Rainbow Clock Reaction Equation Calculation??

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Rainbow Clock Reaction Equation Calculation??

Post by claiiiirrree »

I'm conducting the following experiment:

Solution A
• Dissolve 0.37 g of sodium thiosulfate in 200 mL of water in a beaker.
• Dissolve 9 g of potassium iodide in a separate 200 mL of water in a beaker.
• Combine these solutions in the volumetric flask.
• Add 4 mL of 0.1M ethanoic acid, then add water to adjust the total volume to 500 mL.
Solution B
• Measure 100 mL of solution A into a 250 mL beaker and mix in 3 drops of universal indicator.
• Freshly prepare 0.05M of hydrogen peroxide by diluting 7 mL of 6% hydrogen peroxide solution with 250 mL of water.

1. In a beaker, mix 100 mL of solution A with 30 mL of solution B.
2. Film the experiment and start the stopwatch from the time that solution A and B are combined, to the time at which the colour of the solution changes to a dark purple.
3. Repeat this process, changing the concentration to …. And conduct 3 trials of each.

In this experiment, the combination of solution A and solution B produces a solution which, once combined with universal pH indicator, will change through the colours of the rainbow, from red, orange, yellow, etc..... to purple.

Can anyone tell me what the equation of the reaction that is occurring between KI, CH3OOH, Na2S2O3 and H2O2 for the pH to change and thus create the colour change from the universal indicator?
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Post by ChenBeier »

Peroxide will oxidise the iodide to iodine purple color.
Thiosulfate will reduce back. pH change show the indicator.

KI + H+ => HI + K+ pH drop bei acetic acid

2 HI + H2O2 => 2 H2O + I2 Oxiding of Iodide.

I2 + 2 Na2S2O3 => 2 NaI +Na2S4O6 reduction of iodine.
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