The color change occurs when I2 reacts with starch to form a dark blue iodine/starch complex. The ability to record the time at which the blue complex appears allows the rate of reaction to be determined accurately with a stopwatch. … You will also examine the effect of a metal ion catalyst on the reaction rate.
Why does the iodine clock reaction turn blue?
In an iodine clock reaction, the blue color is due to the starch–iodine complex, but the compound that is “trapped” by thio sulfate ions is iodine itself, which is reduced back to colorless iodide ions.
What does hydrogen peroxide do in iodine clock reaction?
In Reaction # 1 iodide ions react with hydrogen peroxide to produce iodine element which is blue in the presence of starch. BUT, before that can actually happen, the Vitamin C quickly reacts and consumes the elemental iodine.
What will happen to the color of the water and iodine solution Why?
In the first experiment, the iodine and water solution are a dark brown color until the starch is added. Then the solution changes to a dark bluish-black color. This happens because the iodine bonds with the starch to create a new compound. … So the solution stays clear.
What is the role of starch in the iodine clock reactions?
The starch solution serves as an indicator of the end of the reaction by forming a deep-blue colored starch–iodine complex. The reaction time can thus be measured by not- ing the time until the appearance of the blue color for each trial.
Why does starch and iodine turn blue?
Amylose in starch is responsible for the formation of a deep blue color in the presence of iodine. The iodine molecule slips inside of the amylose coil. … This makes a linear triiodide ion complex with is soluble that slips into the coil of the starch causing an intense blue-black color.
What occurs in an iodine clock reaction?
The iodine clock reaction exists in several variations, which each involve iodine species (iodide ion, free iodine, or iodate ion) and redox reagents in the presence of starch. … After a short time delay, the liquid suddenly turns to a shade of dark blue due to the formation of a triiodide–starch complex.
What are the two reactions that occur in the iodine clock reaction?
There are two reactions occurring in the solution. In the first, slow reaction, the triiodide ion is produced . H2O2(aq) + 3 I–(aq) + 2 H+ → I3– + 2 H2O. In the second, fast reaction, triiodide is reconverted to iodide by the thiosulfate.
What does vitamin C do in an iodine clock reaction?
The Vitamin C creates a clock reaction (1 – 2 minutes) and once it is used up, the solution turns blue, because now the iodine element and starch are present. Safety Precautions: Be careful when working with the iodine – it stains. Waste Disposal: Dispose all liquids down the drain with plenty of water.
How does temperature affect the iodine clock reaction?
After many trials to ensure accuracy, it was evident that temperature played a key role in reaction rates. The solutions made with cold water were the slowest to react, while the solutions made with hot water were the fastest to react.
What makes iodine Colourless?
A chemical reaction takes place in which the iodine gains an electron and changes from I2 element to iodide ions, I– . Due to this change, the iodine changes to an iodide ion which is colorless.
Why is iodine yellow in water?
The molecules can form a loosely bound Lewis-type charge transfer complex, in which there is a partial transfer of electrons from the water to the iodine. The formation of the complex changes the colour of light absorbed. A solution of iodine in water is yellow-brown instead of violet.
Why is iodine brown in water?
Why is iodine Brown in water? Iodine is non-polar and thus dissolves in methylene chloride by dispersion forces (induced dipole/induced dipole). A small amount of iodine may dissolve in the water initially due to dipole/induced-dipole interactions producing a slight brown color.