chlorine gas bubbled into a potassium iodide solution in a test tube. explain why a dark brown colour is observed
From Google:
As more chlorine is added, the iodine reacts with the excess chlorine to form iodine trichloride and the solution decolorizes. ... When chlorine gas is bubbled into an aqueous solution of potassium iodide, some of the iodide ions are oxidized to iodine.
The observation of a dark brown color when chlorine gas is bubbled into a potassium iodide solution is due to a chemical reaction called the iodine clock reaction. This reaction involves the oxidation of iodide ions (I-) by chlorine gas (Cl2) to produce iodine (I2) and chloride ions (Cl-).
To understand the reaction, let's break it down step by step:
1. When chlorine gas is bubbled into the potassium iodide solution, the chlorine gas molecules dissociate into chlorine atoms (Cl). These chlorine atoms react with the iodide ions in water according to the equation:
Cl2 + 2I- → 2Cl- + I2
2. The iodine that is formed during this reaction is not very soluble in water, so it appears as fine particles or precipitates in the solution. These particles tend to aggregate and form larger clusters, giving the solution a dark brown color.
3. The dark brown color becomes more noticeable as more iodine is formed through the reaction between chlorine and iodide ions. This is because the concentration of iodine increases, resulting in a more intense color.
In summary, the dark brown color observed when chlorine gas is bubbled into a potassium iodide solution is a result of the formation of insoluble iodine particles that accumulate in the solution, imparting the characteristic color.