Chemical watches

Periodic solution changes color from colorless to yellow to black, etc.

Scientific name: The Briggs-Rauscher Iodine oscillating reaction - Periodic oxidation and reduction of iodine.

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Safety

Wear eye protection goggles and gloves.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

2KIO3 + 4H2O2 + 2CH2(COOH)2 + H2SO4 → 2ICH(COOH)2 + 4O2 + 6H2O + K2SO4

May be represented by the two following reactions:

2KIO3 + 4H2O2 + H2SO4 → 2HIO + 4O2 + 4H2O + K2SO4

HIO + CH2(CO2H)2 → ICH(COOH)2 + H2O

This reaction also consists of two component reactions:

2KI + 2HIO + H2SO4 → 2I2 + 2H2O + K2SO4

2I2CH2(CO2H)2 → 2ICH2(CO2H)2 + H2SO4 + 2KI

Step-by-step instruction

First, it is necessary to prepare three solutions, in large beakers:

  1. Add 210 ml of distilled water to 120 ml of 30% hydrogen peroxide solution. Measure volumes using measuring cylinders.
  2. Pour 14.3 g of potassium iodate into a beaker and add 200 ml of water. Due to the low solubility in water, potassium iodate solution must be heated on a hot plate. Then, add 1.5 ml of concentrated sulfuric acid. Further, it is necessary to increase the volume of the solution to equal to about 0.33 liters.
  3. Take a sample of manganese sulfate (3 g). Next, add 5.2 g of malonic acid. Then add 230 ml of distilled water. Then, it is necessary to add a small amount of pre-cooked starch paste solution and increase volume of the solution to equal to about 0.33 liters.

To perform the reaction.

  1. Immerse a magnetic stirrer in the third glass and set to shuffle.
  2. Next, add the second solution to the third solution, and finally the first.
  3. Thereafter the reaction begins.

Scientific background

The reaction has quite a complicated mechanism.

The yellow color is formed due to the appearance of free iodine.

The blue color is formed is due to the presence of the indicator for iodine in the solution.

The disappearance of the color due to the presence of the following process:

2KIO3 + 4H2O2 + 2CH2(COOH)2 + H2SO4 → 2ICH(COOH)2 + 4O2 + 6H2O + K2SO4

Oscillation damping occurs due to consumption of malonic acid.

Manganese ionshave a catalycal value.

Danger:
Coolness:
Difficulty:

Published on 10 March 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst