questions what values to use for each trial to calculate the moles of sodium thiosulfate reacted? and how to calculate the mol/L H2O2 reacted
     
  2. jcsd
  3. chemisttree

    chemisttree 3,723
    Science Advisor
    Homework Helper
    Gold Member

    Strangest lab I've ever seen.
     
  4. Borek

    Staff: Mentor

    How many moles of thiosulfate in 5 mL of 1M solution?

    What is the concentration of solution that contains this number of moles of thiosulfate in 200 mL?
     
  5. wouldn't the concentration be 1 M
     
  6. Borek

    Staff: Mentor

    No. Don't guess, try to calculate, following exactly questions as I listed them. This is mostly a simple plug and chug - use the definition of the concentration rearranged to isolate thing that you want to calculate.
     
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