Answer :
Final answer:
A colour change occurs when a halogen and a sodium halide are mixed due to a displacement reaction. The more reactive halogen displaces the less reactive halogen from its sodium salt, which results in a colour change. The darkening of the solution color is due to the liberated iodine from sodium iodide when it reacts with chlorine.
Explanation:
The reaction you are asking about refers to the concept of displacement reactions in chemistry. Specifically, this is a type of halogen displacement reaction. When a solution of a halogen (like chlorine, bromine, or iodine) is mixed with a sodium halide (like sodium chloride, sodium bromide or sodium iodide), the halogen can displace a less reactive halogen from the sodium halide.
For instance, if you mix a solution of chlorine (a more reactive halogen) with a solution of sodium iodide (a sodium salt of less reactive halogen), a displacement reaction will occur. During this reaction, the chlorine will displace the iodine present in sodium iodide, leading to the formation of sodium chloride and iodine. The solution darkens in colour due to the liberation of iodine.
The reaction is: 2NaI + Cl2 ⟶ 2NaCl + I2
Learn more about Displacement Reactions here:
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