Clock Reactions Flashcards
Iodine clock reactions
A method to find initial rate of reaction without drawing any graphs
Reaction 1
Hydrogen peroxide + iodine ions (from potassium iodide) + H+ ions (acidic conditions)
Makes water and iodine
Reaction 1: important product
Produces iodine
What does iodine produced from reaction 1 do?
React with thiosulfate ions (from sodium thiosulfate)
To start reaction 2
Reaction 2
Thiosulfate ions + iodine makes
Makes iodide ions and S4O8- ions
Iodide ions will…
Immediately react with hydrogen peroxide and hydrogen ions in reaction 1
So the iodide ions made from reaction 1 will immediately be recycled to reaction 2
When does the colour change occur?
When the sodium thiosulfate ions in reaction 2 run out
Reaction 2 cannot start
So the iodine can remain in solution instead of immediately reacting
Colour change
Iodine remaining in solution can react with starch to change colour to blue black
How can we assure reaction 1 will occur constantly so we can made iodine again from the iodide ions?
Have hydrogen peroxide be in excess
What are we measuring when we do this?
Time taken for colour change to occur
What are we measuring when we do this?
Time taken for colour change to occur
What is initial rate of reaction proportional to?
1/time taken for a colour change
